485BPOS

As filed with the Securities and Exchange Commission on April 30, 2007

Securities Act registration no. 2-34223

Investment Company Act file no. 811-1829

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C.  20549

FORM N-1A

REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933

Post-Effective Amendment No. 80

and

REGISTRATION STATEMENT UNDER THE INVESTMENT COMPANY ACT OF 1940

Amendment No. 55

COLUMBIA ACORN TRUST

227 West Monroe Street, Suite 3000
Chicago, Illinois  60606

Telephone number:  312/634-9200

Charles P. McQuaid	Michelle Rhee	Cameron S. Avery
Columbia Acorn Trust	Columbia Management Group, LLC	Bell, Boyd & Lloyd LLP
227 West Monroe Street, Suite 3000	One Financial Center	70 West Madison Street, Suite 3100
Chicago, Illinois  60606	Boston, Massachusetts  02111	Chicago, Illinois  60602

(Agents for service)

Amending Parts A, B, and C, and filing exhibits

It is proposed that this filing will become effective:

o    immediately upon filing pursuant to rule 485(b)

x    on May 1, 2007 pursuant to rule 485(b)

o    60 days after filing pursuant to rule 485(a)(1)

o    on                     pursuant to rule 485(a)(1)

o    75 days after filing pursuant to rule 485(a)(2)

o    on                     pursuant to rule 485(a)(2).

Columbia^SM

Acorn^® Fund  Prospectus, May 1, 2007

Class A, B and C Shares

Advised by Columbia Wanger Asset Management, L.P.

TABLE OF CONTENTS

THE FUND	2
Investment Goal	2
Principal Investment Strategies	2
Principal Investment Risks	2
Portfolio Holdings Disclosure	3
Performance History	4
Commissions and Other Expenses	6
YOUR ACCOUNT	8
Choosing a Share Class	8
How to Buy Shares	9
Investment Minimums	9
Sales Charges (Commissions)	10
How to Exchange Shares	15
How to Sell Shares	16
Fund Policy on Trading of Fund Shares	17
Other Information About Your Account	19
BOARD OF TRUSTEES	21
MANAGING THE FUND	22
Investment Adviser	22
Portfolio Managers	22
Legal Proceedings	23
OTHER INVESTMENT STRATEGIES AND RISKS	24
The Information Edge	24
Long-Term Investing	25
Derivative Strategies	25
Temporary Defensive Strategies	26
FINANCIAL HIGHLIGHTS	27
APPENDIX	30

Although these securities have been registered with the Securities and Exchange Commission, the Commission has not approved or disapproved any shares offered in this prospectus or determined whether this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Acorn^® is a trademark owned and registered by Columbia Acorn Trust, Columbia, Columbia Management^® and Columbia Management Services, Inc. are service marks owned and/or registered by Bank of America

The Fund

INVESTMENT GOAL

Columbia Acorn Fund (Acorn^® Fund) seeks to provide long-term growth of capital.

PRINCIPAL INVESTMENT STRATEGIES

Acorn Fund invests generally in the stocks of small- and medium-sized companies. The Fund generally invests in the stocks of companies with market capitalizations of less than $5 billion at the time of initial purchase. As long as a stock continues to meet the Fund's other investment criteria, the Fund may choose to hold the stock even if the issuing company's capitalization grows beyond a $5 billion capitalization.

Acorn Fund believes that these smaller companies, which are not as well known by financial analysts, may offer higher return potential than the stocks of larger companies.

Acorn Fund typically looks for companies with:

•  A strong business franchise that offers growth potential.

•  Products and services that give a company a competitive advantage.

•  A stock price the Fund's investment adviser believes is reasonable relative to the assets and earning power of the company.

Acorn Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its assets in companies outside the United States in developed markets (for example, Japan, Canada and the United Kingdom) and emerging markets (for example, Mexico, Brazil and Korea).

Additional strategies that are not principal investment strategies and the risks associated with them are described later in this prospectus under "Other Investment Strategies and Risks."

PRINCIPAL INVESTMENT RISKS

The principal risks of investing in the Fund are described below. There are many circumstances (including additional risks that are not described here) which could prevent the Fund from achieving its investment goal. You may lose money by investing in the Fund.

Management risk means that the adviser's investment decisions might produce losses or cause the Fund to underperform when compared to other funds with a similar investment goal. Market risk means that security prices in a market, sector or industry may fall, reducing the value of your investment. Because of management and market risk, there is no guarantee that the Fund will achieve its investment goal or perform favorably among comparable funds.

Since the Fund purchases equity securities, it is subject to equity risk. This is the risk that stock prices will fall over short or extended periods of time. Although the stock market historically has outperformed other asset classes over the long term, the stock market tends to move in cycles. Individual stock prices may fluctuate drastically from day-to-day and may underperform other asset classes over an extended period of time. Individual companies may report poor results or be negatively affected by industry and/or economic trends and developments. The prices of securities issued by such companies may suffer a decline in response. These price movements may result from factors affecting individual companies, industries or the securities market as a whole.

Because the Fund invests in stocks, the price of its shares — its net asset value (NAV) per share — fluctuates daily in response to changes in the market value of stocks.

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The Fund

Sector risk is inherent in the Fund's investment strategy. Companies that are in different but closely related industries are sometimes described as being in the same broad economic sector. The values of stocks of different companies in a market sector may be similarly affected by particular economic or market events. Although the Fund does not intend to focus on any particular sector, at times the Fund may have a large portion of its assets invested in a particular sector.

Foreign securities are subject to special risks. Foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the dollar value of foreign securities denominated in foreign currencies and U.S. dollars, without a change in the intrinsic value of those securities. The liquidity of foreign securities may be more limited than that of domestic securities, which means that the Fund may, at times, be unable to sell foreign securities at desirable prices. Brokerage commissions, custodial fees and other fees are generally higher for foreign investments. In addition, foreign governments may impose withholding taxes that would reduce the amount of income and capital gains available to distribute to shareholders. Other risks include possible delays in the settlement of transactions or in the notification of income; less publicly av ailable information about companies; the impact of political, social or diplomatic events; possible seizure, expropriation or nationalization of the company or its assets; and possible imposition of currency exchange controls.

Investments in emerging markets are subject to additional risk. The risks of foreign investments are typically increased in less developed countries, which are sometimes referred to as emerging markets. For example, political and economic structures in these countries may be new and developing rapidly, which may cause instability. These countries are also more likely to experience high levels of inflation, deflation or currency devaluations, which could hurt their economies and securities markets.

Small- or mid-cap companies may be more susceptible to market downturns, and their prices could be more volatile than large-cap companies. These companies are more likely than larger companies to have limited product lines, operating histories, markets or financial resources. They may depend heavily on a small management team and may trade less frequently, may trade in smaller volumes and may fluctuate more sharply in price than stocks of larger companies. In addition, such companies may not be widely followed by the investment community, which can lower the demand for their stocks.

An investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PORTFOLIO HOLDINGS DISCLOSURE

A description of the Fund's policies and procedures with respect to the disclosure of its portfolio securities is available in the Fund's Statement of Additional Information (SAI), which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611.

The Fund posts its complete portfolio holdings as of month-end at www.columbiafunds.com approximately 30-40 calendar days after such month-end. Additionally, the Fund discloses its top 15 month-end portfolio holdings at www.columbiafunds.com on or about 15 calendar days following such month-end.

Once posted, the above information will remain available on the website until at least the date on which the Fund files a Form N-CSR or Form N-Q for the period that includes the date as of which the information is current.

3

The Fund

PERFORMANCE HISTORY

The bar chart below shows the Fund's calendar-year total returns (before taxes) for its Class A shares, excluding sales charges. The performance table following the bar chart shows how the Fund's average annual total returns for Class A, B and C shares, including sales charges, compare with broad measures of market performance for one year, five years and the life of the share class. The chart and table are intended to illustrate some of the risks of investing in the Fund by showing changes in the Fund's performance from year to year. All returns include the reinvestment of dividends and distributions. As with all mutual funds, past performance (before and after taxes) does not predict the Fund's future performance.

UNDERSTANDING PERFORMANCE

Calendar Year Total Returns show the Fund's Class A share performance for each completed calendar year since the Class commenced operations. Those returns include the effects of Fund expenses, but not the effects of sales charges paid directly by a shareholder. If sales charges were included, these returns would be lower.

Average Annual Total Returns are a measure of the Fund's average performance over the past one year, five years and the life of the share class. The table shows returns of each share class and includes the effects of both Fund expenses and current sales charges. Class B share returns do not reflect Class A share returns after conversion of Class B shares to Class A shares — see the section "Your Account — Sales Charges (Commissions)."

The Fund's returns are compared to the Russell 2500 Index (Russell 2500), Standard & Poor's 500 Index (S&P 500 Index) and the Russell 2000^® Index (Russell 2000^®). The Russell 2500, the Fund's primary benchmark, is a market-weighted index of the 2500 smallest companies that is formed by taking the 3000 largest U.S. companies and eliminating the largest 500 of those companies. The S&P 500 Index is a broad market-weighted average of 500 widely-held large capitalization U.S. stocks. The Russell 2000^® is a market-weighted index of the 2000 smallest companies of the 3000 largest U.S. companies based on market capitalization. All third-party trademarks are the property of their owners. Unlike the Fund, indices are not investments, do not incur fees, expenses or taxes, and are not professionally managed.

Calendar Year Total Returns (Class A)

For the periods shown in bar chart:
Best quarter: 2nd quarter 2003, +19.85%
Worst quarter: 3rd quarter 2001, -18.69%

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The Fund

After-tax returns are calculated using the highest historical individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on each investor's own tax situation and may differ from those shown. After-tax returns may not be relevant to investors who hold Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Average Annual Total Returns — for periods ended December 31, 2006⁽¹⁾

Share Class	1 Year		5 Years		Life of the Share Class(2)
Class A (%)
Return Before Taxes		7.57		12.88		12.49
Return After Taxes on Distributions		6.22		12.27		11.51
Return After Taxes on Distributions and Sale of Fund Shares		6.50		11.22		10.65
Class B (%)
Return Before Taxes		8.43		13.22		12.82
Return After Taxes on Distributions		7.00		12.60		11.83
Return After Taxes on Distributions and Sale of Fund Shares		7.22		11.53		10.97
Class C (%)
Return Before Taxes		12.25		13.41		12.77
Return After Taxes on Distributions		10.82		12.80		11.79
Return After Taxes on Distributions and Sale of Fund Shares		9.71		11.70		10.92
Indices
Russell 2500 (%)		16.17		12.19		10.48	(3)
S&P 500 Index (%)		15.79		6.19		2.22	(3)
Russell 2000® (%)		18.37		11.39		9.67	(3)

(1)  Performance may reflect any voluntary waiver or reimbursement of Fund expenses by the investment adviser or its affiliates. Absent these waivers or reimbursement arrangements, performance results would have been lower.

(2)  The inception date for Class A, Class B and Class C shares is October 16, 2000.

(3)  Performance information is from October 16, 2000.

5

The Fund

COMMISSIONS AND OTHER EXPENSES

Expenses are one of several factors to consider before you invest in a mutual fund. The tables below describe the commissions and other expenses you may pay when you buy, hold and sell shares of the Fund.

UNDERSTANDING EXPENSES

Sales Charges (Commissions) are paid directly by shareholders to Columbia Management Distributors, Inc., the Fund's distributor, who compensates your financial advisor.

Annual Fund Operating Expenses are paid by the Fund. They include management and administration fees, 12b-1 fees and other expenses that generally include, but are not limited to, transfer agency, custody, and legal fees as well as costs related to state registration and printing of Fund documents. The specific fees and expenses that make up the Fund's other expenses will vary from time to time and may include fees or expenses not described here. The Fund will likely incur portfolio transaction costs that are in addition to the total annual fund operating expenses disclosed in the fee table. These transaction costs are made up of all costs that are associated with trading securities for the Fund's portfolio and include, but are not limited to, brokerage commissions and market spreads, as well as potential changes to the price of a security due to the Fund's efforts to purchase or sell it. While certain elements of transaction costs are readily identifiable and quantifiable, other elements that can make up a significant amount of the Fund's transaction costs are not. Higher transaction costs reduce the Fund's returns.

Shareholder Fees (commissions paid directly from your investment)

	Class A			Class B		Class C
Maximum sales charge (load) on purchases (%) (as a percentage of the offering price)		5.75		None		None
Maximum deferred sales charge (load) on redemptions (%) (as a percentage of the lesser of purchase price or redemption price)		1.00	(1)		5.00		1.00
Redemption fee (%) (as a percentage of amount redeemed, if applicable)	None(2)			None(2)		None(2)

(1)  This charge applies only to certain purchases of Class A shares bought without an initial sales charge that are sold within 12 months of purchase.

(2)  There is a $7.50 charge for wiring sale proceeds to your bank.

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The Fund

Annual Fund Operating Expenses (deducted directly from Fund assets)

	Class A		Class B		Class C
Management fees(1) (%)		0.64		0.64		0.64
Distribution and service (12b-1) fees(2) (%)		0.25		0.75		1.00
Other expenses(3) (%)		0.16		0.24		0.20
Total annual fund operating expenses (%)		1.05		1.63		1.84

(1)  The Fund pays an investment advisory fee of 0.64%. The Fund and its adviser have implemented a breakpoint schedule for the Fund's investment advisory fees. The investment advisory fee rates charged to the Fund will decline as Fund assets grow and will continue to be based on a percentage of the Fund's average daily assets. The annual fee schedule for the Fund is as follows: 0.74% for assets up to $700 million; 0.69% for assets in excess of $700 million and up to $2 billion; 0.64% for assets in excess of $2 billion and up to $6 billion; and 0.63% for assets in excess of $6 billion. In addition to the management fee, the Fund and the other funds of Columbia Acorn Trust (the "Trust") pay the adviser an administrative fee based on the average daily aggregate net assets of the Trust at the following annual rates: 0.05% of net assets up to $8 billion; 0.04% of the next $8billion; and 0.03% of net assets in excess of $16 billion. Based on the Trust's average daily net assets as of December 31, 2006, the administrative fee would be at a rate of 0.04% and is included in "Other expenses."

(2)  The distribution and service (12b-1) fees for Class B shares have been restated to reflect a reduction of the distribution fee rate by 0.10%, effective August 1, 2006.

(3)  "Other expenses" have been restated to reflect contractual changes to the transfer agency fees paid by the Fund.

Example Expenses help you compare the cost of investing in the Fund to the cost of investing in other mutual funds. It uses the following hypothetical conditions:

•  $10,000 initial investment^†

•  5% total return for each year

•  Fund operating expenses remain the same

•  Reinvestment of all dividends and distributions

•  Class B shares convert to Class A shares after eight years

†  For example only, since the minimum initial investment in the Fund is $75,000.

Example Expenses for a $10,000 investment (your actual costs may be higher or lower)

Class		1 Year		3 Years		5 Years		10 Years
Class A:		$	676	$	890	$	1,121	$	1,784
Class B:	did not sell your shares	$	166	$	514	$	887	$	1,778
	sold all your shares at the end of the period		$666		$814		$1,087		$1,778
Class C:	did not sell your shares	$	187	$	579	$	995	$	2,159
	sold all your shares at the end of the period		$287		$579		$995		$2,159

See the Appendix for additional hypothetical investment and expense information.

7

Your Account

CHOOSING A SHARE CLASS

The Fund offers three classes of shares in this prospectus – Class A, Class B and Class C. Each share class has its own commission and expense structure that affects the investment return of that class. Determining which share class is best for you depends on various factors, including the amount you are investing, how long you expect to hold your investment and your personal situation.

You should consult with your financial advisor before deciding which share class is most appropriate for you. The following considerations should be part of your assessment:

•  You will pay a commission if you buy Class A, B or C shares, either at the time of investment or redemption, or through ongoing distribution commission payments (Rule 12b-1 fees) made from your investment over time, or both.

•  Class A shares require an up-front commission payment, but pay lower ongoing Rule 12b-1 fees than Class B and Class C shares. Class B and Class C shares have no up-front commission paid by the shareholder but pay higher ongoing commissions (Rule 12b-1 fees), a deferred commission is imposed on a redemption of Class B shares within six years after purchase and a deferred commission is imposed on a redemption of Class C shares within one year of purchase. The differential between classes will vary depending on the actual investment return for any given period.

•  Class A shares can be more advantageous to an investor who intends to hold the shares for several years and invests an amount large enough to qualify for a reduced rate of initial sales commission, taking into account the commissions that investor may pay when redeeming shares of other classes. To project whether Class A shares might be more advantageous to you, you should consider, among other factors, the time period you intend to hold the shares, your initial sales commission and a comparison of the total annual expenses of Class A shares to the expenses of other share classes. Class A shares pay an ongoing annual commission (Rule 12b-1 fee) of up to 0.25% of the average value of the shares.

•  Class B shares are no longer offered to new investors. A Class B shareholder of the Fund whose account has a value of less than $50,000 (including for this purpose the combined value of all eligible accounts maintained by that shareholder that would be used to determine eligibility for reduced sales charges on Class A shares) may purchase additional Class B shares of the Fund to increase the account value up to a maximum of $49,999; any additional investment by the shareholder in that Fund will be invested in Class A shares of the Fund, without regard to the normal investment minimum for Class A shares, but will be subject to the applicable Class A shares up-front commission. Class B shares pay an ongoing annual commission (Rule 12b-1 fee) of up to 0.75% of the average value of the shares and automatically convert to Class A shares after eight years.

•  Class C shares are generally more advantageous to an investor who intends to hold shares for only a few years. Class C shares pay an ongoing annual commission (Rule 12b-1 fee) of up to 1.00% of the average value of the shares.

•  If you invest $1 million or more, you can purchase Class A shares but not Class C shares.

The Fund also offers an additional class of shares, Class Z shares, exclusively to certain institutional and other eligible investors. Class Z shares are made available through a separate prospectus provided to eligible institutional and other investors.

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Your Account

HOW TO BUY SHARES

Your financial advisor can help you establish an appropriate investment portfolio, buy shares and monitor your investments. When the Fund receives your purchase request in "good form," your shares will be bought at the next calculated public offering price. "Good form" means that the Fund's transfer agent has all information and documentation it deems necessary to effect your order. For example "good form" may mean that you have properly placed your order with your financial advisor or the Fund's transfer agent has received your completed application, including all necessary signatures. The Fund reserves the right to refuse a purchase order for any reason, including if the Fund believes that doing so would be in the best interest of the Fund and its shareholders. The USA PATRIOT Act may require us to obtain certain personal information from you that we will use to verify your identity. If you do not provide the information, we m ay not be able to open your account. If we are unable to verify your customer information, we reserve the right to close your account or take such other steps as we deem reasonable.

INVESTMENT MINIMUMS

The investment minimum for initial investments (by purchase, exchange or certain transfers) of Class A, B and C shares is $75,000. The investment minimum is applied at the class level. For group retirement plans, the investment minimum is determined based on the amount of the plan's investment rather than that of its individual participants. The Fund may establish exclusions from the investment minimum from time to time that it deems appropriate and consistent with the interests of shareholders. Please see the SAI for details on these exclusions. The Fund reserves the right to change these investment minimums.

The Fund also reserves the right to refuse a purchase order for any reason, including if it believes that doing so would be in the best interest of the Fund and its shareholders. Finally, pursuant to the Trust's Agreement and Declaration of Trust, the Fund reserves the right to redeem your shares if your account falls below the minimum investment requirements.

Please see the SAI for more details on investment minimums.

Outlined below are the various options for buying shares:

Method	Instructions
Through your financial advisor	Your financial advisor can help you establish your account and buy Fund shares on your behalf. To receive the current trading day's price, your financial advisor must receive your request prior to the close of regular trading on the New York Stock Exchange (NYSE), usually 4:00 p.m. Eastern time. Your financial advisor may charge you fees for executing the purchase for you.
By check (new account)	For new accounts, send a completed application and check made payable to the Fund to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By check (existing account)	For existing accounts, fill out and return the additional investment stub included in your account statement, or send a letter of instruction including your name, the Fund's share class and account number with a check made payable to the Fund to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By exchange	You or your financial advisor may acquire Fund shares for your account by exchanging shares you own in a different fund distributed by Columbia Management Distributors, Inc. for shares of the same class (and, in some cases, certain other classes) of the Fund at no additional cost. An exchange to another fund may incur a sales charge if the original purchase was not assessed a sales charge. To exchange by telephone, call 1-800-422-3737. Please see "How to Exchange Shares" for more information.
By wire	You may purchase Fund shares by wiring money from your bank account to your Fund account. To wire funds to your Fund account, call 1-800-422-3737 for wiring instructions.

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Your Account

Method	Instructions
By electronic funds transfer	You may purchase Fund shares by electronically transferring money from your bank account to your Fund account by calling 1-800-422-3737. An electronic funds transfer may take up to two business days to settle and must be considered in "good form." You must set up this feature prior to your telephone request. Be sure to complete the appropriate section of the application for this feature.
Automatic investment plan	You may make monthly or quarterly investments ($50 minimum) automatically from your bank account to your Fund account. You may select a pre-authorized amount to be sent via electronic funds transfer. Be sure to complete the appropriate section of the application for this feature.
Automated dollar cost averaging	You may purchase Fund shares for your account by exchanging $100 or more each month from another fund for shares of the same class of the Fund at no additional cost. Exchanges will continue so long as your fund balance is sufficient to complete the transfers. You may terminate your program or change the amount of the exchange (subject to the $100 minimum) by calling 1-800-345-6611. There may be an additional sales charge if exchanging from a money market fund. Be sure to complete the appropriate section of the account application for this feature.
By dividend diversification	You may automatically invest dividends distributed by another fund into the same class of shares (and, in some cases, certain other classes) of the Fund at no additional sales charge. There may be an additional sales charge if automatically investing dividends from a money market fund. To invest your dividends in the Fund, call 1-800-345-6611.
Through the internet	You may purchase Fund shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet purchases. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

SALES CHARGES (COMMISSIONS)

You may be subject to an initial sales charge when you purchase, or a contingent deferred sales charge (CDSC) when you sell, shares of the Fund. These sales charges are described below. In certain circumstances, the sales charge may be reduced or waived, as described below and in the SAI.

Rule 12b-1 Plan The Fund has adopted a plan under Rule 12b-1 under the Investment Company Act that permits it to pay its distributor ongoing sales and marketing fees (commissions) to support the sale and distribution of Class A, B and C shares and certain services provided to you by your financial advisor, and your financial advisor may receive all or a portion of those fees attributable to your shares. The annual fee, as a percentage of the value of the shares, is normally 0.25% for Class A, 0.75% for Class B and 1.00% for Class C shares. These fees are paid out of the assets of these share classes. Over time, these fees reduce the return on your investment. Class B shares automatically convert to Class A shares after eight years, eliminating a portion of the Rule 12b-1 fee thereafter.

Financial Intermediary Payments

The Fund's distributor, investment adviser or their affiliates may make payments, from their own resources, to certain financial intermediaries, including other Bank of America affiliates, for marketing support services. For purposes of this section the term "financial intermediary" includes any broker, dealer, bank, bank trust department, registered investment adviser, financial planner, retirement plan or other third-party administrator and any other institution having a selling, services or any similar agreement with the Fund's distributor, investment adviser or one of their affiliates. These payments are generally based upon one or more of the following factors: average net assets of the mutual funds distributed by the Fund's distributor attributable to that financial intermediary, gross sales of the mutual funds distributed by the Fund's distributor attributable to that financial intermediary, reimbursement of ticket charge s (fees that a financial intermediary firm charges its representatives for effecting transactions in fund shares) or a negotiated lump sum payment.

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Your Account

While the financial arrangements may vary for each financial intermediary, the payments to any one financial intermediary are generally expected to be between 0.05% and 0.35% on an annual basis for payments based on average net assets of the Fund attributable to the financial intermediary, and between 0.10% and 0.25% on an annual basis for firms receiving a payment based on gross sales of the Fund attributable to the financial intermediary. The Fund's distributor, investment adviser or their affiliates may make payments in materially larger amounts or on a basis materially different from those described above when dealing with other affiliates of Bank of America. Such increased payments to the other Bank of America affiliate may enable the other Bank of America affiliate to offset credits that it may provide to its customers in order to avoid having such customers pay fees to multiple Bank of America entities in connection with the customer's investment in the Fund.

Payments also may be made to certain financial intermediaries, including other Bank of America affiliates, that provide investor services to retirement plans and other investment programs to compensate financial intermediaries for services they provide to such programs, including, but not limited to, sub-accounting, sub-transfer agency, similar shareholder or participant recordkeeping, shareholder or participant reporting, or shareholder or participant transaction processing. These payments for investor servicing support vary by financial intermediary but generally are not expected, with certain limited exceptions, to exceed 0.35% of the total Fund assets for Class A, B and C shares in the program on an annual basis.

The Trust's Board of Trustees has authorized the Fund to pay to any intermediary up to 0.05% of the average aggregate value of Fund shares in the intermediary's program on an annual basis for providing investor services. Charges of an intermediary in excess of that paid by the Fund will be borne by the Fund's distributor or its affiliates.

The Fund's distributor, investment adviser or their affiliates may make other payments or allow promotional incentives to financial intermediaries to the extent permitted by the rules of the Securities and Exchange Commission, the National Association of Securities Dealers and by other applicable laws and regulations.

Amounts paid by the Fund's distributor, investment adviser or their affiliates are paid out of the distributor's, investment adviser's or their affiliates' own resources and do not increase the amount paid by you or the Fund. You can find further details about the payments made by the Fund's distributor, investment adviser or their affiliates and the services provided by financial intermediaries as well as a list of the financial intermediaries to which the Fund's distributor, investment adviser or their affiliates have agreed to make marketing support payments in the Fund's SAI, which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611. Your financial intermediary may charge you fees or commissions in addition to those disclosed in this prospectus. You can ask y our financial intermediary for information about any payments it receives from the Fund's distributor, investment adviser and their affiliates and any services your financial intermediary provides, as well as fees and/or commissions it charges. In addition, depending on the financial arrangement in place at any particular time, a financial intermediary and its financial consultants also may have a financial incentive for recommending a particular fund or share class over others. You should consult with your financial adviser and review carefully any disclosure by the financial intermediary as to compensation received by your financial adviser.

Class A shares Your purchases of Class A shares are made at the public offering price for these shares. This price includes a sales charge that is based on the amount of your initial investment when you open your account. The sales charge you pay on an additional investment is based on the total amount of your purchase and the current value of your account. Shares you purchase with reinvested dividends or other distributions are not subject to a

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Your Account

sales charge. A portion of the sales charge is paid as a commission to your financial advisor on your purchase of Class A shares. The amount of the sales charge differs depending on the amount you invest as shown in the table below.

Class A Sales Charges

	Sales Charge as % of:				% of offering price
Amount of purchase*	offering price		net amount invested		retained by your financial advisor
Less than $50,000**		5.75		6.10		5.00
$50,000 to less than $100,000**		4.50		4.71		3.75
$100,000 to less than $250,000		3.50		3.63		2.75
$250,000 to less than $500,000		2.50		2.56		2.00
$500,000 or more		2.00		2.04		1.75

*  Mutual fund wrap programs and group retirement plans that invest $75,000 or more in Class A shares of the Fund will not be subject to a sales charge.

**  Initial purchases of less than $75,000 are no longer accepted. However, for accounts opened prior to February 3, 2006, subsequent investments that do not meet the Fund's current investment minimum will be accepted.

In addition to the initial sales charge paid to your financial advisor and distributor, a 0.25% annual commission is paid to your financial advisor over the life of your investment out of your Fund assets as a 12b-1 fee.

The Fund's distributor may also pay additional compensation to financial advisors as an incentive for promoting the sale of shares of funds that it distributes.

Class A shares bought without an initial sales charge in accounts aggregating $1 million to $50 million at the time of purchase are subject to a 1.00% CDSC if the shares are sold within 12 months of the time of purchase. Subsequent Class A share purchases that bring your account value above $1 million (but less than $50 million) are subject to a CDSC if redeemed within 12 months of the date of purchase. The 12-month period begins on the first day of the month in which the purchase was made. The CDSC does not apply to retirement plans purchasing shares through a fee-based program.

For Class A share purchases of $1 million or more, financial advisors receive a cumulative commission from the distributor as follows:

Purchases Over $1 Million

Amount purchased	Commission %
$1 million to less than $3 million		1.00
$3 million to less than $50 million		0.50
$50 million or more		0.25

For group retirement plans, financial advisors are eligible to receive a 1.00% commission from the distributor on purchases, including those in amounts less than $1 million, that are coded as commission eligible trades. In determining the commission payable to a financial advisor in the above table, the breakpoint discount policies described in "Reduced Sales Charges (Commissions) for Larger Investments," on page 13, shall apply.

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UNDERSTANDING CONTINGENT DEFERRED SALES CHARGES (COMMISSIONS)

Certain investments in Class A, B and C shares are subject to a CDSC, a sales charge applied at the time you sell your shares. You will pay the CDSC only on shares you sell within a certain amount of time after purchase. The CDSC generally declines each year until there is no charge for selling shares. The CDSC is applied to the net asset value at the time of purchase or sale, whichever is lower. For purposes of calculating the CDSC, the start of the holding period is the first day of the month in which the purchase was made. Shares you purchase with reinvested dividends or other
distributions are not subject to a CDSC. When you place an order to sell shares, the Fund will automatically sell first those shares not subject to a CDSC and then those you have held the longest.

Reduced Sales Charges (Commissions) for Larger Investments.

A.  What are the principal ways to obtain a breakpoint discount?

There are two principal ways you may pay a lower sales charge (often referred to as "breakpoint discounts") when purchasing Class A shares of the Fund and other funds in the Columbia family of funds.

Rights of Accumulation The value of eligible accounts maintained by you and each member of your immediate family may be combined with the value of your current purchase to reach a sales charge discount level (according to the chart on the previous page) and to obtain the lower sales charge for your current purchase. To calculate the combined value of the accounts, the Fund will use the shares' current public offering price.

Statement of Intent You also may pay a lower sales charge when purchasing Class A shares by signing a Statement of Intent. By doing so, you would be able to pay the lower sales charge on all purchases made under the Statement of Intent within 13 months. As described in the chart on the previous page, the first breakpoint discount will be applied when total purchases reach $50,000. If your Statement of Intent purchases are not completed within 13 months, you will be charged the applicable sales charge on the amount you had invested to that date. To calculate the total value of your Statement of Intent purchases, the Fund will use the historic cost (i.e. dollars invested) of the shares held in each eligible account. You must retain all records necessary to substantiate historic costs because the Fund and your financial intermediary may not maintain this information.

B.  What accounts are eligible for breakpoint discounts?

The types of eligible accounts that may be aggregated to obtain one or both of the breakpoint discounts described above include:

•  Individual accounts

•  Joint accounts

•  Certain IRA accounts

•  Certain trusts

•  UTMA/UGMA accounts

For the purposes of obtaining a breakpoint discount, members of your "immediate family" include your spouse, parent, stepparent, legal guardian, child, stepchild, father-in-law and mother-in-law. Eligible accounts include those registered in the name of your dealer or other financial intermediary through which you own Columbia

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fund shares. An account is not eligible to the extent it holds an institutional class of shares of a Columbia money market fund or Class R shares of any Columbia fund. The value of your investment in a non-institutional class of a Columbia money market fund held in an eligible account may be aggregated with your investments in other funds in the Columbia family of funds to obtain a breakpoint discount through a Right of Accumulation. Non-institutional class investments in Columbia money market funds may also be included in the aggregation for a Statement of Intent for shares that have been charged a commission.

C.  How do I obtain a breakpoint discount?

The steps necessary to obtain a breakpoint discount depend on how your account is maintained with the Columbia family of funds. To obtain any of the above breakpoint discounts, you must notify your financial advisor at the time you purchase shares of the existence of each eligible account maintained by you or your immediate family. It is the sole responsibility of your financial advisor to ensure that you receive discounts for which you are eligible, and the Fund is not responsible for a financial advisor's failure to apply the eligible discount to your account. You may be asked by the Fund or your financial advisor for account statements or other records to verify your discount eligibility, including, where applicable, records for accounts opened with a different financial advisor and records of accounts established by members of your immediate family. If you own shares exclusively through an account maintained with the Fund's transfer agent, Columbia Management Services, Inc., you will need to provide the foregoing information to a Columbia Management Services, Inc. representative at the time you purchase shares.

D.  How can I obtain more information about breakpoint discounts?

Certain investors, including affiliates of the Fund, broker/dealers and their affiliates, investors in wrap-fee programs through fee-based advisers or certain retirement plans, certain shareholders of funds that were reorganized into other Columbia funds, and investors using the proceeds of redemptions of Fund shares or of certain Bank of America trust or similar accounts may purchase shares at a reduced sales charge or net asset value, which is the value of a fund share excluding any sales charges. CDSCs may also be waived for redemptions under a systematic withdrawal program, in connection with the death or post-purchase disability of a shareholder, certain medical expenses, charitable gifts, involuntary and tax-related redemptions, or when the selling broker/dealer has agreed to waive or return its commission. Restrictions may apply to certain accounts and certain transactions. Further information regarding these discounts ma y be found in the Fund's SAI, which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611.

Class B shares No new Class B share accounts may be established in the Fund. However, Class B share accounts established prior to February 3, 2006 may nonetheless purchase additional Class B shares at Class B's net asset value, so long as those purchases do not result in the account holding $50,000 or more of Class B shares (including for this purpose the combined value of all eligible accounts maintained by you that would be used to determine eligibility for reduced sales charges on Class A shares). In the event that an existing Class B shareholder seeks to add funds to such an account so that the balance would be in excess of $49,999, the amount in excess may be invested in Class A shares without the imposition of the minimum investment requirement for Class A shares. Such purchases of Class A shares will be subject to the applicable sales load impo sed on such purchases. See "Class A Sales Charges" on page 12.

Class B shares have no front-end sales charge, but they do carry a CDSC that is imposed only on shares sold within six years of purchase. The CDSC declines over the six years and disappears in the seventh year. The

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distributor pays your financial advisor an up-front commission on sales of Class B shares as described in the chart below. In addition, Class B shares bear ongoing service and distribution fees that are higher than those borne by Class A shares.

Purchases of less than $50,000⁽¹⁾:

Class B Sales Charges

Holding period after purchase	% deducted when shares are sold(2)
Through first year		5.00
Through second year		4.00
Through third year		3.00
Through fourth year		3.00
Through fifth year		2.00
Through sixth year		1.00
Longer than six years		0.00

(1)  Only applicable to accounts opened prior to February 3, 2006.

(2)  Applied to the net asset value at the time of purchase or sale, whichever is lower.

In addition, from the annual fee of 0.75% of the value of your shares paid out of your Fund assets as Rule 12b-1 fees, the distributor receives 0.50% of the value of the shares for each of the first eight years, or an aggregate 4.00% over eight years, which will offset the commission it paid to your financial advisor. Your financial advisor is paid the remaining 0.25% as an ongoing commission for the life of your investment.

The conversion of Class B shares to Class A shares occurs automatically eight years after purchase.

Class C shares Your purchases of Class C shares are at Class C's net asset value. Although Class C shares have no front-end sales charge, they carry a CDSC of 1.00% that is applied to shares sold within the first year after they are purchased. After holding shares for one year, you may sell them at any time without paying a CDSC. The distributor pays your financial advisor an up-front commission of 1.00% on your purchase of Class C shares, for which the distributor is repaid from the ongoing annual fee of 1.00% of the value of your shares paid out of your Fund assets as Rule 12b-1 fees, which is higher than the Rule 12b-1 fees borne by Class A and Class B shares.

Class C Sales Charges

Holding period after purchase	% deducted when shares are sold(1)
Through one year		1.00
Longer than one year		0.00

(1)  Applied to the net asset value at the time of purchase or sale, whichever is lower.

A 1.00% annual commission is paid to your financial advisor and the distributor over the life of your investment out of your Fund assets.

HOW TO EXCHANGE SHARES

You may exchange your shares for shares of the same share class (and in some cases, certain other classes) of another fund distributed by Columbia Management Distributors, Inc. at net asset value. If your shares are subject

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to a CDSC, you will not be charged a CDSC upon the exchange. However, when you sell the shares acquired through the exchange, the shares sold may be subject to a CDSC, depending upon when you originally purchased the shares you are exchanging. For purposes of computing the CDSC, the length of time you have owned your shares will be computed from the date of your original purchase and the applicable CDSC will be the CDSC of the original fund. Shareholders of Columbia Acorn Funds that qualify to purchase Class A shares at net asset value may exchange their Class A shares for Class Z shares of another fund distributed by Columbia Management Distributors, Inc. (see the SAI for a description of these situations). Unless your account is part of a tax-deferred retirement plan, an exchange is a taxable event, and you may realize a gain or a loss for tax purposes. The Fund may terminate your exchange privilege if the adviser determines t hat your exchange activity is likely to adversely impact its ability to manage the Fund. See "Fund Policy on Trading of Fund Shares" for the Fund's policy. To exchange by telephone, call 1-800-422-3737. Please have your account and taxpayer identification numbers available when calling.

You also may exchange your shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet exchanges. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

HOW TO SELL SHARES

Your financial advisor can help you determine if and when you should sell your shares. You may sell shares of the Fund on any regular business day that the NYSE is open.

When the Fund receives your sales request in "good form," shares will be sold at the next calculated net asset value. "Good form" means that the Fund's transfer agent has all information and documentation it deems necessary to effect your order. For example, when selling shares by letter of instruction, "good form" means (i) your letter has complete instructions, the proper signatures and Medallion Signature Guarantees, (ii) if applicable, you have included any certificates for shares to be sold, and (iii) any other required documents are attached. For additional documents required for sales by corporations, agents, fiduciaries, surviving joint owners and other legal entities, please call 1-800-345-6611. Retirement plan accounts have special requirements; please call 1-800-799-7526 for more information.

The Fund will generally send proceeds from the sale to you within seven days (usually on the next business day after your request is received in "good form"). However, if you purchased your shares by check, the Fund may delay sending the proceeds from the sale of your shares for up to 10 days after your purchase to protect against checks that are returned. No interest will be paid on uncashed redemption checks. Redemption proceeds may be paid in securities rather than cash, under certain circumstances. For more information, see the paragraph "Non-Cash Redemptions" under the section "How to Sell Shares" in the SAI.

During any 90-day period for any one shareholder, the Fund is obligated to redeem shares solely in cash up to the lesser of $250,000 or 1% of the Fund's net assets. Redemptions in excess of these limits will normally be paid in cash, but may be paid wholly or partly by an in-kind distribution of securities.

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Outlined below are the various options for selling shares:

Method	Instructions
Through your financial advisor	You may call your financial advisor to place your sell order. To receive the current trading day's price, your financial advisor must receive your request prior to the close of regular trading on the NYSE, usually 4:00 p.m. Eastern time. Your financial advisor may charge you fees for executing a redemption for you.
By exchange	You or your financial advisor may sell Fund shares by exchanging from the Fund into the same share class (and, in some cases, certain other classes) of another fund distributed by Columbia Management Distributors, Inc. at no additional cost. To exchange by telephone, call 1-800-422-3737.
By telephone	You or your financial advisor may sell Fund shares by telephone and request that a check be sent to your address of record by calling 1-800-422-3737, unless you have notified the Fund of an address change within the previous 30 days. The dollar limit for telephone sales is $100,000 in a 30-day period. You do not need to set up this feature in advance of your call. Certain restrictions apply to retirement accounts. For details, call 1-800-799-7526.
By mail	You may send a signed letter of instruction, if applicable, or stock power form along with any share certificates to be sold to the address below. In your letter of instruction, note the Fund's name, share class, account number, and the dollar value or number of shares you wish to sell. All account owners must sign the letter. Signatures must be guaranteed by either a bank, a member firm of a national stock exchange or another eligible guarantor that participates in the Medallion Signature Guarantee Program for amounts over $100,000 or for alternate payee or mailing instructions. Additional documentation is required for sales by corporations, agents, fiduciaries, surviving joint owners and individual retirement account owners. For details, call 1-800-345-6611. Mail your letter of instruction to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By wire	You may sell Fund shares and request that the proceeds be wired to your bank. You must set up this feature prior to your request. Be sure to complete the appropriate section of the account application for this feature. Generally, the value of your redemption must be at least equal to $500 in order to have the sale proceeds wired to your bank. There is a $7.50 charge for wiring sale proceeds to your bank. (The transfer agent may waive this fee for omnibus and nominee accounts.) Your bank may charge additional fees for such wire transfer.
By systematic withdrawal plan	You may automatically sell a specified dollar amount or percentage of your account on a monthly, quarterly or semi-annual basis and have the proceeds sent to you if your account balance is at least $5,000. The $5,000 minimum account balance requirement is waived for wrap accounts. This feature is not available if you hold your shares in certificate form. All dividend and capital gains distributions must be reinvested. Be sure to complete the appropriate section of the account application for this feature.
By electronic funds transfer	You may sell Fund shares and request that the proceeds be electronically transferred to your bank. Proceeds may take up to two business days to be received by your bank. You must set up this feature prior to your request. Be sure to complete the appropriate section of the account application for this feature.
Through the internet	You may sell Fund shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet redemptions. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

FUND POLICY ON TRADING OF FUND SHARES

The interests of the Fund's long-term shareholders may be adversely affected by certain short-term trading activity by Fund shareholders. Such short-term trading activity, when excessive, has the potential to interfere with efficient portfolio management, generate transaction and other costs, dilute the value of Fund shares held by long-term shareholders and have other adverse effects on the Fund. This type of excessive short-term trading activity is referred to herein as "market timing." For purposes of this section, the "Columbia Funds" are the Columbia, Columbia Acorn Trust and Wanger Advisors trust families of mutual funds. The Columbia Funds are not intended as vehicles for market timing. The Board of Trustees of the Fund has adopted the policies and procedures set forth below with respect to frequent trading of the Fund's shares.

The Fund, directly and through its agents, takes various steps designed to deter and curtail market timing. For example, if the Fund detects that any shareholder has conducted two "round trips" (as defined below) in the Fund

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in any 28-day period, except as noted below with respect to orders received through omnibus accounts, the Fund will reject the shareholder's future purchase orders, including exchange purchase orders, involving any Columbia fund (other than a money market fund). In addition, if the Fund determines that any person, group or account has engaged in any type of market timing activity (independent of the two-round-trip limit), the Fund may, in its discretion, reject future purchase orders by the person, group or account, including exchange purchase orders, involving the same or any other Columbia fund, and also retains the right to modify these market timing policies at any time without prior notice.

The rights of shareholders to redeem shares of the Fund are not affected by any of the limits mentioned above. However, certain funds (other than the Fund) impose a redemption fee on the proceeds of fund shares that are redeemed or exchanged within 60 days of their purchase.

For these purposes, a "round trip" is a purchase by any means into a Columbia fund followed by a redemption, of any amount, by any means out of the same Columbia fund. Under this definition, an exchange into the Fund followed by an exchange out of the Fund is treated as a single round trip. Also for these purposes, where known, accounts under common ownership or control generally will be counted together. Accounts maintained or managed by a common intermediary, such as an adviser, selling agent or trust department, generally will not be considered to be under common ownership or control.

Purchases, redemptions and exchanges made through the Columbia Funds' Automatic Investment Plan, Systematic Withdrawal Plan or similar automated plans are not subject to the two-round-trip limit. Purchases, redemptions and exchanges made by Columbia Thermostat Fund are also not subject to the two round-trip limit. The two-round-trip limit may be modified for, or may not be applied to, accounts held by certain retirement plans to conform to plan limits, considerations relating to the Employee Retirement Income Security Act of 1974 or regulations of the Department of Labor, and for certain asset allocation or wrap programs.

The practices and policies described above are intended to deter and curtail market timing in the Fund. However, there can be no assurance that these policies, individually or collectively, will be totally effective in this regard because of various factors. In particular, a substantial portion of purchase, redemption and exchange orders are received through omnibus accounts. Omnibus accounts, in which shares are held in the name of an intermediary on behalf of multiple beneficial owners, are a common form of holding shares among financial intermediaries and retirement plans. The Fund typically is not able to identify trading by a particular beneficial owner through an omnibus account, which may make it difficult or impossible to determine if a particular account is engaged in market timing. Consequently, there is the risk that the Fund may not be able to identify, deter or curtail certain market timing that occurs in the Fund, which may result in certain shareholders being able to market time the Fund while the shareholders in the Fund bear the burden of such activities.

Certain financial intermediaries (including certain retirement plan service providers whose clients include, among others, various retirement plans sponsored by Bank of America and its affiliates for the benefit of its employees (the "Bank of America retirement plan service providers")) have different policies regarding monitoring and restricting market timing in the underlying beneficial owner accounts that they maintain through an omnibus account that may be more or less restrictive than the Fund practices discussed above. In particular, the Bank of America retirement plan service providers permit the reinstatement of future purchase orders for shares of the Fund following various suspension periods. If an intermediary does not enforce the Fund's policy, the intermediary must either provide data transparency to Columbia Management or Columbia Management must

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determine that the intermediary's policy taken in its entirely provides protections to Fund shareholders that are generally commensurate with the Fund's policy.

The Fund seeks to act in a manner that it believes is consistent with the best interests of Fund shareholders in making any judgments regarding market timing. Neither the Fund nor its agents shall be held liable for any loss resulting from rejected purchase orders or exchanges.

OTHER INFORMATION ABOUT YOUR ACCOUNT

How the Fund's Share Price is Determined The price of each class of the Fund's shares is based on its net asset value. The net asset value is determined at the close of regular trading on the NYSE, usually 4:00 p.m. Eastern time, on each business day that the NYSE is open for trading (typically Monday through Friday). Net asset value is not determined on days on which the NYSE is closed for trading.

When you request a transaction, it will be processed at the net asset value per share (plus any applicable sales charges) next determined after your request is received in "good form" by the distributor. In most cases, in order to receive that day's price, the distributor must receive your order before that day's transactions are processed. If you request a transaction through your financial advisor, your financial advisor must receive your order by the close of trading on the NYSE to receive that day's price.

The Fund determines its net asset value for each share class by dividing each class's total net assets by the number of that class's outstanding shares. In determining the net asset value, the Fund must determine the value of each security in its portfolio at the close of each trading day. Because the Fund holds securities that are traded on foreign exchanges, the value of the Fund's securities may change on days when shareholders will not be able to buy or sell Fund shares. This will affect the Fund's net asset value on the day it is next determined. Securities for which market quotations are available are valued each day at the current market value. However, where market quotations are unavailable, or when the adviser believes that subsequent events have made them unreliable, the Fund may use other data to determine the fair value of the securities.

The Fund has retained an independent statistical fair value pricing service to assist in the fair valuation process for securities principally traded in a foreign market in order to adjust for possible changes in value that may occur between the close of the foreign exchange and the time at which Fund shares are priced. The use of an independent fair value pricing service is intended to and may decrease the opportunities for time zone arbitrage transactions. There can be no assurance that the use of an independent fair value pricing service will successfully decrease arbitrage opportunities. If a security is valued at a "fair value," that value may be different from the last quoted market price for the security.

You can find the daily prices of some share classes for the Fund in most major daily newspapers under the heading of "Columbia." You can find daily prices for all share classes by visiting www.columbiafunds.com.

Share Certificates Share certificates are not available for any class of shares offered by the Fund. If you currently hold previously issued share certificates, you will not be able to sell your shares until you have returned your share certificates to the transfer agent.

Dividends, Distributions, and Taxes The Fund has the potential to make the following distributions:

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Types of Distributions

Dividends	Represents interest and dividends earned from securities held by the Fund, net of expenses incurred by the Fund.
Capital gains	Represents net long-term capital gains on sales of securities held for more than one year and net short-term capital gains, which are gains on sales of securities held for a one-year period or less.

Distribution Options The Fund distributes any dividends in June and December and any capital gains (including short-term capital gains) at least annually. You can choose one of the options listed in the table below for these distributions when you open your account. To change your distribution option call 1-800-345-6611.

If you do not indicate on your application or at the time your account is established your preference for handling distributions, the Fund will automatically reinvest all distributions in additional shares of the Fund.

UNDERSTANDING FUND DISTRIBUTIONS

The Fund may earn income from the securities it holds. The Fund also may realize capital gains or losses on sales of its securities. The Fund intends to distribute substantially all of its net investment income and capital gains to shareholders each year. As a shareholder, you are entitled to a portion of the Fund's income and capital gains based on the number of shares you own at the time these distributions are declared.

Distribution Options

Reinvest all distributions in additional shares of the Fund

Reinvest all distributions in shares of another fund

Receive dividends in cash (see options below) and reinvest capital gains

Receive all distributions in cash (with one of the following options):

•  send the check to your address of record

•  send the check to a third-party address

•  transfer the money to your bank via electronic funds transfer

Distributions of $10 or less will automatically be reinvested in additional Fund shares. If you elect to receive distributions by check and the check is returned as undeliverable, all subsequent distributions will be reinvested in additional shares of the Fund.

Taxes Unless you are an entity exempt from income taxes or invest under a retirement account, regardless of whether you receive your distributions in cash or reinvest them in additional Fund shares, all Fund distributions are subject to federal income tax. Depending on where you live, distributions also may be subject to state and local income taxes.

The Fund intends to elect to be treated and to qualify each year as a regulated investment company. A regulated investment company is not subject to tax at the corporate level on income and gains from investments that are distributed to shareholders in accordance with applicable law. However, the Fund's failure to qualify as a regulated investment company could result in corporate level taxation, and consequently, a reduction in income available for distribution to shareholders.

In general, any distributions of dividends, interest and short-term capital gains (determined by how long the Fund held the investments that generated them) are taxable as ordinary income, unless such dividends are

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"qualified dividend income" (as defined in the Internal Revenue Code) eligible for a reduced rate of tax. Properly designated distributions of long-term capital gains (determined by how long the Fund held the investments that generated them) are generally taxable as such, regardless of how long you have held your Fund shares. You will be provided with information each year regarding the amount of ordinary income and capital gains distributed to you for the previous year and any portion of your distribution which is exempt from state and local taxes. Long-term capital gain rates have been reduced — in general, to 15% with lower rates applying to taxpayers in the 10% and 15% rate brackets — for taxable years beginning before January 1, 2011. Distributions are taxable to you even if they are paid from income or gains earned by the Fund before you made your investment (and thus were included in the price you paid). Your in vestment in the Fund may have additional personal tax implications. Please consult your tax advisor about foreign, federal, state, local or other applicable tax laws.

In addition to the dividends and capital gains distributions made by the Fund, you may realize a capital gain or loss when selling or exchanging shares of the Fund. Such transactions also may be subject to federal, state and local income tax.

Foreign Income Taxes The Fund may receive investment income from sources within foreign countries, and that income may be subject to foreign income taxes at the source. If the Fund pays non-refundable taxes to foreign governments during the year, the taxes will reduce the Fund's dividends but will still be included in your taxable income.

Board of Trustees

The Fund is governed by its Board of Trustees. More than 75% of the Fund's Trustees are independent, meaning that they have no affiliation with the adviser or the Funds, apart from their positions as Trustees and the personal investments they may have made as private individuals.

The independent Trustees bring backgrounds in business and the professions and academia to their task of working with the Funds' officers to establish the policies and oversee the activities of the Funds. Among the Trustees' responsibilities are selecting the investment adviser for the Funds; negotiating the advisory agreements; reviewing other contracts; approving investment policies; monitoring Fund operations, performance, and costs; and nominating or selecting new Trustees.

Each Trustee serves a Fund until his or her retirement, resignation, death or removal; or otherwise as specified in the Trust's organizational documents. It is expected that every five years the Trustees will call a meeting of shareholders to elect Trustees. A Trustee must retire at the end of the year in which he or she attains the age of 75. Any Trustee may be removed at a shareholders' meeting by a vote representing two-thirds of the net asset value of all shares of the Funds of the Trust. The mailing address for the Trustees and officers is 227W.Monroe, Suite 3000, Chicago, Illinois 60606.

For more detailed information on the Board of Trustees, please refer to the SAI.

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Managing the Fund

INVESTMENT ADVISER

Columbia Wanger Asset Management, L.P. (CWAM), located at 227 West Monroe Street, Suite 3000, Chicago, Illinois 60606, is the Fund's investment adviser and is responsible for the Fund's management, subject to the oversight of the Fund's Board of Trustees. CWAM and its predecessor have managed mutual funds, including the Fund, since 1992. In its duties as investment adviser, CWAM runs the Fund's day-to-day business, including making investment decisions and placing all orders for the purchase and sale of the Fund's portfolio securities.

CWAM was previously named Liberty Wanger Asset Management, L.P., and its predecessor was named Wanger Asset Management, L.P. (WAM). CWAM is a wholly owned subsidiary of Columbia Management Group, LLC, which is an indirect wholly owned subsidiary of Bank of America Corporation. As of December 31, 2006, CWAM managed more than $32.9 billion in assets.

CWAM's advisory fee for managing the Fund in 2006 was 0.64% of the Fund's average daily net assets. CWAM also received an administrative fee from the Fund in 2006 of 0.04% of the Fund's average daily net assets. A discussion of the factors considered by the Fund's Board of Trustees in approving the Fund's investment advisory contract is included in the Fund's annual report to shareholders for the period ended December 31, 2006.

PORTFOLIO MANAGERS

CWAM uses a team to assist the lead portfolio managers in managing the Fund. Team members share responsibility for providing ideas, information and knowledge in managing the Fund, and each team member has one or more particular areas of expertise. Portfolio managers make strategic decisions and monitor and supervise individual transactions. While certain analysts recommend transactions for approval by the portfolio managers, more seasoned analysts are authorized to buy and sell securities for the Fund within the guidelines set by portfolio managers.

Charles P. McQuaidLead portfolio manager
Charles McQuaid is president of the Trust and a member of the Trust's Board of Trustees. He has been president of CWAM since October 2003, chief investment officer of CWAM since October 2003, and was director of research at CWAM and its predecessor from July 1992 through December 2003. Mr. McQuaid has been a member of Columbia Acorn Fund's management team since 1978, co-managed Columbia Acorn Fund from 1995 through September 2003 and has been the Fund's lead portfolio manager since September 2003. He served as CWAM's interim director of international research from October 2003 to December 2004. Mr. McQuaid has been the president of Wanger Advisors Trust si nce 2003 and a trustee since September 2006. He also manages two domestic separate accounts and two offshore funds.

Robert A. MohnCo-portfolio manager
Robert Mohn is a vice president of the Trust. He has been a member of the domestic analytical team at CWAM and its predecessor since August 1992. He has managed Columbia Acorn USA since its inception in 1996, co-managed Columbia Acorn Fund since May 2003, and also manages Wanger U.S. Smaller Companies, a mutual fund underlying variable insurance products, and the U.S. fund of an investment company whose shares are offered only to non-U.S. investors. Mr. Mohn also is a vice president of Wanger Advisors Trust and the director of domestic research for CWAM.

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Managing the Fund

The SAI provides additional information about the portfolio managers' compensation, other accounts managed and ownership of securities in the Fund.

LEGAL PROCEEDINGS

The Trust, CWAM and the trustees of the Trust (collectively, the "Columbia defendants") are named as defendants in class and derivative complaints, which were consolidated in a Multi-District Action in the federal district court for the District of Maryland on February 20, 2004 (the "MDL Action"). These lawsuits contend that defendants permitted certain investors to market time their trades in certain Columbia Acorn Funds. The MDL Action is ongoing. All claims against the Trust and its independent trustees have been dismissed; however, the interested trustees of the Trust are still parties to the MDL Action.

On March 21, 2005, a class action complaint was filed against the Trust in the Superior Court of the Commonwealth of Massachusetts seeking to rescind the contingent deferred sales charges assessed upon redemption of Class B shares of Columbia Acorn Funds due to the alleged market timing of the Columbia Acorn Funds. In addition to the rescission of sales charges, plaintiffs seek recovery of actual damages, attorneys' fees and costs. The case has been transferred to the MDL Action in the federal district court of Maryland.

The Trust and CWAM are also defendants in a class action lawsuit, filed on November 13, 2003 in the Circuit Court of the Third Judicial Circuit, Madison County, Illinois, that alleges, in summary, that the Trust and CWAM exposed shareholders of Columbia Acorn International to trading by market timers by allegedly (a) failing to properly evaluate daily whether a significant event affecting the value of that fund's securities had occurred after foreign markets had closed but before the calculation of the fund's net asset value; (b) failing to implement the fund's portfolio valuation and share pricing policies and procedures; and (c) failing to know and implement applicable rules and regulations concerning the calculation of net asset value ("Fair Valuation Lawsuit"). On April 5, 2005, the United States Court of Appeals for the Seventh Circuit ruled that the plaintiffs' state law claims were preempted under federal law resulting in the dismissal of plaintiffs' complaint. Plaintiffs appealed the Seventh Circuit's ruling to the United States Supreme Court. On June 15, 2006, the Supreme Court reversed the Seventh Circuit's ruling on jurisdictional grounds, and the case ultimately was remanded to the state court.

On April 4, 2006, the plaintiffs and the Columbia defendants named in the MDL Action executed an agreement in principle intended to fully resolve all of the lawsuits consolidated in the MDL Action as well as the Fair Valuation Lawsuit. The court entered a stay after the parties executed the agreement in principle. The settlement is subject to court approval.

In 2004, CWAM and the trustees of the Columbia Acorn Trust were named as defendants in certain purported shareholder class and derivative actions making claims, including claims under the Investment Company and the Investment Advisers Acts of 1940 and state law. Certain Columbia Acorn Funds were named as nominal defendants. The suits allege, inter alia, that the fees and expenses paid by the funds are excessive and that the funds' advisers and their affiliates inappropriately used fund assets to distribute the funds and for other improper purposes. On March 2, 2005, the actions were consolidated in the Massachusetts federal court as In re Columbia Entities Litigation. The plaintiffs filed a consolidated amended complaint on June 9, 2005. On November 30, 2005, the judge dismissed all claims by plaintiffs and entered final judgment in favor of the defendants. The plaintiffs appealed to the United States Court of Appeals for the First Circuit on December 30, 2005. A stipulation and settlement agreement dated January 19, 2007 was filed in the First Circuit on February 14, 2007, with a joint stipulation of dismissal and motion for remand to obtain district court approval of the settlement. The joint

23

Managing the Fund

motion was granted and the appeal was dismissed. On March 6, 2007, the case was remanded to the District Court, where the parties will seek court approval of the settlement. The terms of the proposed settlement, if approved, will require payments by the funds' adviser and/or its affiliates, including payment of plaintiffs' attorneys' fees and notice to class members. In the event that the settlement is not approved, the plaintiffs may elect to go forward with their appeal and no opinion is expressed regarding the likely outcome or financial impact of such an appeal on any fund.

On or about January 11, 2005, a putative class action lawsuit was filed in federal district court in Massachusetts against the Trust and its trustees, along with Columbia Management Advisors, LLC, the sub-administrator of the Wanger Advisors Funds and the Columbia Acorn Funds. The plaintiffs allege that the defendants failed to submit Proof of Claims in connection with settlements of securities class action lawsuits filed against companies in which the Columbia Acorn Funds held positions. The complaint seeks compensatory and punitive damages, and the disgorgement of all fees paid to the Columbia Management Advisors, LLC. Plaintiffs have voluntarily dismissed the Trust and its independent trustees.

The Trust and CWAM intend to defend these suits vigorously.

As a result of these matters or any adverse publicity or other developments resulting from them, there may be increased redemptions or reduced sales of Fund shares, which could increase transaction costs or operating expenses, or have other adverse consequences for the Fund.

However, based on currently available information, the Trust believes that the likelihood that these lawsuits will have a material adverse impact on any fund is remote, and CWAM believes that the lawsuits are not likely to materially affect its ability to provide investment management services to the Fund.

Other Investment Strategies and Risks

The Fund's principal investment strategies and associated risks are described under "The Fund — Principal Investment Strategies" and "The Fund — Principal Investment Risks." This section describes other investments the Fund may make and the risks associated with them. In seeking to achieve its investment goal, the Fund may invest in various types of securities and engage in various investment techniques, which are not the principal focus of the Fund and therefore are not described in this prospectus. These types of securities and investment practices and their associated risks are identified and discussed in the Fund's SAI, which you may obtain free of charge (see back cover). The adviser may elect not to buy any of these securities or use any of these techniques. The Fund may not always achieve its investment goal. Except as otherwise noted, approval by the Fund's shareholders is not required to modify or change the F und's investment strategies.

THE INFORMATION EDGE

The Fund generally invests in entrepreneurially managed smaller- and mid-sized companies that it believes are not as well known by financial analysts and whose position in a niche creates the opportunity for superior earnings-growth potential. CWAM may identify what it believes are important economic, social or technological trends (for example, the growth of outsourcing as a business strategy, or the productivity gains from the increasing use of technology) and try to identify companies it thinks will benefit from these trends.

24

Other Investment Strategies and Risks

In making investments for the Fund, CWAM relies primarily on independent, internally generated research to uncover companies that may be less well known than the more popular names. To find these companies, CWAM compares growth potential, financial strength and fundamental value among companies.

Growth Potential	Financial Strength	Fundamental Value
• superior technology • innovative marketing • managerial skill • market niche • good earnings prospects • strong demand for product	• low debt • adequate working capital • conservative accounting practices • adequate profit margin	• reasonable stock price relative to growth potential and financial strength • valuable assets
The realization of this growth potential would likely produce superior performance that is sustainable over time.	A strong balance sheet gives management greater flexibility to pursue strategic objectives and is important to maintaining a competitive advantage.	Once CWAM uncovers an attractive company, it identifies a price that it believes would also make the stock a good value.

LONG-TERM INVESTING

CWAM's analysts continually screen companies and make contact with more than 1,000 companies around the globe each year. To accomplish this, CWAM analysts often talk directly to top management, vendors, suppliers and competitors.

In managing the Fund, CWAM tries to maintain lower taxes and transaction costs by investing with a long-term time horizon (at least two to five years). However, securities purchased on a long-term basis may be sold within 12 months after purchase due to changes in the circumstances of a particular company or industry, or changes in general market or economic conditions.

DERIVATIVE STRATEGIES

The Fund may enter into a number of derivative strategies, including those that employ futures, options, straddles or similar transactions, to gain or reduce exposure to particular securities or markets. These strategies, commonly referred to as derivatives, involve the use of financial instruments whose values depend on, or are derived from, the value of an underlying security, index or currency. The Fund may use these strategies to adjust the Fund's sensitivity to changes in interest rates, or for other hedging purposes (i.e., attempting to offset a potential loss in one position by establishing an interest in an opposite position). Derivative strategies involve the risk that they may exaggerate a loss, potentially losing more money than the actual cost of the underlying security, or limit a potential gain. Also, with some derivative strategies there is a risk that the other party to the transaction may fail to honor its contr act terms, causing a loss to the Fund or that the Fund may not be able to find a suitable derivative transaction counterparty, and thus may be unable to invest in derivatives altogether.

25

Other Investment Strategies and Risks

TEMPORARY DEFENSIVE STRATEGIES

At times, CWAM may determine that adverse market conditions make it desirable to temporarily suspend the Fund's normal investment activities. During such times, the Fund may, but is not required to, invest in cash or high-quality, short-term debt securities, without limit. Taking a temporary defensive position may prevent the Fund from achieving its investment goal.

26

Financial Highlights

The financial highlights table is intended to help you understand the Fund's financial performance. Information is shown for the Fund's last five fiscal years, which run from January 1 to December 31. Certain information in the table reflects the financial results for a single Class A, B or C share. The total returns in the table represent the return that you would have earned (or lost) on an investment in the Fund (assuming reinvestment of all dividends and distributions). This information has been derived from the Fund's financial statements, which have been audited for the years ended December 31, 2004, 2005 and 2006 by PricewaterhouseCoopers LLP, an independent registered public accounting firm, whose report, along with the Fund's financial statements, is included in the Fund's annual report. The information for the years ended December 31, 2002 and 2003 is included in the Fund's financial statements that have been audited b y another independent registered public accounting firm, whose report expressed an unqualified opinion on those financial statements and highlights. You can request a free annual report containing those financial statements by calling 1-800-345-6611.

Columbia Acorn Fund

	Year Ended December 31,
	2006			2005			2004			2003			2002
	Class A			Class A			Class A			Class A			Class A
Net asset value — Beginning of period ($)		27.57			25.93			22.20			15.34			17.80
Income from Investment Operations ($):
Net investment income (loss)(a)		0.05			0.07			(0.05	)		(0.07	)		(0.07	)
Net realized and unrealized gain (loss)		3.82			3.20			4.69			6.95			(2.39	)
Total from Investment Operations		3.87			3.27			4.64			6.88			(2.46	)
Less Distributions Declared to Shareholders ($):
From net investment income		(0.04	)		(0.07	)		—			—			—
From net realized gains		(2.38	)		(1.56	)		(0.91	)		(0.02	)		—
Total Distributions Declared to Shareholders		(2.42	)		(1.63	)		(0.91	)		(0.02	)		—
Net asset value — End of period ($)		29.02			27.57			25.93			22.20			15.34
Total return (%)(b)		14.13	(c)		12.76	(c)		21.05	(c)		44.85			(13.82	)
Ratios to Average Net Assets/Supplemental Data (%):
Expenses(d)		1.02			1.03			1.20			1.33			1.42
Net investment income (loss)(d)		0.17			0.28			(0.21	)		(0.36	)		(0.45	)
Waiver/reimbursement		0.02			0.02			0.02			—			—
Portfolio turnover rate (%)		22			16			20			10			13
Net assets at end of period (000's) ($)		4,067,868			3,349,461			2,669,936			1,982,260			724,121

(a)  Per share data was calculated using average shares outstanding during the period.

(b)  Total return at net asset value assuming all distributions reinvested and no initial sales charge or contingent deferred sales charge.

(c)  Had the investment adviser and/or transfer agent not waived and/or reimbursed a portion of expenses, total return would have
been reduced.

(d)  The benefits derived from custody fees paid indirectly had no impact.

27

Financial Highlights

Columbia Acorn Fund

	Year Ended December 31,
	2006			2005			2004			2003			2002
	Class B			Class B			Class B			Class B			Class B
Net asset value — Beginning of period ($)		26.61			25.19			21.75			15.13			17.67
Income from Investment Operations ($):
Net investment loss(a)		(0.13	)		(0.11	)		(0.22	)		(0.18	)		(0.17	)
Net realized and unrealized gain (loss)		3.68			3.09			4.57			6.82			(2.37	)
Total from Investment Operations		3.55			2.98			4.35			6.64			(2.54	)
Less Distributions Declared to Shareholders ($):
From net realized gains		(2.38	)		(1.56	)		(0.91	)		(0.02	)		—
Total Distributions Declared to Shareholders		(2.38	)		(1.56	)		(0.91	)		(0.02	)		—
Net asset value — End of period ($)		27.78			26.61			25.19			21.75			15.13
Total return (%)(b)		13.43	(c)		11.98	(c)		20.15	(c)		43.89			(14.37	)
Ratios to Average Net Assets/Supplemental Data(%):
Expenses(d)		1.66			1.72			1.95			1.98			2.07
Net investment loss(d)		(0.48	)		(0.42	)		(0.96	)		(1.01	)		(1.10	)
Waiver/reimbursement		0.02			0.02			0.02			—			—
Portfolio turnover rate (%)		22			16			20			10			13
Net assets at end of period (000's) ($)		1,404,165			1,422,580			1,399,135			1,221,931			618,727

(a)  Per share data was calculated using average shares outstanding during the period.

(b)  Total return at net asset value assuming all distributions reinvested and no initial sales charge or contingent deferred sales charge.

(c)  Had the investment adviser and/or transfer agent not waived and/or reimbursed a portion of expenses, total return would have
been reduced.

(d)  The benefits derived from custody fees paid indirectly had no impact.

28

Financial Highlights

Columbia Acorn Fund

	Year Ended December 31,
	2006			2005			2004			2003			2002
	Class C			Class C			Class C			Class C			Class C
Net asset value — Beginning of period ($)		26.58			25.18			21.75			15.12			17.66
Income from Investment Operations ($):
Net investment loss(a)		(0.17	)		(0.13	)		(0.22	)		(0.18	)		(0.17	)
Net realized and unrealized gain (loss)		3.67			3.09			4.56			6.83			(2.37	)
Total from Investment Operations		3.50			2.96			4.34			6.65			(2.54	)
Less Distributions Declared to Shareholders ($):
From net realized gains		(2.38	)		(1.56	)		(0.91	)		(0.02	)		—
Total Distributions Declared to Shareholders		(2.38	)		(1.56	)		(0.91	)		(0.02	)		—
Net asset value — End of period ($)		27.70			26.58			25.18			21.75			15.12
Total return (%)(b)		13.25	(c)		11.90	(c)		20.11	(c)		43.99			(14.38	)
Ratios to Average Net Assets/Supplemental Data(%):
Expenses(d)		1.80			1.82			1.95			1.98			2.07
Net investment income loss(d)		(0.61	)		(0.51	)		(0.96	)		(1.01	)		(1.10	)
Waiver/reimbursement		0.02			0.02			0.02			—			—
Portfolio turnover rate (%)		22			16			20			10			13
Net assets at end of period (000's) ($)		1,345,520			1,220,339			1,083,006			900,016			376,024

(a)  Per share data was calculated using average shares outstanding during the period.

(b)  Total return at net asset value assuming all distributions reinvested and no initial sales charge or contingent deferred sales charge.

(c)  Had the investment adviser and/or transfer agent not waived and/or reimbursed a portion of expenses, total return would have
been reduced.

(d)  The benefits derived from custody fees paid indirectly had no impact.

29

Appendix

Hypothetical Investment and Expense Information

The Fund is required to disclose the following supplemental hypothetical investment information, which provides additional information about the effect of the expenses paid by the Fund, including investment advisory fees and other Fund costs, on the Fund's returns over a 10-year period. The tables show the estimated expenses that would be charged on a hypothetical investment of $10,000 in each class of the Fund assuming a 5% return each year, the cumulative return after fees and expenses, and the hypothetical year-end balance after fees and expenses. The tables also assume that all dividends and distributions are reinvested and that Class B shares convert to Class A shares after eight years. The annual expense ratios used for the Fund, which are the same as those stated in the Annual Fund Operating Expenses table, are presented in the tables, and are net of any contractual fee waivers or expense reimbursements for the period of the contractual commitment. Your actual costs may be higher or lower. The tables shown below reflect the maximum initial sales charges for Class A shares but do not reflect any contingent deferred sales charges which may be payable on redemption. If contingent deferred sales charges were reflected, the "Hypothetical Year-End Balance After Fees and Expenses" amounts shown would be lower and the "Annual Fees and Expenses" amounts shown would be higher. As noted previously, the Fund's minimum investment for initial purchases or exchanges is $75,000.

Columbia Acorn Fund — Class A Shares

Maximum Sales Charge 5.75%					Initial Hypothetical Investment Amount $10,000.00						Assumed Rate of Return 5%
Year		Cumulative Return Before Fees & Expenses			Annual Expense Ratio			Cumulative Return After Fees & Expenses			Hypothetical Year-End Balance After Fees & Expenses		Annual Fees & Expenses(1)
	1		5.00	%		1.05	%		-2.03	%(2)	$	9,797.29	$	675.92
	2		10.25	%		1.05	%		1.84	%	$	10,184.28	$	104.90
	3		15.76	%		1.05	%		5.87	%	$	10,586.56	$	109.05
	4		21.55	%		1.05	%		10.05	%	$	11,004.73	$	113.35
	5		27.63	%		1.05	%		14.39	%	$	11,439.42	$	117.83
	6		34.01	%		1.05	%		18.91	%	$	11,891.27	$	122.49
	7		40.71	%		1.05	%		23.61	%	$	12,360.98	$	127.32
	8		47.75	%		1.05	%		28.49	%	$	12,849.24	$	132.35
	9		55.13	%		1.05	%		33.57	%	$	13,356.78	$	137.58
	10		62.89	%		1.05	%		38.84	%	$	13,884.37	$	143.02
Total Gain After Fees and Expenses											$	3,884.37
Total Annual Fees and Expenses													$	1,783.81

(1)   Annual Fees and Expenses are calculated based on the average between the beginning and ending balance for each year. All information is calculated on an annual compounding basis.

(2)   Reflects deduction of the maximum initial sales charge.

30

Appendix

Columbia Acorn Fund — Class B Shares

Maximum Sales Charge 0.00%					Initial Hypothetical Investment Amount $10,000.00						Assumed Rate of Return 5%
Year		Cumulative Return Before Fees & Expenses			Annual Expense Ratio			Cumulative Return After Fees & Expenses			Hypothetical Year-End Balance After Fees & Expenses		Annual Fees & Expenses(1)
	1		5.00	%		1.63	%		3.37	%	$	10,337.00	$	165.75
	2		10.25	%		1.63	%		6.85	%	$	10,685.36	$	171.33
	3		15.76	%		1.63	%		10.45	%	$	11,045.45	$	177.11
	4		21.55	%		1.63	%		14.18	%	$	11,417.69	$	183.07
	5		27.63	%		1.63	%		18.02	%	$	11,802.46	$	189.24
	6		34.01	%		1.63	%		22.00	%	$	12,200.20	$	195.62
	7		40.71	%		1.63	%		26.11	%	$	12,611.35	$	202.21
	8		47.75	%		1.63	%		30.36	%	$	13,036.35	$	209.03
	9		55.13	%		1.05	%		35.51	%	$	13,551.29	$	139.59
	10		62.89	%		1.05	%		40.87	%	$	14,086.57	$	145.10
Total Gain After Fees and Expenses											$	4,086.57
Total Annual Fees and Expenses													$	1,778.05

(1)   Annual Fees and Expenses are calculated based on the average between the beginning and ending balance for each year. All information is calculated on an annual compounding basis.

31

Appendix

Columbia Acorn Fund — Class C Shares

Maximum Sales Charge 0.00%					Initial Hypothetical Investment Amount $10,000.00						Assumed Rate of Return 5%
Year		Cumulative Return Before Fees & Expenses			Annual Expense Ratio			Cumulative Return After Fees & Expenses			Hypothetical Year-End Balance After Fees & Expenses		Annual Fees & Expenses(1)
	1		5.00	%		1.84	%		3.16	%	$	10,316.00	$	186.91
	2		10.25	%		1.84	%		6.42	%	$	10,641.99	$	192.81
	3		15.76	%		1.84	%		9.78	%	$	10,978.27	$	198.91
	4		21.55	%		1.84	%		13.25	%	$	11,325.19	$	205.19
	5		27.63	%		1.84	%		16.83	%	$	11,683.06	$	211.68
	6		34.01	%		1.84	%		20.52	%	$	12,052.25	$	218.36
	7		40.71	%		1.84	%		24.33	%	$	12,433.10	$	225.27
	8		47.75	%		1.84	%		28.26	%	$	12,825.98	$	232.38
	9		55.13	%		1.84	%		32.31	%	$	13,231.28	$	239.73
	10		62.89	%		1.84	%		36.49	%	$	13,649.39	$	247.30
Total Gain After Fees and Expenses											$	3,649.39
Total Annual Fees and Expenses													$	2,158.54

(1)   Annual Fees and Expenses are calculated based on the average between the beginning and ending balance for each year. All information is calculated on an annual compounding basis.

32

Notes

33

Notes

34

FOR MORE INFORMATION

Additional information about the Fund's investments is available in the Fund's semiannual and annual reports to shareholders. The annual report contains a discussion of the market conditions and investment strategies that significantly affected the Fund's performance during its last fiscal year.

You may wish to read the SAI for more information on the Fund and the securities in which it invests. The SAI is incorporated into this prospectus by reference, which means that it is considered to be part of this prospectus.

You can get free copies of annual and semiannual reports and the SAI, request other information and discuss your questions about the Fund by visiting www.columbiafunds.com or by writing or calling the Fund's transfer agent at:

Columbia Management Services, Inc.
P.O. Box 8081
Boston, MA 02266-8081
1-800-345-6611

Text-only versions of all Fund documents can be viewed online or downloaded from the EDGAR database on the Securities and Exchange Commission internet site at www.sec.gov.

You can review and copy information about the Fund, including the SAI, by visiting the following location, and you can obtain copies upon payment of a duplicating fee, by electronic request at the e-mail address publicinfo@sec.gov or by writing the:

Public Reference Room
Securities and Exchange Commission
Washington, DC 20549-0102

Information on the operation of the Public Reference Room may be obtained by calling 1-202-942-8090.

Investment Company Act file number:
Columbia Acorn Trust: 811-01829
•  Columbia Acorn Fund

©2007 Columbia Management Distributors, Inc.
One Financial Center, Boston, MA 02111-2621
800.426.3750 www.columbiafunds.com

INT-36/130116-0507

Columbia^SM

Acorn^® Fund  Prospectus, May 1, 2007

Class Z Shares

Advised by Columbia Wanger Asset Management, L.P.

TABLE OF CONTENTS

THE FUND	2
Investment Goal	2
Principal Investment Strategies	2
Principal Investment Risks	2
Portfolio Holdings Disclosure	3
Performance History	4
Your Expenses	5
YOUR ACCOUNT	7
How to Buy Shares	7
Eligible Investors	8
Sales Charges (Commissions)	10
How to Exchange Shares	10
How to Sell Shares	11
Fund Policy on Trading of Fund Shares	12
Financial Intermediary Payments	13
Other Information About Your Account	14
BOARD OF TRUSTEES	17
MANAGING THE FUND	17
Investment Adviser	17
Portfolio Managers	17
Legal Proceedings	18
OTHER INVESTMENT STRATEGIES AND RISKS	20
The Information Edge	20
Long-Term Investing	20
Derivative Strategies	21
Temporary Defensive Strategies	21
FINANCIAL HIGHLIGHTS	22
APPENDIX	23

Only eligible investors may purchase Class Z shares. See "Your Account — Eligible Investors" for more information.

Although these securities have been registered with the Securities and Exchange Commission, the Commission has not approved or disapproved any shares offered in this prospectus or determined whether this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Acorn^® is a trademark owned and registered by Columbia Acorn Trust, Columbia, Columbia Management^® and Columbia Management Services, Inc. are service marks owned and/or registered by Bank of America

The Fund

INVESTMENT GOAL

Columbia Acorn Fund (Acorn^® Fund) seeks to provide long-term growth of capital.

PRINCIPAL INVESTMENT STRATEGIES

Acorn Fund generally invests in the stocks of small- and medium-sized companies. The Fund generally invests in the stocks of companies with market capitalizations of less than $5 billion at the time of initial purchase. As long as a stock continues to meet the Fund's other investment criteria, the Fund may choose to hold a stock even if the issuing company's capitalization grows beyond a $5 billion capitalization.

Acorn Fund believes that these smaller companies, which are not as well known by financial analysts, may offer higher return potential than the stocks of larger companies.

Acorn Fund typically looks for companies with:

•  A strong business franchise that offers growth potential.

•  Products and services that give a company a competitive advantage.

•  A stock price the Fund's investment adviser believes is reasonable relative to the assets and earning power of the company.

Acorn Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its assets in companies outside the United States in developed markets (for example, Japan, Canada and the United Kingdom) and emerging markets (for example, Mexico, Brazil and Korea).

Additional strategies that are not principal investment strategies and the risks associated with them are described later in this prospectus under "Other Investment Strategies and Risks."

PRINCIPAL INVESTMENT RISKS

The principal risks of investing in the Fund are described below. There are many circumstances (including additional risks that are not described here) that could prevent the Fund from achieving its investment goal. You may lose money by investing in the Fund.

Management risk means that the adviser's investment decisions might produce losses or cause the Fund to underperform when compared to other funds with a similar investment goal. Market risk means that security prices in a market, sector or industry may fall, reducing the value of your investment. Because of management and market risk, there is no guarantee that the Fund will achieve its investment goal or perform favorably among comparable funds.

Since the Fund purchases equity securities, it is subject to equity risk. This is the risk that stock prices will fall over short or extended periods of time. Although the stock market historically has outperformed other asset classes over the long term, the stock market tends to move in cycles. Individual stock prices may fluctuate drastically from day-to-day and may underperform other asset classes over an extended period of time. Individual companies may report poor results or be negatively affected by industry and/or economic trends and developments. The prices of securities issued by such companies may suffer a decline in response. These price movements may result from factors affecting individual companies, industries or the securities market as a whole.

2

The Fund

Because the Fund invests in stocks, the price of its shares — its net asset value (NAV) per share — fluctuates daily in response to changes in the market value of stocks.

Sector risk is inherent in the Fund's investment strategy. Companies that are in different but closely related industries are sometimes described as being in the same broad economic sector. The values of stocks of different companies in a market sector may be similarly affected by particular economic or market events. Although the Fund does not intend to focus on any particular sector, at times the Fund may have a large portion of its assets invested in a particular sector.

Foreign securities are subject to special risks. Foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the dollar value of foreign securities denominated in foreign currencies and U.S. dollars, without a change in the intrinsic value of those securities. The liquidity of foreign securities may be more limited than that of domestic securities, which means that the Fund may, at times, be unable to sell foreign securities at desirable prices. Brokerage commissions, custodial fees and other fees are generally higher for foreign investments. In addition, foreign governments may impose withholding taxes that would reduce the amount of income and capital gains available to distribute to shareholders. Other risks include possible delays in the settlement of transactions or in the notification of income; less publicly av ailable information about companies; the impact of political, social or diplomatic events; possible seizure, expropriation or nationalization of the company or its assets; and possible imposition of currency exchange controls.

Investments in emerging markets are subject to additional risk. The risks of foreign investments are typically increased in less developed countries, which are sometimes referred to as emerging markets. For example, political and economic structures in these countries may be new and developing rapidly, which may cause instability. These countries are also more likely to experience high levels of inflation, deflation or currency devaluations, which could hurt their economies and securities markets.

Small- or mid-cap companies may be more susceptible to market downturns, and their prices could be more volatile than large-cap companies. These companies are more likely than larger companies to have limited product lines, operating histories, markets or financial resources. They may depend heavily on a small management team and may trade less frequently, may trade in smaller volumes and may fluctuate more sharply in price than stocks of larger companies. In addition, such companies may not be widely followed by the investment community, which can lower the demand for their stocks.

An investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PORTFOLIO HOLDINGS DISCLOSURE

A description of the Fund's policies and procedures with respect to the disclosure of its portfolio securities is available in the Fund's Statement of Additional Information (SAI), which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611.

The Fund posts its complete portfolio holdings as of month-end at www.columbiafunds.com approximately 30-40 calendar days after such month-end. Additionally, the Fund discloses its top 15 month-end portfolio holdings at www.columbiafunds.com on or about 15 calendar days following such month-end.

Once posted, the above information will remain available on the website until at least the date on which the Fund files a Form N-CSR or Form N-Q for the period that includes the date as of which the information is current.

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The Fund

PERFORMANCE HISTORY

The bar chart below shows the Fund's calendar-year total returns (before taxes) for its Class Z shares. The performance table following the bar chart shows how the Fund's average annual total returns for Class Z shares compare with broad measures of market performance for one year, five years and ten years. The chart and table are intended to illustrate some of the risks of investing in the Fund by showing changes in the Fund's performance from year to year. All returns include the reinvestment of dividends and distributions. As with all mutual funds, past performance (before and after taxes) does not predict the Fund's future performance.

UNDERSTANDING PERFORMANCE

Calendar Year Total Returns show the Fund's Class Z share performance for each of the last ten complete calendar years. Those returns include the effects of Fund expenses.

Average Annual Total Returns are a measure of the Fund's Class Z average performance over the past one-year, five-year and ten-year periods. They include the effects of Fund expenses.

The Fund's returns are compared to the Russell 2500 Index (Russell 2500), the Standard & Poor's 500 Index (S&P 500 Index) and the Russell 2000^® Index (Russell 2000^®). The Russell 2500, the Fund's primary benchmark, is a market-weighted index of the 2500 smallest companies that is formed by taking the 3000 largest U.S. companies and eliminating the largest 500 of those companies. The S&P 500 Index is a broad market-weighted average of 500 widely-held, large capitalization U.S. stocks. The Russell 2000^® is a market-weighted index of the 2000 smallest companies of the 3000 largest U.S. companies based on market capitalization. All third-party trademarks are the property of their owners. Unlike the Fund, indices are not investments, do not incur fees, expenses or taxes, and are not professionally managed.

Calendar Year Total Returns (Class Z)

For period shown in bar chart:
Best quarter: 4th quarter 1999, +21.94%
Worst quarter: 3rd quarter 1998, -19.51%

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The Fund

After tax returns are calculated using the highest historical individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on each investor's own tax situation and may differ from those shown. After-tax returns may not be relevant to investors who hold Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Average Annual Total Returns — for periods ended December 31, 2006

Share Class	1 Year		5 Years		10 Years
Class Z (%)
Return Before Taxes		14.45		14.71		15.16
Return After Taxes on Distributions		12.95		14.07		13.52
Return After Taxes on Distributions and Sale of Fund Shares		11.04		12.85		12.80
Indices
Russell 2500 (%)		16.17		12.19		11.26
S&P 500 Index (%)		15.79		6.19		8.42
Russell 2000® (%)		18.37		11.39		9.44

YOUR EXPENSES

Expenses are one of several factors to consider before you invest in a mutual fund. The tables below describe the fees and expenses you may pay when you buy, hold and sell shares of the Fund.

UNDERSTANDING EXPENSES

Annual Fund Operating Expenses are paid by the Fund. They include management and administration fees and other expenses that generally include, but are not limited to, transfer agency, custody, and legal fees as well as costs related to state registration and printing of Fund documents. The specific fees and expenses that make up the Fund's other expenses will vary from time to time and may include fees or expenses not described here. The Fund will likely incur portfolio transaction costs that are in addition to the total annual fund operating expenses disclosed in the fee table. These transaction costs are made up of all costs that are associated with trading securities for the Fund's portfolio and include, but are not limited to, brokerage commissions and market spreads, as well as potential changes to the price of a security due to the Fund's effor ts to purchase or sell it. While certain elements of transaction costs are readily identifiable and quantifiable, other elements that can make up a significant amount of the Fund's transaction costs are not. Higher transaction costs reduce the Fund's returns.

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The Fund

Shareholder Fees (commissions paid directly from your investment)

Maximum sales charge (load) on purchases (%) (as a percentage of the offering price)	None
Maximum deferred sales charge (load) on redemptions (%) (as a percentage of the lesser of purchase price or redemption price)	None
Redemption fee (%) (as a percentage of amount redeemed, if applicable)	None(1)

(1)   There is a $7.50 charge for wiring sale proceeds to the transfer agent.

Annual Fund Operating Expenses (deducted directly from Fund assets)

Management fees(1) (%)	0.64
Distribution and service (12b-1) fees (%)	None
Other expenses(2) (%)	0.11
Total annual fund operating expenses (%)	0.75

(1)  The Fund pays an investment advisory fee of 0.64%. The Fund and its adviser have implemented a breakpoint schedule for the Fund's investment advisory fees. The investment advisory fee rates charged to the Fund will decline as Fund assets grow and will continue to be based on a percentage of the Fund's average daily assets. The annual fee schedule for the Fund is as follows: 0.74% for assets up to $700 million; 0.69% for assets in excess of $700 million and up to $2 billion; 0.64% for assets in excess of $2 billion and up to $6 billion; and 0.63% for assets in excess of $6 billion. In addition to the management fee, the Fund and the other funds of Columbia Acorn Trust (the "Trust") pay the adviser an administrative fee based on the average daily aggregate net assets of the Trust at the following annual rates: 0.05% of net assets up to $8 billion; 0.04% of the next $8 billion; and 0.03% of net assets in excess of $1 6 billion. Based on the Trust's average daily net assets as of December 31, 2006, the administrative fee would be at a rate of 0.04% and is included in "Other expenses."

(2)  "Other expenses" have been restated to reflect contractual changes to the transfer agency fees paid by the Fund.

Example Expenses help you compare the cost of investing in the Fund to the cost of investing in other mutual funds. It uses the following hypothetical conditions:

•  $10,000 initial investment^†

•  5% total return for each year

•  Fund operating expenses remain the same

•  Reinvestment of all dividends and distributions

†  For example only since the minimum initial investment in the Fund is $75,000, subject to certain exceptions described in the section "Eligible Investors" beginning on page 8.

Example Expenses for a $10,000 investment (your actual costs may be higher or lower)

1 Year		3 Years		5 Years		10 Years
$	77	$	240	$	417	$	930

See the Appendix for additional hypothetical investment and expense information.

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HOW TO BUY SHARES

If you are an eligible investor (described on page 8), when the Fund receives your purchase request in "good form," your shares will be bought at the next calculated price. "Good form" means that the Fund's transfer agent has all information and documentation it deems necessary to effect your order. For example "good form" may mean that you have properly placed your order with Columbia Management Services, Inc. or your financial advisor or the Fund's transfer agent has received your completed application, including all necessary signatures. The Fund reserves the right to refuse a purchase order for any reason, including if the Fund believes that doing so would be in the best interest of the Fund and its shareholders. The USA PATRIOT Act may require us to obtain personal information from you that we will use to verify your identity. If you do not provide the information, we may not be able to open your account. If we are unable t o verify your customer information, we reserve the right to close your account or take such other steps as we deem reasonable.

You or your financial advisor may acquire shares of the Fund for your account by exchanging shares you own in a different fund distributed by Columbia Management Distributors, Inc. for shares of the same class or Class A of the Fund at no additional cost. To exchange by telephone, call 1-800-422-3737. Please see "How to Exchange Shares" for more information.

Outlined below are the various options for buying shares:

Method	Instructions
Through your financial advisor	Your financial advisor can help you establish your account and buy Fund shares on your behalf. To receive the current trading day's price, your financial advisor must receive your request prior to the close of regular trading on the New York Stock Exchange (NYSE), usually 4:00 p.m. Eastern time. Your financial advisor may charge you fees for executing the purchase for you.
By check (new account)	For new accounts, send a completed application and check made payable to the Fund to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By check (existing account)	For existing accounts, fill out and return the additional investment stub included in your account statement, or send a letter of instruction including the name, Fund share class and account number with a check made payable to the Fund to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By exchange	You may acquire Fund shares for your account by exchanging shares you own in a different fund distributed by Columbia Management Distributors, Inc. for shares of the same class or Class A of the Fund at no additional cost. To exchange by telephone, call 1-800-422- 3737. Please see "How to Exchange Shares" for more information.
By wire	You may purchase Fund shares by wiring money from your bank account to your Fund account. To wire funds to your Fund account, call 1-800-422-3737 for wiring instructions.
By electronic funds transfer	You may purchase Fund shares by electronically transferring money from your bank account to your Fund account by calling 1-800-422-3737. An electronic funds transfer may take up to two business days to settle and must be considered in "good form." You must set up this feature prior to your telephone request. Be sure to complete the appropriate section of the application for this feature.
Automatic investment plan	You may make monthly or quarterly investments ($50 minimum) automatically from your bank account to your Fund account. You may select a pre-authorized amount to be sent via electronic funds transfer. Be sure to complete the appropriate section of the application for this feature.
Automated dollar cost averaging	You may purchase Fund shares for your account by exchanging $100 or more each month from another fund for shares of the same class of the Fund at no additional cost. Exchanges will continue so long as your fund balance is sufficient to complete the transfers. You may terminate your program or change the amount of the exchange (subject to the $100 minimum) by calling 1-800-345-6611. Be sure to complete the appropriate section of the account application for this feature.

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Your Account

Method	Instructions
By dividend diversification	You may automatically invest dividends distributed by another fund into the same class of shares of the Fund at no additional sales charge. There may be an additional sales charge if automatically investing dividends from a money market fund. To invest your dividends in the Fund, call 1-800-345-6611.
Through the internet	You may purchase Fund shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet purchases. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

ELIGIBLE INVESTORS

Only certain eligible investors may purchase Class Z shares of the Fund (Eligible Investor), directly or by exchange. Please read the following section for a more detailed description of the eligibility requirements. The Eligible Investors described below are subject to different minimum initial investment requirements.

Eligibility for certain waivers, exemptions or share classes by new or existing investors may not be readily available or accessible through all intermediaries or all types of accounts offered by a broker-dealer, bank, third- party administrator or other financial institution (each commonly referred to as an "intermediary"). Accessibility of these waivers through a particular intermediary also may change at any time. If you believe you are eligible to purchase shares under a specific exemption, but are not permitted by your intermediary to do so, please contact your intermediary. You may be asked to provide information, including account statements and other records, regarding your eligibility.

Eligible Investors and their applicable investment minimums are as follows:

No minimum initial investment

•  Any trustee or director (or family member) of Columbia Acorn Trust;

•  Any employee (or family member) of Columbia Wanger Asset Management, L.P.; or

•  Any group retirement plan, holding Fund shares in an omnibus manner, for which an intermediary or other entity provides services and is not compensated by the Funds for those services, other than payments for shareholder servicing or sub-accounting performed in place of the transfer agent.

$75,000 minimum initial investment (by purchase, exchange or transfer)

•  Any individual retirement account of an Eligible Investor;

•  Any group retirement plan, not holding Fund shares in an omnibus manner, for which an intermediary or other entity provides services and is not compensated by the Fund for those services, other than compensation for shareholder servicing or sub-accounting performed in place of the transfer agent;

•  Any shareholder (as well as any family member of a shareholder or person listed on an account registration for any account of the shareholder) of a fund distributed by Columbia Management Distributors, Inc. (CMD) (i) who holds Class Z shares; (ii) who holds shares issued upon conversion of Primary A shares held prior to August 22, 2005; (iii) who holds Class A shares that were obtained by exchange of Class Z shares; or (iv) who holds no-load shares issued upon the merger of a fund distributed by CMD;

•  Any trustee or director (or family member of a trustee or director) of any fund distributed by CMD (other than the Columbia Acorn Funds);

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•  Any employee (or family member of an employee) of Bank of America Corporation or a subsidiary (other than Columbia Wanger Asset Management L.P.);

•  Any investor participating in an account offered by an intermediary or other entity that provides services to such an account, is paid an asset-based fee by the investor and is not compensated by the Funds for those services, other than payments for shareholder servicing or sub-accounting performed in place of the Fund's transfer agent (each investor purchasing through an intermediary must independently satisfy the $75,000 minimum investment requirement);

•  Any client of Bank of America Corporation or a subsidiary purchasing through an asset management company, trust, fiduciary, retirement plan administration or similar arrangement with Bank of America Corporation or the subsidiary;

•  Any person investing all or part of the proceeds of a distribution, rollover or transfer of assets into a Columbia Management Individual Retirement Account from any deferred compensation plan which was a shareholder of any of the funds of Columbia Acorn Trust (formerly named Liberty Acorn Trust) on September 29, 2000, in which the investor was a participant and through which the investor invested in one or more of the funds of Columbia Acorn Trust immediately prior to the distribution, transferor rollover;

•  Any investor purchasing through a Columbia Management state tuition plan organized under Section 529 of the Internal Revenue Code;

•  Any institutional investor which is a corporation, partnership, trust, foundation, endowment, institution, government entity, or similar organization; which meets the respective qualifications for an accredited investor, as defined under the Securities Act of 1933; or

•  Certain financial institutions and intermediaries, such as insurance companies, trust companies, banks, endowments, investment companies or foundations, purchasing shares for its own account, including Bank of America Corporation, its affiliates, or subsidiaries.

The investment minimum is applied at the class level. For group retirement plans, the investment minimum is determined based on the amount of the plan's investment rather than that of its individual participants. The Fund may establish exclusions from the investment minimum from time to time that it deems appropriate and consistent with the interests of shareholders. Please see the SAI for details on these exclusions.

The Fund reserves the right to change the criteria for eligible investors and the investment minimums. For accounts opened prior to December 15, 2003, no minimum investment applies to accounts participating in the automatic investment plan; however, each investment requires a $50 minimum purchase. The Fund also reserves the right to refuse a purchase order for any reason, including if it believes that doing so would be in the best interest of the Fund and its shareholders. Finally, pursuant to the Trust's Agreement and Declaration of Trust, the Fund reserves the right to redeem your shares if your account falls below the minimum investment requirements.

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SALES CHARGES (COMMISSIONS)

Your purchases of Class Z shares are at net asset value, which is the value of a Class Z share excluding any sales charge. Class Z shares are not subject to an initial sales charge when purchased, or a contingent deferred sales charge when sold.

CHOOSING A SHARE CLASS

The Fund offers one class of shares in this prospectus — Class Z.

The Fund also offers three additional classes of shares — Class A, B and C shares are available through a separate prospectus. Each other share class has its own sales charge and expense structure.

Broker-dealers, investment advisers or financial planners selling mutual fund shares may offer their clients more than one class of shares in a fund with different pricing options. This allows you and your financial advisor to choose among different types of sales charges and different levels of ongoing operating expenses, depending on the investment programs your financial advisor offers. Investors should consider carefully any separate transactions and other fees charged by these programs in connection with investing in any available share class before selecting a share class.

Determining which share class is best for you depends on the dollar amount you are investing and the number of years for which you are willing to invest. Based on your personal situation, your financial advisor can help you decide which class of shares makes the most sense for you. In general, anyone who is eligible to purchase Class Z shares, which do not incur Rule 12b-1 fees or sales charges, should do so in preference over other classes.

If you purchase Class Z shares of the Fund through certain intermediaries, they may charge a fee for their services. They may also place limits on your ability to use services the Fund offers. There are no sales charges or limitations if you purchase shares directly from the Fund, except as described in this prospectus.

If an intermediary is an agent or designee of the Fund, orders are processed at the net asset value next calculated after the intermediary receives the order. The intermediary must segregate any orders it receives after the close of regular trading on the NYSE and transmit those orders separately for execution at the net asset value next determined.

HOW TO EXCHANGE SHARES

You may exchange your shares for Class Z or Class A (only if Class Z is not offered) shares of another fund distributed by CMD at net asset value. Unless your account is part of a tax-deferred retirement plan, an exchange is a taxable event, and you may realize a gain or a loss for tax purposes. The Fund may terminate your exchange privilege if the adviser determines that your exchange activity is likely to adversely impact its ability to manage the Fund. See "Fund Policy on Trading of Fund Shares" for the Fund's policy. To exchange by telephone, call 1-800-422-3737. Please have your account and taxpayer identification numbers available when calling.

You also may exchange your shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet exchanges. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

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Your Account

HOW TO SELL SHARES

You may sell shares of the Fund on any regular business day that the NYSE is open.

When the Fund receives your sales request in "good form," shares will be sold at the next calculated net asset value. "Good form" means the Fund's transfer agent has all information and documentation it deems necessary to effect your order. For example, when selling shares by letter of instruction, "good form" means (i) your letter has complete instructions, the proper signatures and Medallion Signature Guarantees, and (ii) any other required documents are attached. For additional documents required for sales by corporations, agents, fiduciaries, surviving joint owners and other legal entities, please call 1-800-345-6611. Retirement plan accounts have special requirements; please call 1-800-799-7526 for more information.

The Fund will generally send proceeds from the sale to you within seven days (usually on the next business day after your request is received in "good form"). However, if you purchased your shares by check, the Fund may delay sending the proceeds from the sale of your shares for up to 10 days after your purchase to protect against checks that are returned. No interest will be paid on uncashed redemption checks. Redemption proceeds may be paid in securities, rather than cash, under certain circumstances. For more information, see the paragraph "Non-Cash Redemptions" under the section "How to Sell Shares" in the SAI.

During any 90-day period for any one shareholder, the Fund is obligated to redeem shares solely in cash up to the lesser of $250,000 or 1% of the Fund's net assets. Redemptions in excess of these limits will normally be paid in cash, but may be paid wholly or partly by an in-kind distribution of securities.

Outlined below are the various options for selling shares:

Method	Instructions
Through your financial advisor	You may call your financial advisor to place your sell order. To receive the current trading day's price, your financial advisor must receive your request prior to the close of regular trading on the NYSE, usually 4:00 p.m. Eastern time. Your financial advisor may charge you fees for executing a redemption for you.
By exchange	You or your financial advisor may sell Fund shares by exchanging from the Fund into Class Z shares or Class A shares (only if Class Z is not offered) of another fund distributed by Columbia Management Distributors, Inc. at no additional cost. To exchange by telephone, call 1-800-422-3737.
By telephone	You or your financial advisor may sell Fund shares by telephone and request that a check be sent to your address of record by calling 1-800-422-3737, unless you have notified the Fund of an address change within the previous 30 days. The dollar limit for telephone sales is $100,000 in a 30-day period. You do not need to set up this feature in advance of your call. Certain restrictions apply to retirement accounts. For details, call 1-800-799-7526.
By mail	You may send a signed letter of instruction to the address below. In your letter of instruction, note the Fund's name, share class, account number, and the dollar value or number of shares you wish to sell. All account owners must sign the letter. Signatures must be guaranteed by either a bank, a member firm of a national stock exchange or another eligible guarantor that participates in the Medallion Signature Guarantee Program for amounts over $100,000 or for alternate payee or mailing instructions. Additional documentation is required for sales by corporations, agents, fiduciaries, surviving joint owners and individual retirement account owners. For details, call 1-800-345-6611. Mail your letter of instruction to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By wire	You may sell Fund shares and request that the proceeds be wired to your bank. You must set up this feature prior to your request. Be sure to complete the appropriate section of the account application for this feature. Generally, the value of your redemption must be at least equal to $500 in order to have the sale proceeds wired to your bank. There is a $7.50 charge for wiring sale proceeds to your bank. (The transfer agent may waive this fee for omnibus and nominee accounts.) Your bank may charge additional fees for such wire transfer.
By systematic withdrawal plan	You may automatically sell a specified dollar amount or percentage of your account on a monthly, quarterly or semiannual basis and have the proceeds sent to you if your account balance is at least $5,000. The $5,000 minimum account balance is waived for wrap accounts. All dividend and capital gains distributions must be reinvested. Be sure to complete the appropriate section of the account application for this feature.

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Method	Instructions
By electronic funds transfer	You may sell Fund shares and request that the proceeds be electronically transferred to your bank. Proceeds may take up to two business days to be received by your bank. You must set up this feature prior to your request. Be sure to complete the appropriate section of the account application for this feature.
Through the internet	You may sell Fund shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet redemptions. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

FUND POLICY ON TRADING OF FUND SHARES

The interests of the Fund's long-term shareholders may be adversely affected by certain short-term trading activity by Fund shareholders. Such short-term trading activity, when excessive, has the potential to interfere with efficient portfolio management, generate transaction and other costs, dilute the value of Fund shares held by long-term shareholders and have other adverse effects on the Fund. This type of excessive short-term trading activity is referred to herein as "market timing." For purposes of this section, "Columbia Funds" are the Columbia, Columbia Acorn Trust and Wanger Advisors Trust families of mutual funds. The Columbia Funds are not intended as vehicles for market timing. The Board of Trustees of the Fund has adopted the policies and procedures set forth below with respect to frequent trading of the Fund's shares.

The Fund, directly and through its agents, takes various steps designed to deter and curtail market timing. For example, if the Fund detects that any shareholder has conducted two "round trips" (as defined below) in the Fund in any 28-day period, except as noted below with respect to orders received through omnibus accounts, the Fund will reject the shareholder's future purchase orders, including exchange purchase orders, involving any Columbia fund (other than a money market fund). In addition, if the Fund determines that any person, group or account has engaged in any type of market timing activity (independent of the two-round-trip limit), the Fund may, in its discretion, reject future purchase orders by the person, group or account, including exchange purchase orders, involving the same or any other Columbia fund, and also retains the right to modify these market timing policies at any time without prior notice.

The rights of shareholders to redeem shares of the Fund are not affected by any of the limits mentioned above. However, certain funds (other than the Fund) impose a redemption fee on the proceeds of fund shares that are redeemed or exchanged within 60 days of their purchase.

For these purposes, a "round trip" is a purchase by any means into a Columbia fund followed by a redemption, of any amount, by any means out of the same Columbia fund. Under this definition, an exchange into the Fund followed by an exchange out of the Fund is treated as a single round trip. Also for these purposes, where known, accounts under common ownership or control generally will be counted together. Accounts maintained or managed by a common intermediary, such as an adviser, selling agent or trust department, generally will not be considered to be under common ownership or control.

Purchases, redemptions and exchanges made through the Columbia Funds' Automatic Investment Plan, Systematic Withdrawal Plan or similar automated plans are not subject to the two-round-trip limit. Purchases, redemptions and exchanges made by Columbia Thermostat Fund are also not subject to the two round-trip limit. The two-round-trip limit may be modified for, or may not be applied to, accounts held by certain retirement plans to conform to plan limits, considerations relating to the Employee Retirement Income Security Act of 1974 or regulations of the Department of Labor, and for certain asset allocation or wrap programs.

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The practices and policies described above are intended to deter and curtail market timing in the Fund. However, there can be no assurance that these policies, individually or collectively, will be totally effective in this regard because of various factors. In particular, a substantial portion of purchase, redemption and exchange orders are received through omnibus accounts. Omnibus accounts, in which shares are held in the name of an intermediary on behalf of multiple beneficial owners, are a common form of holding shares among financial intermediaries and retirement plans. The Fund typically is not able to identify trading by a particular beneficial owner through an omnibus account, which may make it difficult or impossible to determine if a particular account is engaged in market timing. Consequently, there is the risk that the Fund may not be able to identify, deter or curtail certain market timing that occurs in the Fund, which may result in certain shareholders being able to market time the Fund while the shareholders in the Fund bear the burden of such activities.

Certain financial intermediaries, including certain retirement plan service providers whose clients include, among others, various retirement plans sponsored by Bank of America and its affiliates for the benefit of its employees (the "Bank of America retirement plan service providers"), have different policies regarding monitoring and restricting market timing in the underlying beneficial owner accounts that they maintain through an omnibus account that may be more or less restrictive than the Fund practices discussed above. In particular, the Bank of America retirement plan service providers permit the reinstatement of future purchase orders for shares of the Fund following various suspension periods. If an intermediary does not enforce the Fund's policy, the intermediary must either provide data transparency to Columbia Management or Columbia Management must determine that the intermediary's policy taken in its entirety provid es protections to Fund Shareholders that are generally commensurate with the Fund's policy.

The Fund seeks to act in a manner that it believes is consistent with the best interests of Fund shareholders in making any judgments regarding market timing. Neither the Fund nor its agents shall be held liable for any loss resulting from rejected purchase orders or exchanges.

FINANCIAL INTERMEDIARY PAYMENTS

The Fund's distributor, investment adviser or their affiliates may make payments, from their own resources, to certain financial intermediaries, including other Bank of America affiliates, for marketing support services. For purposes of this section the term "financial intermediary" includes any broker, dealer, bank, bank trust department, registered investment adviser, financial planner, retirement plan or other third-party administrator and any other institution having a selling, services or any similar agreement with the Fund's distributor, investment adviser or one of their affiliates. These payments are generally based upon one or more of the following factors: average net assets of the mutual funds distributed by the Fund's distributor attributable to that financial intermediary, gross sales of the mutual funds distributed by the Fund's distributor attributable to that financial intermediary, reimbursement of ticket charge s (fees that a financial intermediary firm charges its representatives for effecting transactions in fund shares) or a negotiated lump sum payment.

While the financial arrangements may vary for each financial intermediary, the payments to any one financial intermediary are generally expected to be between 0.05% and 0.45% on an annual basis for payments based on average net assets of the Fund attributable to the financial intermediary, and between 0.10% and 0.25% on an annual basis for firms receiving a payment based on gross sales of the Fund attributable to the financial intermediary. The Fund's distributor, investment adviser or their affiliates may make payments in materially larger amounts or on a basis materially different from those described above when dealing with other affiliates of Bank

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of America. Such increased payments to the other Bank of America affiliate may enable the other Bank of America affiliate to offset credits that it may provide to its customers in order to avoid having such customers pay fees to multiple Bank of America entities in connection with the customer's investment in the Fund.

Payments also may be made to certain financial intermediaries, including other Bank of America affiliates, that provide investor services to retirement plans and other investment programs to compensate financial intermediaries for services they provide to such programs, including, but not limited to, sub-accounting, sub-transfer agency, similar shareholder or participant recordkeeping, shareholder or participant reporting, or shareholder or participant transaction processing. These payments for investor servicing support vary by financial intermediary but generally are not expected, with certain limited exceptions, to exceed 0.45% of the total Fund assets for Class Z shares in the program on an annual basis.

The Trust's Board of Trustees has authorized the Fund to pay to any intermediary up to 0.05% of the average aggregate value of Fund shares in the intermediary's program on an annual basis for providing investor services. Charges of an intermediary in excess of that paid by the Fund will be borne by the Fund's distributor or its affiliates.

The Fund's distributor, investment adviser or their affiliates may make other payments or allow promotional incentives to financial intermediaries to the extent permitted by the rules of the Securities and Exchange Commission, the National Association of Securities Dealers and by other applicable laws and regulations.

Amounts paid by the Fund's distributor, investment adviser or their affiliates are paid out of the distributor's, investment adviser's or their affiliates' own resources and do not increase the amount paid by you or the Fund. You can find further details about the payments made by the Fund's distributor, investment adviser or their affiliates and the services provided by financial intermediaries as well as a list of the financial intermediaries to which the Fund's distributor, investment adviser or their affiliates have agreed to make marketing support payments in the Fund's SAI. Your financial intermediary may charge you fees or commissions in addition to those disclosed in this prospectus. You can ask your financial intermediary for information about any payments it receives from the Fund's distributor, investment adviser and their affiliates and any services your financial intermediary provides, as well as fees and/or commiss ions it charges. In addition, depending on the financial arrangement in place at any particular time, a financial intermediary and its financial consultants also may have a financial incentive for recommending a particular fund or share class over others. You should consult with your financial adviser and review carefully any disclosure by the financial intermediary as to compensation received by your financial adviser.

OTHER INFORMATION ABOUT YOUR ACCOUNT

How the Fund's Share Price is Determined The Fund's Class Z share price is based on its net asset value. The net asset value is determined at the close of regular trading on the NYSE, usually 4:00 p.m. Eastern time, on each business day that the NYSE is open for trading (typically Monday through Friday). Net asset value is not determined on days on which the NYSE is closed for trading.

When you request a transaction, it will be processed at the net asset value per share next determined after your request is received in "good form" by the distributor. In most cases, in order to receive that day's price, the Fund must receive your order before that day's transactions are processed. If you request a transaction through your financial advisor, your financial advisor must receive your order by the close of trading on the NYSE to receive that day's price.

14

Your Account

The Fund determines its net asset value for its Class Z shares by dividing total net assets attributable to Class Z shares by the number of outstanding Class Z shares. In determining the net asset value, the Fund must determine the value of each security in its portfolio at the close of each trading day. Because the Fund may hold securities that are traded on foreign exchanges, the value of the Fund's securities may change on days when shareholders will not be able to buy or sell Fund shares. This will affect the Fund's net asset value on the day it is next determined. Securities for which market quotations are available are valued each day at the current market value. However, where market quotations are unavailable, or when the adviser believes that subsequent events have made them unreliable, the Fund may use other data to determine the fair value of the securities.

The Fund has retained an independent statistical fair value pricing service to assist in the fair valuation process for securities principally traded in a foreign market in order to adjust for possible changes in value that may occur between the close of the foreign exchange and the time at which Fund shares are priced. The use of an independent fair value pricing service is intended to and may decrease the opportunities for time zone arbitrage transactions. There can be no assurance that the use of an independent fair value pricing service will successfully decrease arbitrage opportunities. If a security is valued at a "fair value," that value may be different from the last quoted market price for the security.

You can find the daily prices of some share classes for the Fund in most major daily newspapers under the heading of "Columbia." You can find daily prices for all share classes by visiting www.columbiafunds.com.

Share Certificates Share certificates are not available for Class Z shares.

Dividends, Distributions, and Taxes The Fund has the potential to make the following distributions:

Types of Distributions

Dividends	Represents interest and dividends earned from securities held by the Fund, net of expenses incurred by the Fund.
Capital gains	Represents net long-term capital gains on sales of securities held for more than one year and net short-term capital gains, which are gains on sales of securities held for a one-year period or less.

Distribution Options The Fund distributes any dividends in June and December and any capital gains (including short-term capital gains) at least annually. You can choose one of the options listed in the table below for these distributions when you open your account. To change your distribution option call 1-800-345-6611.

If you do not indicate on your application or at the time your account is established your preference for handling distributions, the Fund will automatically reinvest all distributions in additional shares of the Fund.

UNDERSTANDING FUND DISTRIBUTIONS

The Fund may earn income from the securities it holds. The Fund also may realize capital gains or losses on sales of its securities. The Fund intends to distribute substantially all of its net investment income and capital gains to shareholders each year. As a shareholder, you are entitled to a portion of the Fund's income and capital gains based on the number of shares you own at the time these distributions are declared.

15

Your Account

Distribution Options

Reinvest all distributions in additional shares of the Fund

Reinvest all distributions in shares of another fund

Receive dividends in cash (see options below) and reinvest capital gains

Receive all distributions in cash (with one of the following options):

•  send the check to your address of record

•  send the check to a third-party address

•  transfer the money to your bank via electronic funds transfer

Distributions of $10 or less will automatically be reinvested in additional Fund shares. If you elect to receive distributions by check and the check is returned as undeliverable, all subsequent distributions will be reinvested in additional shares of the Fund.

Taxes Unless you are an entity exempt from income taxes or invest under a retirement account, regardless of whether you receive your distributions in cash or reinvest them in additional Fund shares, all Fund distributions are subject to federal income tax. Depending on where you live, distributions also may be subject to state and local income taxes.

The Fund intends to elect to be treated and to qualify each year as a regulated investment company. A regulated investment company is not subject to tax at the corporate level on income and gains from investments that are distributed to shareholders in accordance with applicable law. However, the Fund's failure to qualify as a regulated investment company could result in corporate level taxation, and consequently, a reduction in income available for distribution to shareholders.

In general, any distributions of dividends, interest and short-term capital gains (determined by how long the Fund held the investments that generated them) are taxable as ordinary income, unless such dividends are "qualified dividend income" (as defined in the Internal Revenue Code) eligible for a reduced rate of tax. Properly designated distributions of long-term capital gains (determined by how long the Fund held the investments that generated them) are generally taxable as such, regardless of how long you have held your Fund shares. You will be provided with information each year regarding the amount of ordinary income and capital gains distributed to you for the previous year and any portion of your distribution which is exempt from state and local taxes. Long-term capital gain rates have been reduced – in general, to 15% with lower rates applying to taxpayers in the 10% and 15% rate brackets – for taxable years b eginning before January 1, 2011. Distributions are taxable to you even if they are paid from income or gains earned by the Fund before you made your investment (and thus were included in the price you paid). Your investment in the Fund may have additional personal tax implications. Please consult your tax advisor about foreign, federal, state, local or other applicable tax laws.

In addition to the dividends and capital gains distributions made by the Fund, you may realize a capital gain or loss when selling or exchanging shares of the Fund. Such transactions also may be subject to federal, state and local income taxes.

Foreign Income Taxes The Fund may receive investment income from sources within foreign countries, and that income may be subject to foreign income taxes at the source. If the Fund pays non-refundable taxes to foreign governments during the year, the taxes will reduce the Fund's dividends but will still be included in your taxable income.

16

Board of Trustees

The Fund is governed by its Board of Trustees. More than 75% of the Fund's Trustees are independent, meaning that they have no affiliation with the adviser or the Funds, apart from their positions as Trustees and the personal investments they may have made as private individuals.

The independent Trustees bring backgrounds in business and the professions and academia service to their task of working with the Funds' officers to establish the policies and oversee the activities of the Funds. Among the Trustees' responsibilities are selecting the investment adviser for the Funds; negotiating the advisory agreements; reviewing other contracts; approving investment policies; monitoring Fund operations, performance, and costs; and nominating or selecting new Trustees.

Each Trustee serves until his or her retirement, resignation, death or removal; or otherwise as specified in the Trust's organizational documents. It is expected that every five years the Trustees will call a meeting of shareholders to elect Trustees. A Trustee must retire at the end of the year in which he or she attains the age of 75. Any Trustee may be removed at a shareholders' meeting by a vote representing two-thirds of the net asset value of all shares of the Funds of the Trust. The mailing address for the Trustees and officers is 227 W. Monroe, Suite 3000, Chicago, Illinois 60606.

For more detailed information on the Board of Trustees, please refer to the SAI.

Managing the Fund

INVESTMENT ADVISER

Columbia Wanger Asset Management, L.P. (CWAM), located at 227 West Monroe Street, Suite 3000, Chicago, Illinois 60606, is the Fund's investment adviser and is responsible for the Fund's management, subject to the oversight of the Fund's Board of Trustees. CWAM and its predecessor have managed mutual funds, including the Fund, since 1992. In its duties as investment adviser, CWAM runs the Fund's day-to-day business, including making investment decisions and placing all orders for the purchase and sale of the Fund's portfolio securities.

CWAM was previously named Liberty Wanger Asset Management, L.P., and its predecessor was named Wanger Asset Management, L.P. (WAM). CWAM is a wholly owned subsidiary of Columbia Management Group, LLC, which in turn is an indirect wholly owned subsidiary of Bank of America Corporation. As of December 31, 2006, CWAM managed more than $32.9 billion in assets.

CWAM's advisory fee for managing the Fund in 2006 was 0.64% of the Fund's average daily net assets. CWAM also received an administrative fee from the Fund in 2006 of 0.04% of the Fund's average daily net assets. A discussion of the factors considered by the Fund's Board of Trustees in approving the Fund's investment advisory contract is included in the Fund's annual report to shareholders for the period ended December 31, 2006.

PORTFOLIO MANAGERS

CWAM uses a team to assist the portfolio managers in managing the Fund. Team members share responsibility for providing ideas, information and knowledge in managing the Fund, and each team member has one or more particular areas of expertise. Portfolio managers make strategic decisions and monitor and supervise individual transactions. While certain analysts recommend transactions for approval by the portfolio managers, more seasoned analysts are authorized to buy and sell securities for the Fund within the guidelines set by portfolio managers.

17

Managing the Fund

Charles P. McQuaidLead portfolio manager
Charles McQuaid is president of the Trust and a member of the Trust's Board of Trustees. He has been president of CWAM since October 2003, chief investment officer of CWAM since October 2003, and was director of research at CWAM and its predecessor from July 1992 through December 2003. Mr. McQuaid has been a member of Columbia Acorn Fund's management team since 1978, co-managed Columbia Acorn Fund from 1995 through September 2003 and has been the Fund's lead portfolio manager since September 2003. He served as CWAM's interim director of international research from October 2003 to December 2004. Mr. McQuaid has been president of Wanger Advisors Trust since 2003 and a trustee since September 2006. He also manages two domestic separate accounts and two offshore funds.

Robert A. Mohn
Co-portfolio manager
Robert Mohn is a vice president of the Trust. He has been a member of the domestic analytical team at CWAM and its predecessor since August 1992. He has managed Columbia Acorn USA since its inception in 1996, co-managed Columbia Acorn Fund since May 2003, and also manages Wanger U.S. Smaller Companies, a mutual fund underlying variable insurance products, and the U.S. fund of an investment company whose shares are offered only to non-U.S. investors. Mr. Mohn also is a vice president of Wanger Advisors Trust and the director of domestic research for CWAM.

The SAI provides additional information about the portfolio managers' compensation, other accounts managed and ownership of securities in the Fund.

LEGAL PROCEEDINGS

The Trust, CWAM and the trustees of the Trust (collectively, the "Columbia defendants") are named as defendants in class and derivative complaints, which were consolidated in a Multi-District Action in the federal district court for the District of Maryland on February 20, 2004 (the "MDL Action"). These lawsuits contend that defendants permitted certain investors to market time their trades in certain Columbia Acorn Funds. The MDL Action is ongoing. All claims against the Trust and its independent trustees have been dismissed; however, the interested trustees of the Trust are still parties to the MDL Action.

On March 21, 2005, a class action complaint was filed against the Trust in the Superior Court of the Commonwealth of Massachusetts seeking to rescind the contingent deferred sales charges assessed upon redemption of Class B shares of Columbia Acorn Funds due to the alleged market timing by certain shareholders of the Columbia Acorn Funds. In addition to the rescission of sales charges, plaintiffs seek recovery of actual damages, attorneys' fees and costs. The case has been transferred to the MDL Action in the federal district court of Maryland.

The Trust and CWAM are also defendants in a class action lawsuit, filed on November 13, 2003 in the Circuit Court of the Third Judicial Circuit, Madison County, Illinois, that alleges, in summary, that the Trust and CWAM exposed shareholders of Columbia Acorn International to trading by market timers by allegedly (a) failing to properly evaluate daily whether a significant event affecting the value of that fund's securities had occurred after foreign markets had closed but before the calculation of the fund's net asset value; (b) failing to implement the fund's portfolio valuation and share pricing policies and procedures; and (c) failing to know and implement applicable rules and regulations concerning the calculation of net asset value ("Fair Valuation Lawsuit"). On April 5, 2005, the United States Court of Appeals for the Seventh Circuit ruled that the plaintiffs' state law claims were preempted under federal law resulting in the dismissal of plaintiffs' complaint. Plaintiffs appealed the

18

Managing the Fund

Seventh Circuit's ruling to the United States Supreme Court. On June 15, 2006, the Supreme Court reversed the Seventh Circuit's ruling on jurisdictional grounds, and the case ultimately was remanded to the state court.

On April 4, 2006, the plaintiffs and the Columbia defendants named in the MDL Action executed an agreement in principle intended to fully resolve all of the lawsuits consolidated in the MDL Action as well as the Fair Valuation Lawsuit. The court entered a stay after the parties executed the agreement in principle. The settlement is subject to court approval.

In 2004, CWAM and the trustees of the Columbia Acorn Trust were named as defendants in certain purported shareholder class and derivative actions making claims, including claims under the Investment Company and the Investment Advisers Acts of 1940 and state law. Certain Columbia Acorn Funds were named as nominal defendants. The suits allege, inter alia, that the fees and expenses paid by the funds are excessive and that the funds' advisers and their affiliates inappropriately used fund assets to distribute the funds and for other improper purposes. On March 2, 2005, the actions were consolidated in the Massachusetts federal court as In re Columbia Entities Litigation. The plaintiffs filed a consolidated amended complaint on June 9, 2005. On November 30, 2005, the judge dismissed all claims by plaintiffs and entered final judgment in favor of the defendants. The plaintiffs appealed to the United States Court of Appeals for the First Circuit on December 30, 2005. A stipulation and settlement agreement dated January 19, 2007 was filed in the First Circuit on February 14, 2007, with a joint stipulation of dismissal and motion for remand to obtain district court approval of the settlement. The joint motion was granted and the appeal was dismissed. On March 6, 2007, the case was remanded to the District Court, where the parties will seek court approval of the settlement. The terms of the proposed settlement, if approved, will require payments by the funds' adviser and/or its affiliates, including payment of plaintiffs' attorneys' fees and notice to class members. In the event that the settlement is not approved, the plaintiffs may elect to g o forward with their appeal and no opinion is expressed regarding the likely outcome or financial impact of such an appeal on any fund.

On or about January 11, 2005, a putative class action lawsuit was filed in federal district court in Massachusetts against the Trust and its trustees, along with Columbia Management Advisors, LLC, the sub-administrator of the Wanger Advisors Funds and the Columbia Acorn Funds. The plaintiffs allege that the defendants failed to submit Proof of Claims in connection with settlements of securities class action lawsuits filed against companies in which the Columbia Acorn Funds held positions. The complaint seeks compensatory and punitive damages, and the disgorgement of all fees paid to Columbia Management Advisors, LLC. Plaintiffs have voluntarily dismissed the Trust and its independent trustees.

The Trust and CWAM intend to defend these suits vigorously.

As a result of these matters or any adverse publicity or other developments resulting from them, there may be increased redemptions or reduced sales of Fund shares, which could increase transaction costs or operating expenses, or have other adverse consequences for the Fund.

However, based on currently available information, the Trust believes that the likelihood that these lawsuits will have a material adverse impact on any fund is remote, and CWAM believes that the lawsuits are not likely to materially affect its ability to provide investment management services to the Fund.

19

Other Investment Strategies and Risks

The Fund's principal investment strategies and associated risks are described under "The Fund — Principal Investment Strategies" and "The Fund — Principal Investment Risks." This section describes other investments the Fund may make and the risks associated with them. In seeking to achieve its investment goal, the Fund may invest in various types of securities and engage in various investment techniques, which are not the principal focus of the Fund and therefore are not described in this prospectus. These types of securities and investment practices and their associated risks are identified and discussed in the Fund's SAI, which you may obtain free of charge (see back cover). The adviser may elect not to buy any of these securities or use any of these techniques. The Fund may not always achieve its investment goal. Except as otherwise noted, approval by the Fund's shareholders is not required to modify or change the F und's investment strategies.

THE INFORMATION EDGE

The Fund generally invests in entrepreneurially managed smaller- and mid-sized companies that it believes are not as well known by financial analysts and whose position in a niche creates the opportunity for superior earnings growth potential. CWAM may identify what it believes are important economic, social or technological trends (for example, the growth of outsourcing as a business strategy, or the productivity gains from the increasing use of technology) and try to identify companies it thinks will benefit from those trends.

In making investments for the Fund, CWAM relies primarily on independent, internally generated research to uncover companies that may be less well known than the more popular names. To find these companies, CWAM compares growth potential, financial strength and fundamental value among companies.

Growth Potential	Financial Strength	Fundamental Value
• superior technology • innovative marketing • managerial skill • market niche • good earnings prospects • strong demand for product	• low debt • adequate working capital • conservative accounting practices • adequate profit margin	• reasonable stock price relative to growth potential and financial strength • valuable assets
The realization of this growth potential would likely produce superior performance that is sustainable over time.	A strong balance sheet gives management greater flexibility to pursue strategic objectives and is important to maintaining a competitive advantage.	Once CWAM uncovers an attractive company, it identifies a price that it believes would also make the stock a good value.

LONG-TERM INVESTING

CWAM's analysts continually screen companies and make contact with more than 1,000 companies around the globe each year. To accomplish this, CWAM analysts often talk directly to top management, vendors, suppliers and competitors.

In managing the Fund, CWAM tries to maintain lower taxes and transaction costs by investing with a long-term time horizon (at least two to five years). However, securities purchased on a long-term basis may be sold within 12 months after purchase due to changes in the circumstances of a particular company or industry, or changes in general market or economic conditions.

20

Other Investment Strategies and Risks

DERIVATIVE STRATEGIES

The Fund may enter into a number of derivative strategies, including those that employ futures, options, straddles or similar transactions, to gain or reduce exposure to particular securities or markets. These strategies, commonly referred to as derivatives, involve the use of financial instruments whose values depend on, or are derived from, the value of an underlying security, index or currency. The Fund may use these strategies to adjust the Fund's sensitivity to changes in interest rates, or for other hedging purposes (i.e., attempting to offset a potential loss in one position by establishing an interest in an opposite position). Derivative strategies involve the risk that they may exaggerate a loss, potentially losing more money than the actual cost of the underlying security, or limit a potential gain. Also, with some derivative strategies there is a risk that the other party to the transaction may fail to honor its contr act terms, causing a loss to the Fund or that the Fund may not be able to find a suitable derivative transaction counterparty, and thus may be unable to invest in derivatives altogether.

TEMPORARY DEFENSIVE STRATEGIES

At times, CWAM may determine that adverse market conditions make it desirable to temporarily suspend the Fund's normal investment activities. During such times, the Fund may, but is not required to, invest in cash or high-quality, short-term debt securities, without limit. Taking a temporary defensive position may prevent the Fund from achieving its investment goal.

21

Financial Highlights

The financial highlights table is intended to help you understand the Fund's Class Z financial performance. Information is shown for the Fund's last five fiscal years, which run from January 1 to December 31. Certain information in the table reflects the financial results for a single Class Z share. The total returns in the table represent the return that you would have earned (or lost) on an investment in the Fund (assuming reinvestment of all dividends and distributions). This information has been derived from the Fund's financial statements, which have been audited for the years ended December 31, 2004, 2005 and 2006 by PricewaterhouseCoopers LLP, an independent registered public accounting firm, whose report, along with the Fund's financial statements, is included in the Fund's annual report. The information for the years ended December 31, 2002 and 2003 is included in the Fund's financial statements that have been audited b y another independent registered public accounting firm, whose report expressed an unqualified opinion on those financial statements and highlights. You can request a free annual report containing those financial statements by calling 1-800-345-6611.

Columbia Acorn Fund

	Year ended December 31,
	2006			2005			2004			2003			2002
	Class Z			Class Z			Class Z			Class Z			Class Z
Net asset value — Beginning of period ($)		28.17			26.45			22.56			15.50			17.88
Income from Investment Operations ($):
Net investment income(a)		0.13			0.15			0.04			0.03			0.02
Net realized and unrealized gain (loss)		3.92			3.28			4.78			7.05			(2.40	)
Total from Investment Operations		4.05			3.43			4.82			7.08			(2.38	)
Less Distributions Declared to Shareholders ($):
From net investment income		(0.13	)		(0.15	)		(0.02	)		—			—
From net realized gains (losses)		(2.38	)		(1.56	)		(0.91	)		(0.02	)		—
Total Distributions Declared to Shareholders		(2.51	)		(1.71	)		(0.93	)		(0.02	)		—
Net asset value — End of period ($)		29.71			28.17			26.45			22.56			15.50
Total return (%)(b)		14.45	(c)		13.11	(c)		21.51	(c)		45.68			(13.31	)
Ratios to Average Net Assets/Supplemental Data (%):
Expenses(d)		0.74			0.74			0.81			0.80			0.82
Net investment income(d)		0.45			0.57			0.18			0.17			0.15
Waiver/reimbursement		0.01			0.02			0.02			—			—
Portfolio turnover rate (%)		22			16			20			10			13
Net assets at end of period (in millions) ($)		12,128			10,399			8,689			7,065			4,022

(a)  Per share data was calculated using average shares outstanding during the period.

(b)  Total return at net asset value assuming all distributions reinvested.

(c)  Had the investment adviser and/or transfer agent not waived and/or reimbursed a portion of expenses, total return would have been reduced.

(d)  The benefits derived from custody fees paid indirectly had no impact.

22

Appendix

Hypothetical Investment and Expense Information

The Fund is required to disclose the following supplemental hypothetical investment information, which provides additional information about the effect of the expenses paid by the Fund, including investment advisory fees and other Fund costs, on the Fund's returns over a 10-year period. The table shows the estimated expenses that would be charged on a hypothetical investment of $10,000 in Class Z shares of the Fund assuming a 5% return each year, the cumulative return after fees and expenses, and the hypothetical year-end balance after fees and expenses. The table also assumes that all dividends and distributions are reinvested. The annual expense ratio used for the Fund, which is the same as that stated in the Annual Fund Operating Expenses table, is presented in the table, and is net of any contractual fee waivers or expense reimbursements for the period of the contractual commitment. Your actual costs may be higher or lower. As noted previously, the Fund's minimum investment for initial purchases or exchanges is $75,000.

Columbia Acorn Fund — Class Z Shares

Maximum Sales Charge 0.00%					Initial Hypothetical Investment Amount $10,000.00						Assumed Rate of Return 5%
Year		Cumulative Return Before Fees & Expenses			Annual Expense Ratio			Cumulative Return After Fees & Expenses			Hypothetical Year-End Balance After Fees & Expenses		Annual Fees & Expenses(1)
	1		5.00	%		0.75	%		4.25	%	$	10,425.00	$	76.59
	2		10.25	%		0.75	%		8.68	%	$	10,868.06	$	79.85
	3		15.76	%		0.75	%		13.30	%	$	11,329.96	$	83.24
	4		21.55	%		0.75	%		18.11	%	$	11,811.48	$	86.78
	5		27.63	%		0.75	%		23.13	%	$	12,313.47	$	90.47
	6		34.01	%		0.75	%		28.37	%	$	12,836.79	$	94.31
	7		40.71	%		0.75	%		33.82	%	$	13,382.35	$	98.32
	8		47.75	%		0.75	%		39.51	%	$	13,951.10	$	102.50
	9		55.13	%		0.75	%		45.44	%	$	14,544.02	$	106.86
	10		62.89	%		0.75	%		51.62	%	$	15,162.14	$	111.40
Total Gain After Fees and Expenses											$	5,162.14
Total Annual Fees and Expenses													$	930.32

(1)  Annual Fees and Expenses are calculated based on the average between the beginning and ending balance for each year. All information is calculated on an annual compounding basis.

23

FOR MORE INFORMATION

Additional information about the Fund's investments is available in the Fund's semiannual and annual reports to shareholders. The annual report contains a discussion of the market conditions and investment strategies that significantly affected the Fund's performance during its last fiscal year.

You may wish to read the SAI for more information on the Fund and the securities in which it invests. The SAI is incorporated into this prospectus by reference, which means that it is considered to be part of this prospectus.

You can get free copies of annual and semiannual reports and the SAI, request other information and discuss your questions about the Fund by visiting www.columbiafunds.com or by writing or calling the Fund's transfer agent at:

Columbia Management Services, Inc.
P.O. Box 8081
Boston, MA 02266-8081
1-800-345-6611

Text-only versions of all Fund documents can be viewed online or downloaded from the EDGAR database on the Securities and Exchange Commission internet site at www.sec.gov.

You can review and copy information about the Fund, including the SAI, by visiting the following location, and you can obtain copies upon payment of a duplicating fee, by electronic request at the e-mail address publicinfo@sec.gov or by writing the:

Public Reference Room
Securities and Exchange Commission
Washington, DC 20549-0102

Information on the operation of the Public Reference Room may be obtained by calling 1-202-942-8090.

Investment Company Act file number:
Columbia Acorn Trust: 811-01829
•  Columbia Acorn Fund

©2007 Columbia Management Distributors, Inc.
One Financial Center, Boston, MA 02111-2621
800.426.3750 www.columbiafunds.com

INT-36/130117-0507

Columbia^SM

Acorn International^®  Prospectus, May 1, 2007

Class A, B and C Shares

Advised by Columbia Wanger Asset Management, L.P.

TABLE OF CONTENTS

THE FUND	2
Investment Goal	2
Principal Investment Strategies	2
Principal Investment Risks	2
Portfolio Holdings Disclosure	4
Performance History	4
Commissions and Other Expenses	6
YOUR ACCOUNT	8
Choosing a Share Class	8
How to Buy Shares	9
Investment Minimums	9
Sales Charges (Commissions)	10
How to Exchange Shares	15
How to Sell Shares	16
Fund Policy on Trading of Fund Shares	17
Other Information About Your Account	20
BOARD OF TRUSTEES	22
MANAGING THE FUND	23
Investment Adviser	23
Portfolio Managers	23
Legal Proceedings	24
OTHER INVESTMENT STRATEGIES AND RISKS	25
The Information Edge	25
Long-Term Investing	26
Derivative Strategies	26
Temporary Defensive Strategies	27
FINANCIAL HIGHLIGHTS	28
APPENDIX	31

Although these securities have been registered with the Securities and Exchange Commission, the Commission has not approved or disapproved any shares offered in this prospectus or determined whether this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Acorn International^® is a trademark owned and registered by Columbia Acorn Trust, Columbia, Columbia Management^® and Columbia Management Services, Inc. are service marks owned and/or registered by Bank of America

The Fund

INVESTMENT GOAL

Columbia Acorn International (Acorn International^®) seeks to provide long-term growth of capital.

PRINCIPAL INVESTMENT STRATEGIES

Acorn International invests generally in stocks of non-U.S. small- and medium-sized companies. The Fund generally invests in the stocks of companies based outside the United States with capitalizations of less than $5 billion at the time of initial purchase. As long as a stock continues to meet the Fund's other investment criteria, the Fund may choose to hold a stock even if the issuing company's capitalization grows beyond a $5 billion capitalization.

Acorn International believes that smaller companies, particularly outside the United States, that are not as well known by financial analysts, may offer higher return potential than the stocks of larger companies.

Acorn International typically looks for companies with:

•  A strong business franchise that offers growth potential.

•  Products and services that give the company a competitive advantage.

•  A stock price the Fund's investment adviser believes is reasonable relative to the assets and earning power of the company.

Acorn International is an international fund and invests the majority (under normal market conditions, at least 75%) of its total assets in the stocks of foreign companies based in developed markets (for example, Japan, Canada and the United Kingdom) and emerging markets (for example, Mexico, Brazil and Korea).

Additional strategies that are not principal investment strategies and the risks associated with them are described later in this prospectus under "Other Investment Strategies and Risks."

PRINCIPAL INVESTMENT RISKS

The principal risks of investing in the Fund are described below. There are many circumstances (including additional risks that are not described here) which could prevent the Fund from achieving its investment goal. You may lose money by investing in the Fund.

Management risk means that the adviser's investment decisions might produce losses or cause the Fund to underperform when compared to other funds with a similar investment goal. Market risk means that security prices in a market, sector or industry may fall, reducing the value of your investment. Because of management and market risk, there is no guarantee that the Fund will achieve its investment goal or perform favorably among comparable funds.

Since the Fund purchases equity securities, it is subject to equity risk. This is the risk that stock prices will fall over short or extended periods of time. Although the stock market historically has outperformed other asset classes over the long term, the stock market tends to move in cycles. Individual stock prices may fluctuate drastically from day-to-day and may underperform other asset classes over an extended period of time. Individual companies may report poor results or be negatively affected by industry and/or economic trends and developments. The prices of securities issued by such companies may suffer a decline in response. These price movements may result from factors affecting individual companies, industries or the securities market as a whole.

2

The Fund

Because the Fund invests in stocks, the price of its shares – its net asset value (NAV) per share – fluctuates daily in response to changes in the market value of stocks.

Sector risk is inherent in the Fund's investment strategy. Companies that are in different but closely related industries are sometimes described as being in the same broad economic sector. The values of stocks of different companies in a market sector may be similarly affected by particular economic or market events. Although the Fund does not intend to focus on any particular sector, at times the Fund may have a large portion of its assets invested in a particular sector.

Foreign securities are subject to special risks. Foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the dollar value of foreign securities denominated in foreign currencies and U.S. dollars, without a change in the intrinsic value of those securities. The liquidity of foreign securities may be more limited than that of domestic securities, which means that the Fund may, at times, be unable to sell foreign securities at desirable prices. Brokerage commissions, custodial fees and other fees are generally higher for foreign investments. In addition, foreign governments may impose withholding taxes that would reduce the amount of income and capital gains available to distribute to shareholders. Other risks include possible delays in the settlement of transactions or in the notification of income; less publicly av ailable information about companies; the impact of political, social or diplomatic events; possible seizure, expropriation or nationalization of the company or its assets; and possible imposition of currency exchange controls.

Market timers. Because the Fund invests predominantly in foreign securities, the Fund may be particularly susceptible to market timers. Market timers generally attempt to take advantage of the way the Fund prices its shares by trading based on market information they expect will lead to a change in the Fund's net asset value on the next pricing day. Market timing activity may be disruptive to Fund management and, since a market timer's profits are effectively paid directly out of the Fund's assets, may negatively impact the investment returns of other shareholders. Although the Fund has adopted certain policies and methods intended to identify and to discourage frequent trading based on this strategy, it cannot ensure that all such activity can be identified or terminated.

Investments in emerging markets are subject to additional risk. The risks of foreign investments are typically increased in less developed countries, which are sometimes referred to as emerging markets. For example, political and economic structures in these countries may be new and developing rapidly, which may cause instability. These countries are also more likely to experience high levels of inflation, deflation or currency devaluations, which could hurt their economies and securities markets.

Small- or mid-cap companies may be more susceptible to market downturns, and their prices could be more volatile than large-cap companies. These companies are more likely than larger companies to have limited product lines, operating histories, markets or financial resources. They may depend heavily on a small management team and may trade less frequently, may trade in smaller volumes and may fluctuate more sharply in price than stocks of larger companies. In addition, such companies may not be widely followed by the investment community, which can lower the demand for their stocks.

An investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

3

The Fund

PORTFOLIO HOLDINGS DISCLOSURE

A description of the Fund's policies and procedures with respect to the disclosure of its portfolio securities is available in the Fund's Statement of Additional Information (SAI), which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611.

The Fund posts its complete portfolio holdings at as of month-end www.columbiafunds.com approximately 30-40 calendar days after such month-end. Additionally, the Fund discloses its top 15 month-end portfolio holdings at www.columbiafunds.com on or about 15 calendar days following such month-end.

Once posted, the above information will remain available on the website until at least the date on which the Fund files a Form N-CSR or Form N-Q for the period that includes the date as of which the information is current.

PERFORMANCE HISTORY

The bar chart below shows the Fund's calendar-year total returns (before taxes) for its Class A shares, excluding sales charges. The performance table following the bar chart shows how the Fund's average annual total returns for Class A, B and C shares, including sales charges, compare broad measures of market performance for one year, five years and the life of the share class. The chart and table are intended to illustrate some of the risks of investing in the Fund by showing the changes in the Fund's performance from year to year. All returns include the reinvestment of dividends and distributions. As with all mutual funds, past performance (before and after taxes) does not predict the Fund's future performance.

UNDERSTANDING PERFORMANCE

Calendar Year Total Returns show the Fund's Class A share performance for each completed calendar year since the Class commenced operations. Those returns include the effects of Fund expenses, but not the effects of sales charges paid directly by the shareholder. If sales charges were included, these returns would be lower.

Average Annual Total Returns are a measure of the Fund's average performance over the past one year, five years and the life of the share class. The table shows returns of each share class and includes the effects of both Fund expenses and current sales charges. Class B share returns do not reflect Class A share returns after conversion of Class B shares to Class A shares — see the section "Your Account — Sales Charges (Commissions)."

The Fund's returns are compared to the S&P/Citigroup EMI Global ex-U.S. index, the Morgan Stanley Europe, Australasia and Far East Index (EAFE) and the S&P/Citigroup Global ex-U.S. Cap Range $500M - $5B. The S&P/Citigroup EMI Global ex-U.S., the Fund's primary benchmark, is an index of the bottom 20% of institutionally investable capital of developed and emerging countries (after 9/30/1994), selected by the index sponsor, outside the United States. The Morgan Stanley Capital International (MSCI) Europe, Australasia, Far East (EAFE) Index is a free float-adjusted market capitalization index that is designed to measure developed market equity performance, excluding the U.S. and Canada. The S&P/Citigroup Global ex-U.S. Cap Range $500M - $5B is a subset of the broad market selected by the index sponsor representing the small- and mid-cap developed and emerging markets, excluding the United States. Unlike the Fund, in dices are not investments, do not incur fees, expenses or taxes, and are not professionally managed.

4

The Fund

Calendar Year Total Returns (Class A)

For the periods shown in bar chart:
Best quarter: 2nd quarter 2003, +21.37%
Worst quarter: 3rd quarter 2002, -19.96%

After-tax returns are calculated using the highest historical individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on each investor's own tax situation and may differ from those shown. After-tax returns may not be relevant to investors who hold Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Average Annual Total Returns — for periods ended December 31, 2006⁽¹⁾

Share Class	1 Year		5 Years		Life of the Share Class(2)
Class A (%)
Return Before Taxes		26.44		19.43		10.04
Return After Taxes on Distributions		24.33		18.91		9.14
Return After Taxes on Distributions and Sale of Fund Shares		19.36		17.20		8.48
Class B (%)
Return Before Taxes		28.26		19.82		10.35
Return After Taxes on Distributions		26.27		19.43		9.54
Return After Taxes on Distributions and Sale of Fund Shares		20.72		17.63		8.82
Class C (%)
Return Before Taxes		32.14		19.99		10.32
Return After Taxes on Distributions		30.19		19.60		9.52
Return After Taxes on Distributions and Sale of Fund Shares		23.24		17.79		8.80
Indices
S&P/Citigroup EMI Global ex-U.S. (%)		30.83		24.39		16.05	(3)
MSCI EAFE (%)		26.34		14.98		7.80	(3)
S&P/Citigroup Global ex-U.S. Cap Range $500M - $5B (%)		26.70		24.15		16.64	(4)

(1)  Performance may reflect any voluntary waiver or reimbursement of Fund expenses by the investment adviser or its affiliates. Absent these waivers or reimbursement arrangements, performance results would have been lower.

(2)  The inception date for Class A, Class B and Class C shares is October 16, 2000.

(3)  Performance information is from October 16, 2000.

(4)  Performance information is from October 31, 2000.

5

The Fund

COMMISSIONS AND OTHER EXPENSES

Expenses are one of several factors to consider before you invest in a mutual fund. The tables below describe the commissions and other expenses you may pay when you buy, hold and sell shares of the Fund.

UNDERSTANDING EXPENSES

Sales Charges (Commissions) are paid directly by shareholders to Columbia Management Distributors, Inc., the Fund's distributor, who compensates your financial advisor.

Annual Fund Operating Expenses are paid by the Fund. They include management and administration fees, 12b-1 fees and other expenses that generally include, but are not limited to, transfer agency, custody, and legal fees as well as costs related to state registration and printing of Fund documents. The specific fees and expenses that make up the Fund's other expenses will vary from time to time and may include fees or expenses not described here. The Fund will likely incur portfolio transaction costs that are in addition to the total annual fund operating expenses disclosed in the fee table. These transaction costs are made up of all costs that are associated with trading securities for the Fund's portfolio and include, but are not limited to, brokerage commissions and market spreads, as well as potential changes to the price of a security due to the Fund's efforts to purchase or sell it. While certain elements of transaction costs are readily identifiable and quantifiable, other elements that can make up a significant amount of the Fund's transaction costs are not. Higher transaction costs reduce the Fund's returns.

Shareholder Fees (commissions paid directly from your investment)

	Class A			Class B		Class C
Maximum sales charge (load) on purchases (%) (as a percentage of the offering price)		5.75		None		None
Maximum deferred sales charge (load) on redemptions (%) (as a percentage of the lesser of purchase price or redemption price)		1.00	(1)		5.00		1.00
Redemption fee (%) (as a percentage of amount redeemed, if applicable)	None(2)(3)			None(2)(3)		None(2)(3)

(1)  This charge applies only to certain purchases of Class A shares bought without an initial sales charge that are sold within 12 months of purchase.

(2)  There is a $7.50 charge for wiring sale proceeds to your bank.

(3)  A redemption fee of 2.00% may be charged on shares that were owned for 60 days or less. For more information, see "Fund Policy on Trading of Fund Shares" below.

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The Fund

Annual Fund Operating Expenses (deducted directly from Fund assets)

	Class A		Class B		Class C
Management fees(1) (%)		0.77		0.77		0.77
Distribution and service (12b-1) fees(2) (%)		0.25		0.75		1.00
Other expenses(3) (%)		0.25		0.34		0.28
Total annual fund operating expenses (%)		1.27		1.86		2.05

(1)  The Fund pays an investment advisory fee of 0.77%. The Fund and its adviser have implemented a breakpoint schedule for the Fund's investment advisory fees. The investment advisory fee rates charged to the Fund will decline as Fund assets grow and will continue to be based on a percentage of the Fund's average daily assets. The annual fee schedule for the Fund is as follows: 1.19% for assets up to $100 million; 0.94% for assets in excess of $100 million and up to $500 million; 0.74% for assets in excess of $500 million. In addition to the management fee, the Fund and the other funds of Columbia Acorn Trust (the "Trust") pay the adviser an administrative fee based on the average daily aggregate net assets of the Trust at the following annual rates: 0.05% of net assets up to $8 billion; 0.04% of the next $8 billion; and 0.03% of net assets in excess of $16 billion. Based on the Trust's average daily net assets as of December 31, 2006, the administrative fee would be at a rate of 0.04% and is included in "Other expenses."

(2)  The distribution and service (12b-1) fees for Class B shares have been restated to reflect a reduction of the distribution fee rate by 0.10%, effective August 1, 2006.

(3)  "Other expenses" have been restated to reflect contractual changes to the transfer agency fees paid by the Fund.

Example Expenses help you compare the cost of investing in the Fund to the cost of investing in other mutual funds. Ituses the following hypothetical conditions:

•  $10,000 initial investment

•  5% total return for each year

•  Fund operating expenses remain the same

•  Reinvestment of all dividends and distributions

•  Class B shares convert to Class A shares after eight years

Example Expenses for a $10,000 investment (your actual costs may be higher or lower)

Class	1 Year		3 Years		5 Years		10 Years
Class A	$	697	$	955	$	1,232	$	2,021
Class B: did not sell your shares	$	189	$	585	$	1,006	$	2,026
sold all your shares at
the end of the period	$	689	$	885	$	1,206	$	2,026
Class C: did not sell your shares	$	208	$	643	$	1,103	$	2,379
sold all your shares at
the end of the period	$	308	$	643	$	1,103	$	2,379

See the Appendix for additional hypothetical investment and expense information.

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Your Account

CHOOSING A SHARE CLASS

The Fund offers three classes of shares in this prospectus — Class A, Class B and Class C. Each share class has its own commission and expense structure that affects the investment return of that class. Determining which share class is best for you depends on various factors, including the amount you are investing, how long you expect to hold your investment and your personal situation.

You should consult with your financial advisor before deciding which share class is most appropriate for you. The following considerations should be part of your assessment:

•  You will pay a commission if you buy Class A, B or C shares, either at the time of investment or redemption, or through ongoing distribution commission payments (Rule 12b-1 fees) made from your investment over time, or both.

•  Class A shares require an up-front commission payment, but pay lower ongoing Rule 12b-1 fees than Class B and Class C shares. Class B and Class C shares have no up-front commission paid by the shareholder but pay higher ongoing commissions (Rule 12b-1 fees), a deferred commission is imposed on a redemption of Class B shares within six years after purchase, and a deferred commission is imposed on a redemption of Class C shares within one year of purchase. The differential between classes will vary depending on the actual investment return for any given period.

•  Class A shares can be more advantageous to an investor who intends to hold the shares for several years and invests an amount large enough to qualify for a reduced rate of initial sales commission, taking into account the commissions that investor may pay when redeeming shares of other classes. To project whether Class A shares might be more advantageous to you, you should consider, among other factors, the time period you intend to hold the shares, your initial sales commission and a comparison of the total annual expenses of Class A shares to the expenses of other share classes. Class A shares pay an ongoing annual commission (Rule 12b-1 fee) of up to 0.25% of the average value of the shares.

•  Class B shares pay an ongoing annual commission (Rule 12b-1 fee) of up to 0.75% of the average value of the shares and automatically convert to Class A shares after eight years. A Class B shareholder of the Fund whose account has a value of less than $50,000 (including for this purpose the combined value of all eligible accounts maintained by that shareholder you that would be used to determine eligibility for reduced sales charges on Class A shares) may purchase additional Class B shares of the Fund to increase the account value up to a maximum of $49,999; any additional investment by the shareholder in that Fund will be invested in Class A shares of the Fund, without regard to the normal investment minimum for Class A shares, but will be subject to the applicable Class A shares up-front commission.

•  Class C shares are generally more advantageous to an investor who intends to hold shares for only a few years. Class C shares pay an ongoing annual commission (Rule 12b-1 fee) of up to 1.00% of the average value of the shares.

•  If you invest $1 million or more, you can purchase Class A shares but not Class C shares.

The Fund also offers an additional class of shares, Class Z shares, exclusively to certain institutional and other eligible investors. Class Z shares are made available through a separate prospectus provided to institutional and other investors.

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Your Account

HOW TO BUY SHARES

Your financial advisor can help you establish an appropriate investment portfolio, buy shares and monitor your investments. When the Fund receives your purchase request in "good form," your shares will be bought at the next calculated public offering price. "Good form" means that the Fund's transfer agent has all information and documentation it deems necessary to effect your order. For example "good form" may mean that you have properly placed your order with your financial advisor or the Fund's transfer agent has received your completed application, including all necessary signatures. The Fund reserves the right to refuse a purchase order for any reason, including if the Fund believes that doing so would be in the best interest of the Fund and its shareholders. The USA PATRIOT Act may require us to obtain certain personal information from you that we will use to verify your identity. If you do not provide the information, we m ay not be able to open your account. If we are unable to verify your customer information, we reserve the right to close your account or take such other steps as we deem reasonable.

INVESTMENT MINIMUMS

The minimum initial investment for Class A, Class B and Class C shares generally is $2,500. The investment minimum is applied at the class level. For individual retirement plans (including traditional IRAs, Roth IRAs and Coverdell Education Savings Accounts) and non-omnibus group retirement accounts, the minimum initial investment is $1,000. For non-omnibus group retirement plans, the investment minimum is determined based on the plan's investment rather than on the separate investments of its individual participants. For investors establishing an automatic investment plan, the minimum initial investment is $50. There is no minimum initial investment for omnibus accounts or wrap accounts.

The minimum investment for additional purchases of Class A, Class B and Class C shares is $50 for all investors.

The Fund reserves the right to change these investment minimums. The Fund also reserves the right to refuse a purchase order for any reason, including if it believes that doing so would be in the best interest of the Fund and its shareholders. In addition, pursuant to the Trust's Agreement and Declaration of Trust, the Fund reserves the right to redeem your shares if your account falls below the minimum investment restrictions.

Please see the SAI for more details on investment minimums.

Outlined below are the various options for buying shares:

Method	Instructions
Through your financial advisor	Your financial advisor can help you establish your account and buy Fund shares on your behalf. To receive the current trading day's price, your financial advisor must receive your request prior to the close of regular trading on the New York Stock Exchange (NYSE), usually 4:00 p.m. Eastern time. Your financial advisor may charge you fees for executing the purchase for you.
By check (new account)	For new accounts, send a completed application and check made payable to the Fund to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By check (existing account)	For existing accounts, fill out and return the additional investment stub included in your account statement, or send a letter of instruction including your name, the Fund's share class and account number with a check made payable to the Fund to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By exchange	You or your financial advisor may acquire Fund shares for your account by exchanging shares you own in a different fund distributed by Columbia Management Distributors, Inc. for shares of the same class (and, in some cases, certain other classes) of the Fund at no additional cost. An exchange to another fund may incur a sales charge if the original purchase was not assessed a sales charge. To exchange by telephone, call 1-800-422-3737. Please see "How to Exchange Shares" for more information.

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Your Account

Method	Instructions
By wire	You may purchase Fund shares by wiring money from your bank account to your Fund account. To wire funds to your Fund account, call 1-800-422-3737 for wiring instructions.
By electronic funds transfer	You may purchase Fund shares by electronically transferring money from your bank account to your Fund account by calling 1-800-422-3737. An electronic funds transfer may take up to two business days to settle and must be considered in "good form." You must set up this feature prior to your telephone request. Be sure to complete the appropriate section of the application for this feature.
Automatic investment plan	You may make monthly or quarterly investments ($50 minimum) automatically from your bank account to your Fund account. You may select a pre-authorized amount to be sent via electronic funds transfer. Be sure to complete the appropriate section of the application for this feature.
Automated dollar cost averaging	You may purchase Fund shares for your account by exchanging $100 or more each month from another fund for shares of the same class of the Fund at no additional cost. Exchanges will continue so long as your fund balance is sufficient to complete the transfers. You may terminate your program or change the amount of the exchange (subject to the $100 minimum) by calling 1-800-345-6611. There may be an additional sales charge if exchanging from a money market fund. Be sure to complete the appropriate section of the account application for this feature.
By dividend diversification	You may automatically invest dividends distributed by another fund into the same class of shares (and, in some cases, certain other classes) of the Fund at no additional sales charge. There may be an additional sales charge if automatically investing dividends from a money market fund. To invest your dividends in the Fund, call 1-800-345-6611.
Through the internet	You may purchase Fund shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet purchases. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

SALES CHARGES (COMMISSIONS)

You may be subject to an initial sales charge when you purchase, or a contingent deferred sales charge (CDSC) when you sell, shares of the Fund. These sales charges are described below. In certain circumstances, the sales charge may be reduced or waived, as described below and in the SAI.

Rule 12b-1 Plan The Fund has adopted a plan under Rule 12b-1 under the Investment Company Act that permits it to pay its distributor ongoing sales and marketing fees (commissions) to support the sale and distribution of Class A, B and C shares and certain services provided to you by your financial advisor, and your financial advisor may receive all or a portion of those fees attributable to your shares. The annual fee, as a percentage of the value of the shares, is normally 0.25% for Class A, 0.75% Class B and 1.00% for Class C shares. These fees are paid out of the assets of these share classes. Over time, these fees reduce the return on your investment. Class B shares automatically convert to Class A shares after eight years, eliminating a portion of the Rule 12b-1 fee thereafter.

Financial Intermediary Payments

The Fund's distributor, investment adviser or their affiliates may make payments, from their own resources, to certain financial intermediaries, including other Bank of America affiliates, for marketing support services. For purposes of this section the term "financial intermediary" includes any broker, dealer, bank, bank trust department, registered investment adviser, financial planner, retirement plan or other third-party administrator and any other institution having a selling, services or any similar agreement with the Fund's distributor, investment adviser or one of their affiliates. These payments are generally based upon one or more of the following factors: average net assets of the mutual funds distributed by the Fund's distributor attributable to that financial intermediary, gross sales of the mutual funds distributed by the Fund's distributor attributable to that financial intermediary, reimbursement of ticket charge s (fees that a financial intermediary firm charges its representatives for effecting transactions in fund shares) or a negotiated lump sum payment.

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Your Account

While the financial arrangements may vary for each financial intermediary, the payments to any one financial intermediary are generally expected to be between 0.05% and 0.35% on an annual basis for payments based on average net assets of the Fund attributable to the financial intermediary, and between 0.10% and 0.25% on an annual basis for firms receiving a payment based on gross sales of the Fund attributable to the financial intermediary. The Fund's distributor, investment adviser or their affiliates may make payments in materially larger amounts or on a basis materially different from those described above when dealing with other affiliates of Bank of America. Such increased payments to the other Bank of America affiliate may enable the other Bank of America affiliate to offset credits that it may provide to its customers in order to avoid having such customers pay fees to multiple Bank of America entities in connection with the customer's investment in the Fund.

Payments also may be made to certain financial intermediaries, including other Bank of America affiliates, that provide investor services to retirement plans and other investment programs to compensate financial intermediaries for services they provide to such programs, including, but not limited to, sub-accounting, sub-transfer agency, similar shareholder or participant recordkeeping, shareholder or participant reporting, or shareholder or participant transaction processing. These payments for investor servicing support vary by financial intermediary but generally are not expected, with certain limited exceptions, to exceed 0.35% of the total Fund assets for Class A, B and C shares in the program on an annual basis.

The Trust's Board of Trustees has authorized the Fund to pay to any intermediary up to 0.05% of the average aggregate value of Fund shares in the intermediary's program on an annual basis for providing investor services. Charges of an intermediary in excess of that paid by the Fund will be borne by the Fund's distributor or its affiliates.

The Fund's distributor, investment adviser or their affiliates may make other payments or allow promotional incentives to financial intermediaries to the extent permitted by the rules of the Securities and Exchange Commission, the National Association of Securities Dealers and by other applicable laws and regulations.

Amounts paid by the Fund's distributor, investment adviser or their affiliates are paid out of the distributor's, investment adviser's or their affiliates' own resources and do not increase the amount paid by you or the Fund. You can find further details about the payments made by the Fund's distributor, investment adviser or their affiliates and the services provided by financial intermediaries as well as a list of the financial intermediaries to which the Fund's distributor, investment adviser or their affiliates have agreed to make marketing support payments in the Fund's SAI, which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611. Your financial intermediary may charge you fees or commissions in addition to those disclosed in this prospectus. You can ask y our financial intermediary for information about any payments it receives from the Fund's distributor, investment adviser and their affiliates and any services your financial intermediary provides, as well as fees and/or commissions it charges. In addition, depending on the financial arrangement in place at any particular time, a financial intermediary and its financial consultants also may have a financial incentive for recommending a particular fund or share class over others. You should consult with your financial adviser and review carefully any disclosure by the financial intermediary as to compensation received by your financial adviser.

Class A shares Your purchases of Class A shares are made at the public offering price for these shares. This price includes a sales charge that is based on the amount of your initial investment when you open your account. The sales charge you pay on an additional investment is based on the total amount of your purchase and the current value of your account. Shares you purchase with reinvested dividends or other distributions are not subject to a

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Your Account

sales charge. A portion of the sales charge is paid as a commission to your financial advisor on your purchase of Class A shares. The amount of the sales charge differs depending on the amount you invest as shown in the table below.

Class A Sales Charges

	Sales Charge as % of:				% of offering price
Amount of purchase	offering price		net amount invested		retained by financial advisor
Less than $50,000		5.75		6.10		5.00
$50,000 to less than $100,000		4.50		4.71		3.75
$100,000 to less than $250,000		3.50		3.63		2.75
$250,000 to less than $500,000		2.50		2.56		2.00
$500,000 to less than $1,000,000		2.00		2.04		1.75
$1,000,000 or more		0.00		0.00		0.00

In addition to the initial sales charge paid to your financial advisor and distributor, a 0.25% annual commission is paid to your financial advisor over the life of your investment out of your Fund assets as a 12b-1 fee.

The Fund's distributor may also pay additional compensation to financial advisors as an incentive for promoting the sale of shares of funds that it distributes.

Class A shares bought without an initial sales charge in accounts aggregating $1 million to $50 million at the time of purchase are subject to a 1.00% CDSC if the shares are sold within 12 months of the time of purchase. Subsequent Class A share purchases that bring your account value above $1 million (but less than $50 million) are subject to a CDSC if redeemed within 12 months of the date of purchase. The 12-month period begins on the first day of the month in which the purchase was made. The CDSC does not apply to retirement plans purchasing shares through a fee-based program.

For Class A share purchases of $1 million or more, financial advisors receive a cumulative commission from the distributor as follows:

Purchases Over $1 Million

Amount purchased	Commission %
$1 million to less than $3 million		1.00
$3 million to less than $50 million		0.50
$50 million or more		0.25

For group retirement plans, financial advisors are eligible to receive a 1.00% commission from the distributor on purchases, including those in amounts less than $1 million, that are coded as commission eligible trades. In determining the commission payable to a financial advisor in the above table, the breakpoint discount policies described in "Reduced Sales Charges (Commissions) for Larger Investments," on page 13, shall apply.

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Your Account

UNDERSTANDING CONTINGENT DEFERRED SALES CHARGES (COMMISSIONS)

Certain investments in Class A, B and C shares are subject to a CDSC, a sales charge applied at the time you sell your shares. You will pay the CDSC only on shares you sell within a certain amount of time after purchase. The CDSC generally declines each year until there is no charge for selling shares. The CDSC is applied to the net asset value at the time of purchase or sale, whichever is lower. For purposes of calculating the CDSC, the start of the holding period is the first day of the month in which the purchase was made. Shares you purchase with reinvested dividends or other distributions are not subject to a CDSC. When you place an order to sell shares, the Fund will automatically sell first those shares not subject to a CDSC and then those you have held the longest.

Reduced Sales Charges (Commissions) for Larger Investments.

A.  What are the principal ways to obtain a breakpoint discount?

There are two principal ways you may pay a lower sales charge (often referred to as "breakpoint discounts") when purchasing Class A shares of the Fund and other funds in the Columbia family of funds.

Rights of Accumulation The value of eligible accounts maintained by you and each member of your immediate family may be combined with the value of your current purchase to reach a sales charge discount level (according to the chart on the previous page) and to obtain the lower sales charge for your current purchase. To calculate the combined value of the accounts, the Fund will use the shares' current public offering price.

Statement of Intent You also may pay a lower sales charge when purchasing Class A shares by signing a Statement of Intent. By doing so, you would be able to pay the lower sales charge on all purchases made under the Statement of Intent within 13 months. As described in the chart on the previous page, the first breakpoint discount will be applied when total purchases reach $50,000. If your Statement of Intent purchases are not completed within 13 months, you will be charged the applicable sales charge on the amount you had invested to that date. To calculate the total value of your Statement of Intent purchases, the Fund will use the historic cost (i.e. dollars invested) of the shares held in each eligible account. You must retain all records necessary to substantiate historic costs because the Fund and your financial intermediary may not maintain this information.

B.  What accounts are eligible for breakpoint discounts?

The types of eligible accounts that may be aggregated to obtain one or both of the breakpoint discounts described above include:

•  Individual accounts

•  Joint accounts

•  Certain IRA accounts

•  Certain trusts

•  UTMA/UGMA accounts

For the purposes of obtaining a breakpoint discount, members of your "immediate family" include your spouse, parent, stepparent, legal guardian, child, stepchild, father in-law and mother in-law. Eligible accounts include those registered in the name of your dealer or other financial intermediary through which you own Columbia fund shares. An account is not eligible to the extent it holds an institutional class of shares of a Columbia money

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market fund or Class R shares of any Columbia fund. The value of your investment in a non-institutional class of a Columbia money market fund held in an eligible account may be aggregated with your investments in other funds in the Columbia family of funds to obtain a breakpoint discount through a Right of Accumulation. Non-institutional class investments in Columbia money market funds may also be included in the aggregation for a Statement of Intent for shares that have been charged a commission.

C.  How do I obtain a breakpoint discount?

The steps necessary to obtain a breakpoint discount depend on how your account is maintained with the Columbia family of funds. To obtain any of the above breakpoint discounts, you must notify your financial advisor at the time you purchase shares of the existence of each eligible account maintained by you or your immediate family. It is the sole responsibility of your financial advisor to ensure that you receive discounts for which you are eligible, and the Fund is not responsible for a financial advisor's failure to apply the eligible discount to your account. You may be asked by the Fund or your financial advisor for account statements or other records to verify your discount eligibility, including, where applicable, records for accounts opened with a different financial advisor and records of accounts established by members of your immediate family. If you own shares exclusively through an account maintained with the Fund's transfer agent, Columbia Management Services, Inc., you will need to provide the foregoing information to a Columbia Management Services, Inc. representative at the time you purchase shares.

D.  How can I obtain more information about breakpoint discounts?

Certain investors, including affiliates of the Fund, broker/dealers and their affiliates, investors in wrap-fee programs through fee-based advisers or certain retirement plans, certain shareholders of funds that were reorganized into other Columbia funds, and investors using the proceeds of redemptions of Fund shares or of certain Bank of America trust or similar accounts may purchase shares at a reduced sales charge or net asset value, which is the value of a fund share excluding any sales charges. CDSCs may also be waived for redemptions under a systematic withdrawal program, in connection with the death or post-purchase disability of a shareholder, certain medical expenses, charitable gifts, involuntary and tax-related redemptions, or when the selling broker/dealer has agreed to waive or return its commission. Restrictions may apply to certain accounts and certain transactions. Further information regarding these discounts ma y be found in the Fund's SAI, which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611.

Class B shares Your purchases of Class B shares are at Class B's net asset value. Purchases in Class B shares may not result in the account holding $50,000 or more of Class B shares (including for this purpose the combined value of all eligible accounts maintained by you that would be used to determine eligibility for reduced sales charges on Class A shares). In the event that an existing Class B shareholder seeks to add funds to such an account so that the balance would be in excess of $49,999, the amount in excess may be invested in Class A shares without the imposition of the minimum investment requirement for Class A shares. Such purchases of Class A shares will be subject to the applicable sales load imposed on such purchases. See "Class A Sales Charges" on page 12.

Class B shares have no front-end sales charge, but they do carry a CDSC that is imposed only on shares sold within six years of purchase. The CDSC declines over the six years and disappears in the seventh year. The distributor pays your financial advisor an up-front commission on sales of Class B shares as described in the chart below. In addition, Class B shares bear ongoing service and distribution fees that are higher than those borne by Class A shares.

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Purchases of less than $50,000:

Class B Sales Charges

Holding period after purchase	% deducted when shares are sold(1)
Through first year		5.00
Through second year		4.00
Through third year		3.00
Through fourth year		3.00
Through fifth year		2.00
Through sixth year		1.00
Longer than six years		0.00

(1)  Applied to the net asset value at the time of purchase or sale, whichever is lower.

In addition, from the annual fee of 0.75% of the value of your shares paid out of your Fund assets as Rule 12b-1 fees, the distributor receives 0.50% of the value of the shares for each of the first eight years, or an aggregate 4.00% over eight years, which will offset the commission it paid to your financial advisor. Your financial advisor is paid the remaining 0.25% as an ongoing commission for the life of your investment.

The conversion of Class B shares to Class A shares occurs automatically eight years after purchase.

Class C shares Your purchases of Class C shares are at Class C's net asset value. Although Class C shares have no front-end sales charge, they carry a CDSC of 1.00% that is applied to shares sold within the first year after they are purchased. After holding shares for one year, you may sell them at any time without paying a CDSC. The distributor pays your financial advisor an up-front commission of 1.00% on your purchase of Class C shares, for which the distributor is repaid from the ongoing annual fee of 1.00% of the value of your shares paid out of your Fund assets as Rule 12b-1 fees, which is higher than the Rule 12b-1 fees borne by Class A and Class B shares.

Class C Sales Charges

	% deducted when shares are sold(1)
Through one year		1.00
Longer than one year		0.00

(1)  Applied to the net asset value at the time of purchase or sale, whichever is lower.

A 1.00% annual commission is paid to your financial advisor and the distributor over the life of your investment out of your Fund assets.

HOW TO EXCHANGE SHARES

You may exchange your shares for shares of the same share class (and in some cases, certain other classes) of another fund distributed by Columbia Management Distributors, Inc. at net asset value. If your shares are subject to a CDSC, you will not be charged a CDSC upon the exchange. However, when you sell the shares acquired through the exchange, the shares sold may be subject to a CDSC, depending upon when you originally purchased the shares you are exchanging. For purposes of computing the CDSC, the length of time you have owned your shares will be computed from the date of your original purchase and the applicable CDSC will be the CDSC of

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the original fund. Shareholders of Columbia Acorn Funds that qualify to purchase Class A shares at net asset value may exchange their Class A shares for Class Z shares of another fund distributed by Columbia Management Distributors, Inc. (see the SAI for a description of these situations). Unless your account is part of a tax-deferred retirement plan, an exchange is a taxable event, and you may realize a gain or a loss for tax purposes. The Fund may terminate your exchange privilege if the adviser determines that your exchange activity is likely to adversely impact its ability to manage the Fund. See "Fund Policy on Trading of Fund Shares" for the Fund's policy. To exchange by telephone, call 1-800-422-3737. Please have your account and taxpayer identification numbers available when calling.

You also may exchange your shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet exchanges. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

HOW TO SELL SHARES

Your financial advisor can help you determine if and when you should sell your shares. You may sell shares of the Fund on any regular business day that the NYSE is open.

When the Fund receives your sales request in "good form," shares will be sold at the next calculated net asset value. "Good form" means that the Fund's transfer agent has all information and documentation it deems necessary to effect your order. For example, when selling shares by letter of instruction, "good form" means (i) your letter has complete instructions, the proper signatures and Medallion Signature Guarantees, (ii) if applicable, you have included any certificates for shares to be sold, and (iii) any other required documents are attached. For additional documents required for sales by corporations, agents, fiduciaries, surviving joint owners and other legal entities, please call 1-800-345-6611. Retirement plan accounts have special requirements; please call 1-800-799-7526 for more information.

The Fund will generally send proceeds from the sale to you within seven days (usually on the next business day after your request is received in "good form"). However, if you purchased your shares by check, the Fund may delay sending the proceeds from the sale of your shares for up to 10 days after your purchase to protect against checks that are returned. No interest will be paid on uncashed redemption checks. Redemption proceeds may be paid in securities rather than cash, under certain circumstances. For more information, see the paragraph "Non-Cash Redemptions" under the section "How to Sell Shares" in the SAI.

During any 90-day period for any one shareholder, the Fund is obligated to redeem shares solely in cash up to the lesser of $250,000 or 1% of the Fund's net assets. Redemptions in excess of these limits will normally be paid in cash, but may be paid wholly or partly by an in-kind distribution of securities.

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Outlined below are the various options for selling shares:

Method	Instructions
Through your financial advisor	You may call your financial advisor to place your sell order. To receive the current trading day's price, your financial advisor must receive your request prior to the close of regular trading on the NYSE, usually 4:00 p.m. Eastern time. Your financial advisor may charge you fees for executing a redemption for you.
By exchange	You or your financial advisor may sell Fund shares by exchanging from the Fund into the same share class (and, in some cases, certain other classes) of another fund distributed by Columbia Management Distributors, Inc. at no additional cost. To exchange by telephone, call 1-800-422-3737.
By telephone	You or your financial advisor may sell Fund shares by telephone and request that a check be sent to your address of record by calling 1-800-422-3737, unless you have notified the Fund of an address change within the previous 30 days. The dollar limit for telephone sales is $100,000 in a 30-day period. You do not need to set up this feature in advance of your call. Certain restrictions apply to retirement accounts. For details, call 1-800-799-7526.
By mail	You may send a signed letter of instruction or, if applicable, stock power form along with any share certificates to be sold to the address below. In your letter of instruction, note the Fund's name, share class, account number, and the dollar value or number of shares you wish to sell. All account owners must sign the letter. Signatures must be guaranteed by either a bank, a member firm of a national stock exchange or another eligible guarantor that participates in the Medallion Signature Guarantee Program for amounts over $100,000 or for alternate payee or mailing instructions. Additional documentation is required for sales by corporations, agents, fiduciaries, surviving joint owners and individual retirement account owners. For details, call 1-800-345-6611. Mail your letter of instruction to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By wire	You may sell Fund shares and request that the proceeds be wired to your bank. You must set up this feature prior to your request. Be sure to complete the appropriate section of the account application for this feature. Generally, the value of your redemption must be at least equal to $500 in order to have the sale proceeds wired to your bank. There is a $7.50 charge for wiring sale proceeds to your bank. (The transfer agent may waive this fee for omnibus and nominee accounts.) Your bank may charge additional fees for such wire transfer.
By systematic withdrawal plan	You may automatically sell a specified dollar amount or percentage of your account on a monthly, quarterly or semiannual basis and have the proceeds sent to you if your account balance is at least $5,000. The $5,000 minimum account balance requirement is waived for wrap accounts. This feature is not available if you hold your shares in certificate form. All dividend and capital gains distributions must be reinvested. Be sure to complete the appropriate section of the account application for this feature.
By electronic funds transfer	You may sell Fund shares and request that the proceeds be electronically transferred to your bank. Proceeds may take up to two business days to be received by your bank. You must set up this feature prior to your request. Be sure to complete the appropriate section of the account application for this feature.
Through the internet	You may sell Fund shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet redemptions. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

FUND POLICY ON TRADING OF FUND SHARES

The interests of the Fund's long-term shareholders may be adversely affected by certain short-term trading activity by Fund shareholders. Such short-term trading activity, when excessive, has the potential to interfere with efficient portfolio management, generate transaction and other costs, dilute the value of Fund shares held by long-term shareholders and have other adverse effects on the Fund. This type of excessive short-term trading activity is referred to herein as "market timing." For purposes of this section, The "Columbia Funds are the Columbia, Columbia Acorn Trust and Wanger Advisors Trust families of mutual funds The Columbia Funds are not intended as vehicles for market timing. The Board of Trustees of the Fund has adopted the policies and procedures set forth below with respect to frequent trading of Fund shares.

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The Fund, directly and through its agents, takes various steps designed to deter and curtail market timing. For example, if the Fund detects that any shareholder has conducted two "round trips" (as defined below) in the Fund in any 28-day period, except as noted below with respect to orders received through omnibus accounts, the Fund will reject the shareholder's future purchase orders, including exchange purchase orders, involving any Columbia fund (other than a money market fund). In addition, if the Fund determines that any person, group or account has engaged in any type of market timing activity (independent of the two-round-trip limit), the Fund may, in its discretion, reject future purchase orders by the person, group or account, including exchange purchase orders, involving the same or any other Columbia Fund, and also retains the right to modify these market timing policies at any time without prior notice.

The rights of shareholders to redeem shares of the Fund are not affected by any of the limits mentioned above. However, the Fund imposes a redemption fee on the proceeds of fund shares that are redeemed or exchanged within 60 days of their purchase.

For these purposes, a "round trip" is a purchase by any means into a Columbia Fund followed by a redemption, of any amount, by any means out of the same Columbia Fund. Under this definition, an exchange into the Fund followed by an exchange out of the Fund is treated as a single round trip. Also for these purposes, where known, accounts under common ownership or control generally will be counted together. Accounts maintained or managed by a common intermediary, such as an adviser, selling agent or trust department, generally will not be considered to be under common ownership or control.

Purchases, redemptions and exchanges made through the Columbia funds' Automatic Investment Plan, Systematic Withdrawal Plan or similar automated plans are not subject to the two-round-trip limit. Purchases, redemptions and exchanges made by Columbia Thermostat Fund are also not subject to the two-round-trip limit. The two-round-trip limit may be modified for, or may not be applied to, accounts held by certain retirement plans to conform to plan limits, considerations relating to the Employee Retirement Income Security Act of 1974 or regulations of the Department of Labor, and for certain asset allocation or wrap programs.

The practices and policies described above are intended to deter and curtail market timing in the Fund. However, there can be no assurance that these policies, individually or collectively, will be totally effective in this regard because of various factors. In particular, a substantial portion of purchase, redemption and exchange orders are received through omnibus accounts. Omnibus accounts, in which shares are held in the name of an intermediary on behalf of multiple beneficial owners, are a common form of holding shares among financial intermediaries and retirement plans. The Fund typically is not able to identify trading by a particular beneficial owner through an omnibus account, which may make it difficult or impossible to determine if a particular account is engaged in market timing. Consequently, there is the risk that the Fund may not be able to identify, deter or curtail market timing that occurs in the Fund, which ma y result in certain shareholders being able to market time the Fund while the shareholders in the Fund bear the burden of such activities.

Certain financial intermediaries (including certain retirement plan service providers whose clients include, among others, various retirement plans sponsored by Bank of America and its affiliates for the benefit of its employees (the "Bank of America retirement plan service providers")) have different policies regarding monitoring and restricting market timing in the underlying beneficial owner accounts that they maintain through an omnibus account that may be more or less restrictive than the Fund practices discussed above. In particular, the Bank of America retirement plan service providers permit the reinstatement of future purchase orders for shares of the Fund following various suspension periods. If an intermediary does not enforce the Fund's policy, the

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Your Account

intermediary must either provide data transparency to Columbia Management or Columbia Management must determine that intermediary's policy taken in its entirety provides protections to Fund shareholders that are generally commensurate with the Fund's policy.

The Fund seeks to act in a manner that it believes is consistent with the best interests of Fund shareholders in making any judgments regarding market timing. Neither the Fund nor its agents shall be held liable for any loss resulting from rejected purchase orders or exchanges.

The Fund will assess, subject to limited exceptions, a 2.00% redemption fee on the proceeds of Fund shares that are redeemed (either by selling shares or exchanging into another Columbia fund) within 60 days of their purchase. The redemption fee is paid to the Fund.

The redemption fee is imposed on Fund shares redeemed (including redemptions by exchange) within 60 days of purchase. In determining which shares are being redeemed, the Fund generally applies a first-in, first-out approach. For Fund shares acquired by exchange, the holding period prior to the exchange will not be considered in determining whether to assess the redemption fee.

The redemption fee will not be imposed if you qualify for a waiver and the Fund has received proper notification, unless the waiver is automatic as noted below. The Fund will redeem any shares that are eligible for a waiver first.

A Fund shareholder won't pay an otherwise applicable redemption fee on any of the following transactions:

•  shares sold following the death or disability (as defined in the tax code) of the shareholder, including a registered joint owner

•  shares sold by or distributions from participant directed retirement plans, such as 401(k), 403(b), 457, Keogh, profit sharing, and money purchase pension accounts, where the Fund does not have access to information about the individual participant account activity, except where the Fund has received an indication that the plan administrator is able to assess the redemption fee to the appropriate accounts (automatic)

•  shares sold by certain investment funds, including those that Columbia Management Advisors, LCC or its affiliates may manage (automatic)

•  shares sold as part of an automatic rebalancing within an asset allocation program or by certain wrap programs where the program sponsor has provided assurances reasonably satisfactory to the Fund that the program is not designed to be a vehicle for market timing

•  shares sold by accounts maintained by a financial institution or intermediary where the Fund has received information reasonably satisfactory to the Fund indicating that the financial institution or intermediary maintaining the account is unable for administrative reasons to assess the redemption fee to underlying shareholders

•  shares sold by an account which has demonstrated a hardship, such as a medical emergency, as determined in the absolute discretion of the Fund

•  shares that were purchased by reinvested dividends (automatic)

•  shares that are redeemed or exchanged through Columbia funds' Systematic Withdrawal Plan or similar affiliated or unaffiliated automated plans

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•  the following retirement plan distributions:

•  lump-sum or other distributions from a qualified corporate or self-employed retirement plan following retirement (or following attainment of age 59¹/₂ in the case of a "key employee" of a "top heavy" plan)

•  distributions from an individual retirement account (IRA) or Custodial Account under Section403(b)(7) of the tax code, following attainment of age 59¹/₂

The Fund also has the discretion to waive the 2.00% redemption fee if the Fund is in jeopardy of failing the 90% income test or losing its registered investment company qualification for tax purposes.

As described above, certain intermediaries do not assess redemption fees to certain categories of redemptions that do not present significant market timing concerns (such as automatic withdrawal plan redemptions). In these situations, the Fund's ability to assess redemption fees is generally limited by the intermediary's policies and, accordingly, no redemption fees will be assessed on such redemptions.

OTHER INFORMATION ABOUT YOUR ACCOUNT

How the Fund's Share Price is Determined The price of each class of the Fund's shares is based on its net asset value. The net asset value is determined at the close of regular trading on the NYSE, usually 4:00 p.m. Eastern time, on each business day that the NYSE is open for trading (typically Monday through Friday). Net asset value is not determined on days on which the NYSE is closed for trading.

When you request a transaction, it will be processed at the net asset value per share (plus any applicable sales charges) next determined after your request is received in "good form" by the distributor. In most cases, in order to receive that day's price, the distributor must receive your order before that day's transactions are processed. If you request a transaction through your financial advisor, your financial advisor must receive your order by the close of trading on the NYSE to receive that day's price.

The Fund determines its net asset value for each share class by dividing each class's total net assets by the number of that class's outstanding shares. In determining the net asset value, the Fund must determine the value of each security in its portfolio at the close of each trading day. Because the Fund holds securities that are traded on foreign exchanges, the value of the Fund's securities may change on days when shareholders will not be able to buy or sell Fund shares. This will affect the Fund's net asset value on the day it is next determined. Securities for which market quotations are available are valued each day at the current market value. However, where market quotations are not available, or when the adviser believes that subsequent events have made them unreliable, the Fund may use other data to determine the fair value of the securities.

The Fund has retained an independent statistical fair value pricing service to assist in the fair valuation process for securities principally traded in a foreign market in order to adjust for possible changes in value that may occur between the close of the foreign exchange and the time at which Fund shares are priced. The use of an independent fair value pricing service is intended to and may decrease the opportunities for time zone arbitrage transactions. There can be no assurance that the use of an independent fair value pricing service will successfully decrease arbitrage opportunities. If a security is valued at a "fair value," that value may be different from the last quoted market price for the security.

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You can find the daily prices of some share classes for the Fund in most major daily newspapers under the heading of "Columbia." You can find daily prices for all share classes by visiting www.columbiafunds.com.

Share Certificates Share certificates are not available for any class of shares offered by the Fund. If you currently hold previously issued share certificates, you will not be able to sell your shares until you have returned your share certificates to the transfer agent.

Dividends, Distributions, and Taxes The Fund has the potential to make the following distributions:

Types of Distributions

Dividends	Represents interest and dividends earned from securities held by the Fund, net of expenses incurred by the Fund.
Capital gains	Represents net long-term capital gains on sales of securities held for more than one year and net short-term capital gains, which are gains on sales of securities held for a one-year period or less.

Distribution Options The Fund distributes any dividends in June and December and any capital gains (including short-term capital gains) at least annually. You can choose one of the options listed in the table below for these distributions when you open your account. To change your distribution option call 1-800-345-6611.

If you do not indicate on your application or at the time your account is established your preference for handling distributions, the Fund will automatically reinvest all distributions in additional shares of the Fund.

UNDERSTANDING FUND DISTRIBUTIONS

The Fund may earn income from the securities it holds. The Fund also may realize capital gains or losses on sales of its securities. The Fund intends to distribute substantially all of its net investment income and capital gains to shareholders each year. As a shareholder, you are entitled to a portion of the Fund's income and capital gains based on the number of shares you own at the time these distributions are declared.

Distribution Options

Reinvest all distributions in additional shares of the fund

Reinvest all distributions in shares of another fund

Receive dividends in cash (see options below) and reinvest capital gains

Receive all distributions in cash (with one of the following options):

•  send the check to your address of record

•  send the check to a third-party address

•  transfer the money to your bank via electronic funds transfer

Distributions of $10 or less will automatically be reinvested in additional Fund shares. If you elect to receive distributions by check and the check is returned as undeliverable, all subsequent distributions will be reinvested in additional shares of the Fund.

Taxes Unless you are an entity exempt from income taxes or invest under a retirement account, regardless of whether you receive your distributions in cash or reinvest them in additional Fund shares, all Fund distributions are subject to federal income tax. Depending on where you live, distributions also may be subject to state and local income taxes.

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The Fund intends to elect to be treated and to qualify each year as a regulated investment company. A regulated investment company is not subject to tax at the corporate level on income and gains from investments that are distributed to shareholders in accordance with applicable law. However, the Fund's failure to qualify as a regulated investment company could result in corporate level taxation, and consequently, a reduction in income available for distribution to shareholders.

In general, any distributions of dividends, interest and short-term capital gains (determined by how long the Fund held the investments that generated them) are taxable as ordinary income, unless such dividends are "qualified dividend income" (as defined in the Internal Revenue Code) eligible for a reduced rate of tax. Properly designated distributions of long-term capital gains (determined by how long the Fund held the investments that generated them) are generally taxable as such, regardless of how long you have held your Fund shares. You will be provided with information each year regarding the amount of ordinary income and capital gains distributed to you for the previous year and any portion of your distribution which is exempt from state and local taxes. The Fund's investments in foreign securities may be subject to foreign withholding taxes. You may be entitled to claim a credit or deduction with respect to foreign taxes. Long-term capital gain rates have been reduced — in general, to 15% with lower rates applying to taxpayers in the 10% and 15% rate brackets — for taxable years beginning before January 1, 2011. Distributions are taxable to you even if they are paid from income or gains earned by the Fund before you made your investment (and thus were included in the price you paid). Your investment in the Fund may have additional personal tax implications. Please consult your tax advisor about foreign, federal, state, local or other applicable tax laws.

In addition to the dividends and capital gains distributions made by the Fund, you may realize a capital gain or loss when selling or exchanging shares of the Fund. Such transactions also may be subject to federal, state and local income tax.

Foreign Income Taxes The Fund may receive investment income from sources within foreign countries, and that income may be subject to foreign income taxes at the source. If the Fund pays non-refundable taxes to foreign governments during the year, the taxes will reduce the Fund's dividends but will still be included in your taxable income. You may be able to claim a credit or deduction on your tax return for your share of foreign taxes paid by the Fund.

Board of Trustees

The Fund is governed by its Board of Trustees. More than 75% of the Fund's Trustees are independent, meaning that they have no affiliation with the adviser or the Funds, apart from their positions as Trustees and the personal investments they may have made as private individuals.

The independent Trustees bring backgrounds in business and the professions and academia to their task of working with the Funds' officers to establish the policies and oversee the activities of the Funds. Among the Trustees' responsibilities are selecting the investment adviser for the Funds; negotiating the advisory agreements; reviewing other contracts; approving investment policies; monitoring Fund operations, performance, and costs; and nominating or selecting new Trustees.

Each Trustee serves until his or her retirement, resignation, death or removal; or otherwise as specified in the Trust's organizational documents. It is expected that every five years the Trustees will call a meeting of

22

Managing the Fund

shareholders to elect Trustees. A Trustee must retire at the end of the year in which he or she attains the age of 75. Any Trustee may be removed at a shareholders' meeting by a vote representing two-thirds of the net asset value of all shares of the Funds of the Trust. The mailing address for the Trustees and officers is 227 W. Monroe, Suite 3000, Chicago, Illinois 60606.

For more detailed information on the Board of Trustees, please refer to the SAI.

Managing the Fund

INVESTMENT ADVISER

Columbia Wanger Asset Management, L.P. (CWAM), located at 227 West Monroe Street, Suite 3000, Chicago, Illinois 60606, is the Fund's investment adviser and is responsible for the Fund's management, subject to the oversight of the Fund's Board of Trustees. CWAM and its predecessor have managed mutual funds, including the Fund, since 1992. In its duties as investment adviser, CWAM runs the Fund's day-to-day business, including making investment decisions and placing all orders for the purchase and sale of the Fund's portfolio securities.

CWAM was previously named Liberty Wanger Asset Management, L.P., and its predecessor was named Wanger Asset Management, L.P. (WAM). CWAM is a wholly owned subsidiary of Columbia Management Group, LLC, which in turn is an indirect wholly owned subsidiary of Bank of America Corporation. As of December 31, 2006, CWAM managed more than $32.9 billion in assets.

CWAM's advisory fee for managing the Fund in 2006 was 0.77% of the Fund's average daily net assets. CWAM also received an administrative fee from the Fund in 2006 of 0.04% of the Fund's average daily net assets. A discussion of the factors considered by the Fund's Board of Trustees in approving the Fund's investment advisory contract is included in the Fund's annual report to shareholders for the period ended December 31, 2006.

PORTFOLIO MANAGERS

CWAM uses a team to assist the portfolio managers in managing the Fund. Team members share responsibility for providing ideas, information and knowledge in managing the Fund, and each team member has one or more particular areas of expertise. Portfolio managers make strategic decisions and monitor and supervise individual transactions. While certain analysts recommend transactions for approval by the portfolio managers, more seasoned analysts are authorized to buy and sell securities for the Fund within the guidelines set by portfolio managers.

P. Zachary EganCo-portfolio manager
P. Zachary Egan is a vice president of the Trust and co-portfolio manager of Columbia Acorn International since May 2003. He has been CWAM's director of international research since December 2004. He has been a member of the international team since 1999.

Louis J. MendesCo-portfolio manager
Louis J. Mendes is a vice president of the Trust and co-portfolio manager of Columbia Acorn International since

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Managing the Fund

May 2003. He has been a member of the international team at CWAM since 2001. Mr. Mendes also is a vice president of Wanger Advisors Trust, and a co-portfolio manager of Wanger International Small Cap, an international mutual fund underlying variable insurance products.

The SAI provides additional information about the portfolio managers' compensation, other accounts managed and ownership of securities in the Fund.

LEGAL PROCEEDINGS

The Trust, CWAM and the trustees of the Trust (collectively, the "Columbia defendants") are named as defendants in class and derivative complaints, which were consolidated in a Multi-District Action in the federal district court for the District of Maryland on February 20, 2004 (the "MDL Action"). These lawsuits contend that defendants permitted certain investors to market time their trades in certain Columbia Acorn Funds. The MDL Action is ongoing. All claims against the Trust and its independent trustees have been dismissed; however, the interested trustees of the Trust are still parties to the MDL Action.

On March 21, 2005, a class action complaint was filed against the Trust in the Superior Court of the Commonwealth of Massachusetts seeking to rescind the contingent deferred sales charges assessed upon redemption of Class B shares of Columbia Acorn Funds due to the alleged market timing by certain shareholders of the Columbia Acorn Funds. In addition to the rescission of sales charges, plaintiffs seek recovery of actual damages, attorneys' fees and costs. The case has been transferred to the MDL Action in the federal district court of Maryland.

The Trust and CWAM are also defendants in a class action lawsuit, filed on November 13, 2003 in the Circuit Court of the Third Judicial Circuit, Madison County, Illinois, that alleges, in summary, that the Trust and CWAM exposed shareholders of Columbia Acorn International Fund to trading by market timers by allegedly (a) failing to properly evaluate daily whether a significant event affecting the value of the Fund's securities had occurred after foreign markets had closed but before the calculation of the Fund's net asset value; (b) failing to implement the Fund's portfolio valuation and share pricing policies and procedures; and (c) failing to know and implement applicable rules and regulations concerning the calculation of net asset value ("Fair Valuation Lawsuit"). On April 5, 2005, the United States Court of Appeals for the Seventh Circuit ruled that the plaintiffs' state law claims were preempted under federal law resultin g in the dismissal of plaintiffs' complaint. Plaintiffs appealed the Seventh Circuit's ruling to the United States Supreme Court. On June 15, 2006, the Supreme Court reversed the Seventh Circuit's ruling on jurisdictional grounds, and the case ultimately was remanded to the state court.

On April 4, 2006, the plaintiffs and the Columbia defendants named in the MDL Action executed an agreement in principle intended to fully resolve all of the lawsuits consolidated in the MDL Action as well as the Fair Valuation Lawsuit. The court entered a stay after the parties executed the agreement in principle. The settlement is subject to court approval.

In 2004, CWAM and the trustees of the Columbia Acorn Trust were named as defendants in certain purported shareholder class and derivative actions making claims, including claims under the Investment Company and the Investment Advisers Acts of 1940 and state law. Certain Columbia Acorn Funds were named as nominal defendants. The suits allege, inter alia, that the fees and expenses paid by the funds are excessive and that the funds' advisers and their affiliates inappropriately used fund assets to distribute the funds and for other improper purposes. On March 2, 2005, the actions were consolidated in the Massachusetts federal court as In re Columbia Entities Litigation. The plaintiffs filed a consolidated amended complaint on June 9, 2005. On November 30, 2005, the judge dismissed all claims by plaintiffs and entered final judgment in favor of the defendants. The plaintiffs appealed to the United States Court of Appeals for the First Circuit on December 30, 2005. A stipulation

24

Managing the Fund

and settlement agreement dated January 19, 2007 was filed in the First Circuit on February 14, 2007, with a joint stipulation of dismissal and motion for remand to obtain district court approval of the settlement. The joint motion was granted and the appeal was dismissed. On March 6, 2007, the case was remanded to the District Court, where the parties will seek court approval of the settlement. The terms of the proposed settlement, if approved, will require payments by the funds' adviser and/or its affiliates, including payment of plaintiffs' attorneys' fees and notice to class members. In the event that the settlement is not approved, the plaintiffs may elect to go forward with their appeal and no opinion is expressed regarding the likely outcome or financial impact of such an appeal on any fund.

On or about January 11, 2005, a putative class action lawsuit was filed in federal district court in Massachusetts against the Trust and its trustees, along with Columbia Management Advisors, LLC, the sub-administrator of the Wanger Advisors Funds and the Columbia Acorn Funds. The plaintiffs allege that the defendants failed to submit Proof of Claims in connection with settlements of securities class action lawsuits filed against companies in which the Columbia Acorn Funds held positions. The complaint seeks compensatory and punitive damages, and the disgorgement of all fees paid to Columbia Management Advisors, LLC. Plaintiffs have voluntarily dismissed the Trust and its independent trustees.

The Trust and CWAM intend to defend these suits vigorously.

As a result of these matters or any adverse publicity or other developments resulting from them, there may be increased redemptions or reduced sales of Fund shares, which could increase transaction costs or operating expenses, or have other adverse consequences for the Fund.

However, based on currently available information, the Trust believes that the likelihood that these lawsuits will have a material adverse impact on any fund is remote, and CWAM believes that the lawsuits are not likely to materially affect its ability to provide investment management services to the Fund.

Other Investment Strategies and Risks

The Fund's principal investment strategies and associated risks are described under "The Fund — Principal Investment Strategies" and "The Fund — Principal Investment Risks." This section describes other investments the Fund may make and the risks associated with them. In seeking to achieve its investment goal, the Fund may invest in various types of securities and engage in various investment techniques, which are not the principal focus of the Fund and therefore are not described in this prospectus. These types of securities and investment practices and their associated risks and the Fund's fundamental and non-fundamental investment policies are identified and discussed in the Fund's SAI, which you may obtain free of charge (see back cover). The adviser may elect not to buy any of these securities or use any of these techniques. The Fund may not always achieve its investment goal. Except as otherwise noted, approval b y the Fund's shareholders is not required to modify or change the Fund's investment strategies.

THE INFORMATION EDGE

The Fund generally invests in entrepreneurially managed smaller- and mid-sized non-U.S. companies that it believes are not as well known by financial analysts and whose position in a niche creates the opportunity for superior earnings-growth potential. CWAM may identify what it believes are important economic, social or

25

Other Investment Strategies and Risks

technological trends (for example, the growth of outsourcing as a business strategy, or the productivity gains from the increasing use of technology) and try to identify companies it thinks will benefit from these trends.

In making investments for the Fund, CWAM relies primarily on independent, internally generated research to uncover companies that may be less well known than the more popular names. To find these companies, CWAM compares growth potential, financial strength and fundamental value among companies.

Growth Potential	Financial Strength	Fundamental Value
• superior technology • innovative marketing • managerial skill • market niche • good earnings prospects • strong demand for product	• low debt • adequate working capital • conservative accounting practices • adequate profit margin	• reasonable stock price relative to growth potential and financial strength • valuable assets
The realization of this growth potential would likely produce superior performance that is sustainable over time.	A strong balance sheet gives management greater flexibility to pursue strategic objectives and is important to maintaining a competitive advantage.	Once CWAM uncovers an attractive company, it identifies a price that it believes would also make the stock a good value.

LONG-TERM INVESTING

CWAM's analysts continually screen companies and make contact with more than 1,000 companies around the globe each year. To accomplish this, CWAM analysts often talk directly to top management, vendors, suppliers and competitors.

In managing the Fund, CWAM tries to maintain lower taxes and transaction costs by investing with a long-term time horizon (at least two to five years). However, securities purchased on a long-term basis may be sold within 12 months after purchase due to changes in the circumstances of a particular company or industry, or changes in general market or economic conditions.

DERIVATIVE STRATEGIES

The Fund may enter into a number of derivative strategies, including those that employ futures, options, straddles or similar transactions to gain or reduce exposure to particular securities or markets. These strategies, commonly referred to as derivatives, involve the use of financial instruments whose values depend on, or are derived from, the value of an underlying security, index or currency. The Fund may use these strategies to adjust the Fund's sensitivity to changes in interest rates, or for other hedging purposes (i.e., attempting to offset a potential loss in one position by establishing an interest in an opposite position). Derivative strategies involve the risk that they may exaggerate a loss, potentially losing more money than the actual cost of the underlying security, or limit a potential gain. Also, with some derivative strategies there is a risk that the other party to the transaction may fail to honor its contra ct terms, causing a loss to the Fund or that the Fund may not be able to find a suitable derivative transaction counterparty, and thus may be unable to invest in derivatives altogether.

26

TEMPORARY DEFENSIVE STRATEGIES

At times, CWAM may determine that adverse market conditions make it desirable to temporarily suspend the Fund's normal investment activities. During such times, the Fund may, but is not required to, invest in cash or high-quality, short-term debt securities, without limit. Taking a temporary defensive position may prevent the Fund from achieving its investment goal.

27

Financial Highlights

The financial highlights table is intended to help you understand the Fund's financial performance. Information is shown for the Fund's last five fiscal years, which run from January 1 to December 31. Certain information in the table reflects the financial results for a single Class A, B or C share. The total returns in the table represent the return that you would have earned (or lost) on an investment in the Fund (assuming reinvestment of all dividends and distributions). This information has been derived from the Fund's financial statements, which have been audited for the years ended December 31, 2004, 2005 and 2006 by PricewaterhouseCoopers LLP, an independent registered public accounting firm, whose report, along with the Fund's financial statements, is included in the Fund's annual report. The information for the years ended December 31, 2002 and 2003 is included in the Fund's financial statements that have been audited b y another independent registered public accounting firm, whose report expressed an unqualified opinion on those financial statements and highlights. You can request a free annual report containing those financial statements by calling 1-800-345-6611.

Columbia Acorn International

	Year ended December 31,
	2006			2005			2004			2003			2002
	Class A			Class A			Class A			Class A			Class A
Net Asset Value — Beginning of Period ($)		33.20			28.75			22.45			15.32			18.35
Income from Investment Operations ($):
Net investment income(a)		0.23			0.22			0.14			0.10			0.05
Net realized and unrealized gain (loss)		10.87			5.84			6.31			7.08			(3.07	)
Total from Investment Operations		11.10			6.06			6.45			7.18			(3.02	)
Less Distributions Declared to Shareholders ($):
From net investment income		(0.32	)		(0.53	)		(0.15	)		(0.05	)		(0.01	)
From net realized gains		(3.91	)		(1.08	)		—			—			—
Total Distributions Declared to Shareholders		(4.23	)		(1.61	)		(0.15	)		(0.05	)		(0.01	)
Net Asset Value — End of Period ($)		40.07			33.20			28.75			22.45			15.32
Total return (%)(b)		34.16	(c)		21.42	(c)		28.91	(c)		46.94			(16.46	)
Ratios to Average Net Assets/Supplemental Data (%):
Expenses(d)		1.24			1.30			1.48			1.59			1.56
Net investment income(d)		0.61			0.72			0.61			0.57			0.30
Waiver/reimbursement		0.01			0.02			0.02			—			—
Portfolio turnover rate (%)		31			27			40			40			52
Net assets at end of period (000's) ($)		313,401			142,204			70,582			52,872			33,806

(a)  Per share data was calculated using average shares outstanding during the period.

(b)  Total return at net asset value assuming all distributions reinvested and no initial sales charge or contingent deferred sales charge.

(c)  Had the investment adviser and/or transfer agent not waived and/or reimbursed a portion of expenses, total return would have been reduced.

(d)  The benefits derived from custody fees paid indirectly had no impact.

28

Financial Highlights

Columbia Acorn International

	Year ended December 31,
	2006			2005			2004			2003			2002
	Class B			Class B			Class B			Class B			Class B
Net Asset Value — Beginning of Period ($)		32.71			28.18			22.07			15.11			18.22
Income from Investment Operations ($):
Net investment income (loss)(a)		(0.00	)(b)		0.02			(0.04	)		(0.02	)		(0.06	)
Net realized and unrealized gain (loss)		10.66			5.73			6.19			6.98			(3.05	)
Total from Investment Operations		10.66			5.75			6.15			6.96			(3.11	)
Less Distributions Declared to Shareholders ($):
From net investment income		(0.07	)		(0.14	)		(0.04	)		—			—
From net realized gains		(3.91	)		(1.08	)		—			—			—
Total Distributions Declared to Shareholders		(3.98	)		(1.22	)		(0.04	)		—			—
Net Asset Value — End of Period ($)		39.39			32.71			28.18			22.07			15.11
Total return (%)(c)		33.26	(d)		20.57	(d)		27.91	(d)		46.06			(17.07	)
Ratios to Average Net Assets/Supplemental Data (%):
Expenses(e)		1.89			2.01			2.27			2.24			2.21
Net investment income (loss)(e)		(0.01	)		0.08			(0.18	)		(0.10	)		(0.35	)
Waiver/reimbursement		0.02			0.02			0.02			—			—
Portfolio turnover rate (%)		31			27			40			40			52
Net assets at end of period (000's) ($)		94,165			73,572			54,752			39,800			22,560

(a)  Per share data was calculated using average shares outstanding during the period.

(b)  Rounds to less than $(0.01) per share.

(c)  Total return at net asset value assuming all distributions reinvested and no initial sales charge or contingent deferred sales charge.

(d)  Had the investment adviser and/or transfer agent not waived and/or reimbursed a portion of expenses, total return would have been reduced.

(e)  The benefits derived from custody fees paid indirectly had no impact.

29

Financial Highlights

Columbia Acorn International

	Year ended December 31,
	2006			2005			2004			2003			2002
	Class C			Class C			Class C			Class C			Class C
Net Asset Value — Beginning of Period ($)		32.68			28.19			22.06			15.11			18.21
Income from Investment Operations ($):
Net investment loss(a)		(0.05	)		(0.00	)(b)		(0.03	)		(0.01	)		(0.06	)
Net realized and unrealized gain (loss)		10.66			5.71			6.20			6.96			(3.04	)
Total from Investment Operations		10.61			5.71			6.17			6.95			(3.10	)
Less Distributions Declared to Shareholders ($):
From net investment income		(0.03	)		(0.14	)		(0.04	)		—			—
From net realized gains		(3.91	)		(1.08	)		—			—			—
Total Distributions Declared to Shareholders		(3.94	)		(1.22	)		(0.04	)		—			—
Net Asset Value — End of Period ($)		39.35			32.68			28.19			22.06			15.11
Total return (%)(c)		33.14			20.45	(d)		28.01	(d)		46.00			(17.02	)
Ratios to Average Net Assets/Supplemental Data (%):
Expenses(e)		2.01			2.09			2.24			2.24			2.21
Net investment loss(e)		(0.14	)		(0.01	)		(0.15	)		(0.06	)		(0.35	)
Waiver/reimbursement		0.01			0.02			0.02			—			—
Portfolio turnover rate (%)		31			27			40			40			52
Net assets at end of period (000's) ($)		99,425			47,325			30,547			22,990			14,575

(a)  Per share data was calculated using average shares outstanding during the period.

(b)  Rounds to less than $(0.01) per shares.

(c)  Total return at net asset value assuming all distributions reinvested and no initial sales charge or contingent deferred sales charge.

(d)  Had the investment adviser and/or transfer agent not waived and/or reimbursed a portion of expenses, total return would have been reduced.

(e)  The benefits derived from custody fees paid indirectly had no impact.

30

Appendix

Hypothetical Investment and Expense Information

The Fund is required to disclose the following supplemental hypothetical investment information, which provides additional information about the effect of the expenses paid by the Fund, including investment advisory fees and other Fund costs, on the Fund's returns over a 10-year period. The tables show the estimated expenses that would be charged on a hypothetical investment of $10,000 in each class of the Fund assuming a 5% return each year, the cumulative return after fees and expenses, and the hypothetical year-end balance after fees and expenses. The tables also assume that all dividends and distributions are reinvested and that Class B shares convert to Class A shares after eight years. The annual expense ratios used for the Fund, which are the same as those stated in the Annual Fund Operating Expenses table, are presented in the tables, and are net of any contractual fee waivers or expense reimbursements for the period of the contractual commitment. Your actual costs may be higher or lower. The tables shown below reflect the maximum initial sales charge for Class A shares but do not reflect any contingent deferred sales charges which may be payable on redemption. If contingent deferred sales charges were reflected, the "Hypothetical Year-End Balance After Fees and Expenses" amounts shown would be lower and the "Annual Fees and Expenses" amounts shown would be higher.

Columbia Acorn International — Class A Shares

Maximum Sales Charge 5.75%					Initial Hypothetical Investment Amount $10,000.00						Assumed Rate of Return 5%
Year		Cumulative Return Before Fees & Expenses			Annual Expense Ratio			Cumulative Return After Fees & Expenses			Hypothetical Year-End Balance After Fees & Expenses		Annual Fees & Expenses(1)
	1		5.00	%		1.27	%		-2.23	%(2)	$	9,776.55	$	696.93
	2		10.25	%		1.27	%		1.41	%	$	10,141.22	$	126.48
	3		15.76	%		1.27	%		5.19	%	$	10,519.49	$	131.20
	4		21.55	%		1.27	%		9.12	%	$	10,911.86	$	136.09
	5		27.63	%		1.27	%		13.19	%	$	11,318.87	$	141.17
	6		34.01	%		1.27	%		17.41	%	$	11,741.07	$	146.43
	7		40.71	%		1.27	%		21.79	%	$	12,179.01	$	151.89
	8		47.75	%		1.27	%		26.33	%	$	12,633.29	$	157.56
	9		55.13	%		1.27	%		31.05	%	$	13,104.51	$	163.44
	10		62.89	%		1.27	%		35.93	%	$	13,593.31	$	169.53
Total Gain After Fees and Expenses											$	3,593.31
Total Annual Fees and Expenses													$	2,020.72

(1)  Annual Fees and Expenses are calculated based on the average between the beginning and ending balance for each year. All information is calculated on an annual compounding basis.

(2)  Reflects deduction of the maximum initial sales charge.

31

Appendix

Columbia Acorn International — Class B Shares

Maximum Sales Charge 0.00%					Initial Hypothetical Investment Amount $10,000.00						Assumed Rate of Return 5%
Year		Cumulative Return Before Fees & Expenses			Annual Expense Ratio			Cumulative Return After Fees & Expenses			Hypothetical Year-End Balance After Fees & Expenses		Annual Fees & Expenses(1)
	1		5.00	%		1.86	%		3.14	%	$	10,314.00	$	188.92
	2		10.25	%		1.86	%		6.38	%	$	10,637.86	$	194.85
	3		15.76	%		1.86	%		9.72	%	$	10,971.89	$	200.97
	4		21.55	%		1.86	%		13.16	%	$	11,316.41	$	207.28
	5		27.63	%		1.86	%		16.72	%	$	11,671.74	$	213.79
	6		34.01	%		1.86	%		20.38	%	$	12,038.23	$	220.50
	7		40.71	%		1.86	%		24.16	%	$	12,416.23	$	227.43
	8		47.75	%		1.86	%		28.06	%	$	12,806.10	$	234.57
	9		55.13	%		1.27	%		32.84	%	$	13,283.77	$	165.67
	10		62.89	%		1.27	%		37.79	%	$	13,779.26	$	171.85
Total Gain After Fees and Expenses											$	3,779.26
Total Annual Fees and Expenses													$	2,025.83

(1)  Annual Fees and Expenses are calculated based on the average between the beginning and ending balance for each year. All information is calculated on an annual compounding basis.

32

Appendix

Columbia Acorn International — Class C Shares

Maximum Sales Charge 0.00%					Initial Hypothetical Investment Amount $10,000.00						Assumed Rate of Return 5%
Year		Cumulative Return Before Fees & Expenses			Annual Expense Ratio			Cumulative Return After Fees & Expenses			Hypothetical Year-End Balance After Fees & Expenses		Annual Fees & Expenses(1)
	1		5.00	%		2.05	%		2.95	%	$	10,295.00	$	208.02
	2		10.25	%		2.05	%		5.99	%	$	10,598.70	$	214.16
	3		15.76	%		2.05	%		9.11	%	$	10,911.36	$	220.48
	4		21.55	%		2.05	%		12.33	%	$	11,233.25	$	226.98
	5		27.63	%		2.05	%		15.65	%	$	11,564.63	$	233.68
	6		34.01	%		2.05	%		19.06	%	$	11,905.79	$	240.57
	7		40.71	%		2.05	%		22.57	%	$	12,257.01	$	247.67
	8		47.75	%		2.05	%		26.19	%	$	12,618.59	$	254.97
	9		55.13	%		2.05	%		29.91	%	$	12,990.84	$	262.50
	10		62.89	%		2.05	%		33.74	%	$	13,374.07	$	270.24
Total Gain After Fees and Expenses											$	3,374.07
Total Annual Fees and Expenses													$	2,379.27

(1)  Annual Fees and Expenses are calculated based on the average between the beginning and ending balance for each year. All information is calculated on an annual compounding basis.

33

Notes

34

Notes

35

FOR MORE INFORMATION

Additional information about the Fund's investments is available in the Fund's semiannual and annual reports to shareholders. The annual report contains a discussion of the market conditions and investment strategies that significantly affected the Fund's performance during its last fiscal year.

You may wish to read the SAI for more information on the Fund and the securities in which it invests. The SAI is incorporated into this prospectus by reference, which means that it is considered to be part of this prospectus.

You can get free copies of annual and semiannual reports and the SAI, request other information and discuss your questions about the Fund by visiting www.columbiafunds.com or by writing or calling the Fund's transfer agent at:

Columbia Management Services, Inc.
P.O. Box 8081
Boston, MA 02266-8081
1-800-345-6611

Text-only versions of all Fund documents can be viewed online or downloaded from the EDGAR database on the Securities and Exchange Commission internet site at www.sec.gov.

You can review and copy information about the Fund, including the SAI, by visiting the following location, and you can obtain copies upon payment of a duplicating fee, by electronic request at the e-mail address publicinfo@sec.gov or by writing the:

Public Reference Room
Securities and Exchange Commission
Washington, DC 20549-0102

Information on the operation of the Public Reference Room may be obtained by calling 1-202-942-8090.

Investment Company Act file number:
Columbia Acorn Trust: 811-01829
•  Columbia Acorn International

©2007 Columbia Management Distributors, Inc.
One Financial Center, Boston, MA 02111-2621
800.426.3750 www.columbiafunds.com

INT-36/130111-0507

Columbia^SM

Acorn International^®  Prospectus, May 1, 2007

Class Z Shares

Advised by Columbia Wanger Asset Management, L.P.

TABLE OF CONTENTS

THE FUND	2
Investment Goal	2
Principal Investment Strategies	2
Principal Investment Risks	2
Portfolio Holdings Disclosure	4
Performance History	4
Your Expenses	6
YOUR ACCOUNT	8
How to Buy Shares	8
Eligible Investors	9
Sales Charges (Commissions)	10
How to Exchange Shares	11
How to Sell Shares	12
Fund Policy on Trading of Fund Shares and Redemption Fees	13
Financial Intermediary Payments	16
Other Information About Your Account	17
BOARD OF TRUSTEES	19
MANAGING THE FUND	20
Investment Adviser	20
Portfolio Managers	20
Legal Proceedings	21
OTHER INVESTMENT STRATEGIES AND RISKS	22
The Information Edge	22
Long-Term Investing	23
Derivative Strategies	23
Temporary Defensive Strategies	24
FINANCIAL HIGHLIGHTS	25
APPENDIX	26

Only eligible investors may purchase Class Z shares. See "Your Account — Eligible Investors" for more information.

Although these securities have been registered with the Securities and Exchange Commission, the Commission has not approved or disapproved any shares offered in this prospectus or determined whether this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Acorn International^® is a trademark owned and registered by Columbia Acorn Trust, Columbia, Columbia Management^® and Columbia Management Services, Inc. are service marks owned and/or registered by Bank of America.

The Fund

INVESTMENT GOAL

Columbia Acorn International (Acorn International^®) seeks to provide long-term growth of capital.

PRINCIPAL INVESTMENT STRATEGIES

Acorn International generally invests in stocks of non-U.S. small- and medium-sized companies. The Fund generally invests in the stocks of companies based outside the United States with market capitalizations of less than $5 billion at the time of initial purchase. As long as a stock continues to meet the Fund's other investment criteria, the Fund may choose to hold a stock even if the issuing company's capitalization grows beyond a $5billion capitalization.

Acorn International believes that smaller companies, particularly outside the United States, that are not as well known by financial analysts, may offer higher return potential than the stocks of larger companies.

Acorn International typically looks for companies with:

•  A strong business franchise that offers growth potential.

•  Products and services that give the company a competitive advantage.

•  A stock price the Fund's investment adviser believes is reasonable relative to the assets and earning power of the company.

Acorn International is an international fund and invests the majority (under normal market conditions, at least 75%) of its total assets in the stocks of foreign companies based in developed markets (for example, Japan, Canada and the United Kingdom) and emerging markets (for example, Mexico, Brazil and Korea).

Additional strategies that are not principal investment strategies and the risks associated with them are described later in this prospectus under "Other Investment Strategies and Risks."

PRINCIPAL INVESTMENT RISKS

The principal risks of investing in the Fund are described below. There are many circumstances (including additional risks that are not described here) that could prevent the Fund from achieving its investment goal. You may lose money by investing in the Fund.

Management risk means that the adviser's investment decisions might produce losses or cause the Fund to underperform when compared to other funds with a similar investment goal. Market risk means that security prices in a market, sector or industry may fall, reducing the value of your investment. Because of management and market risk, there is no guarantee that the Fund will achieve its investment goal or perform favorably among comparable funds.

Since the Fund purchases equity securities, it is subject to equity risk. This is the risk that stock prices will fall over short or extended periods of time. Although the stock market historically has outperformed other asset classes over the long term, the stock market tends to move in cycles. Individual stock prices may fluctuate drastically from day-to-day and may underperform other asset classes over an extended period of time. Individual companies may report poor results or be negatively affected by industry and/or economic trends and developments. The prices of securities issued by such companies may suffer a decline in response. These price movements may result from factors affecting individual companies, industries or the securities market as a whole.

2

The Fund

Because the Fund invests in stocks, the price of its shares — its net asset value (NAV) per share — fluctuates daily in response to changes in the market value of stocks.

Sector risk is inherent in the Fund's investment strategy. Companies that are in different but closely related industries are sometimes described as being in the same broad economic sector. The values of stocks of different companies in a market sector may be similarly affected by particular economic or market events. Although the Fund does not intend to focus on any particular sector, at times the Fund may have a large portion of its assets invested in a particular sector.

Foreign securities are subject to special risks. Foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the dollar value of foreign securities denominated in foreign currencies and U.S. dollars, without a change in the intrinsic value of those securities. The liquidity of foreign securities may be more limited than that of domestic securities, which means that the Fund may, at times, be unable to sell foreign securities at desirable prices. Brokerage commissions, custodial fees and other fees are generally higher for foreign investments. In addition, foreign governments may impose withholding taxes that would reduce the amount of income and capital gains available to distribute to shareholders. Other risks include possible delays in the settlement of transactions or in the notification of income; less publicly av ailable information about companies; the impact of political, social or diplomatic events; possible seizure, expropriation or nationalization of the company or its assets; and possible imposition of currency exchange controls.

Market timers. Because the Fund invests predominantly in foreign securities, the Fund may be particularly susceptible to market timers. Market timers generally attempt to take advantage of the way the Fund prices its shares by trading based on market information they expect will lead to a change in the Fund's net asset value on the next pricing day. Market timing activity may be disruptive to Fund management and, since a market timer's profits are effectively paid directly out of the Fund's assets, may negatively impact the investment returns of other shareholders. Although the Fund has adopted certain policies and methods intended to identify and discourage frequent trading based on this strategy, it cannot ensure that all such activity can be identified or terminated.

Investments in emerging markets are subject to additional risk. The risks of foreign investments are typically increased in less developed countries, which are sometimes referred to as emerging markets. For example, political and economic structures in these countries may be new and developing rapidly, which may cause instability. These countries are also more likely to experience high levels of inflation, deflation or currency devaluations, which could hurt their economies and securities markets.

Small- or mid-cap companies may be more susceptible to market downturns, and their prices could be more volatile than large-cap companies. These companies are more likely than larger companies to have limited product lines, operating histories, markets or financial resources. They may depend heavily on a small management team and may trade less frequently, may trade in smaller volumes and may fluctuate more sharply in price than stocks of larger companies. In addition, such companies may not be widely followed by the investment community, which can lower the demand for their stocks.

An investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

3

The Fund

PORTFOLIO HOLDINGS DISCLOSURE

A description of the Fund's policies and procedures with respect to the disclosure of its portfolio securities is available in the Fund's Statement of Additional Information (SAI), which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611.

The Fund posts its complete portfolio holdings as of month-end at www.columbiafunds.com approximately 30-40 calendar days after such month-end. Additionally, the Fund discloses its top 15 month-end portfolio holdings at www.columbiafunds.com on or about 15 calendar days following such month-end.

Once posted, the above information will remain available on the website until at least the date on which the Fund files a Form N-CSR or Form N-Q for the period that includes the date as of which the information is current.

PERFORMANCE HISTORY

The bar chart below shows the Fund's calendar-year total returns (before taxes) for its Class Z shares. The performance table following the bar chart shows how the Fund's average annual total returns for Class Z shares compare with broad measures of market performance for one year, five years and ten years. The chart and table are intended to illustrate some of the risks of investing in the Fund by showing changes in the Fund's performance from year to year. All returns include the reinvestment of dividends and distributions. As with all mutual funds, past performance (before and after taxes) does not predict the Fund's future performance.

UNDERSTANDING PERFORMANCE

Calendar Year Total Returns show the Fund's Class Z share performance for each of the last ten complete calendar years. Those returns include the effects of Fund expenses.

Average Annual Total Returns are a measure of the Fund's Class Z average performance over the past one-year, five-year and ten-year periods. They include the effects of Fund expenses.

The Fund's returns are compared to the S&P/Citigroup EMI Global ex-U.S. Index, the Morgan Stanley Europe, Australasia and Far East Index (EAFE) and the S&P/Citigroup Global ex-U.S. Cap Range $500M-$5B. The S&P/Citigroup EMI Global ex-U.S., the Fund's primary benchmark, is an index of the bottom 20% of institutionally investable capital of developed and emerging countries (after 9/30/1994), selected by the index sponsor, outside the United States. The Morgan Stanley Capital International (MSCI) Europe, Australasia, Far East (EAFE) Index is a free float-adjusted market capitalization index that is designed to measure developed market equity performance, excluding the U.S. and Canada. The S&P/Citigroup Global ex-U.S. Cap Range $500M-$5B is a subset of the broad market selected by the index sponsor representing the small- and mid-cap developed and emerging markets, excluding the United States. Unlike the Fund, indice s are not investments, do not incur fees, expenses or taxes, and are not professionally managed.

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The Fund

Calendar Year Total Returns (Class Z)⁽¹⁾

(1)  The Fund's performance in 1999 was achieved during a period of unusual market conditions.

For the periods shown in bar chart:
Best quarter: 4th quarter 1999, +41.63%
Worst quarter: 3rd quarter 2002, -19.67%

After tax returns are calculated using the highest historical individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on each investor's own tax situation and may differ from those shown. After-tax returns may not be relevant to investors who hold Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Average Annual Total Returns — for periods ended December 31, 2006

Share Class	1 Year		5 Year		10 Years(1)
Class Z (%)
Return Before Taxes		34.53		21.35		13.15
Return After Taxes on Distributions		32.08		20.68		12.01
Return After Taxes on Distributions and Sale of Fund Shares		24.72		18.86		11.26
Indices
S&P/Citigroup EMI Global ex-U.S. (%)		30.83		24.39		10.65
MSCI EAFE (%)		26.34		14.98		7.71
S&P/Citigroup Global ex-U.S. Cap Range $500M-$5B (%)		26.70		24.15		10.86

(1)  The Fund's performance in 1999 was achieved during a period of unusual market conditions.

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The Fund

YOUR EXPENSES

Expenses are one of several factors to consider before you invest in a mutual fund. The tables below describe the fees and expenses you may pay when you buy, hold and sell shares of the Fund.

UNDERSTANDING EXPENSES

Annual Fund Operating Expenses are paid by the Fund. They include management and administration fees and other expenses that generally include, but are not limited to, transfer agency, custody, and legal fees as well as costs related to state registration and printing of Fund documents. The specific fees and expenses that make up the Fund's other expenses will vary from time to time and may include fees or expenses not described here. The Fund will likely incur portfolio transaction costs that are in addition to the total annual fund operating expenses disclosed in the fee table. These transaction costs are made up of all costs that are associated with trading securities for the Fund's portfolio and include, but are not limited to, brokerage commissions and market spreads, as well as potential changes to the price of a security due to the Fund's effor ts to purchase or sell it. While certain elements of transaction costs are readily identifiable and quantifiable, other elements that can make up a significant amount of the Fund's transaction costs are not. Higher transaction costs reduce the Fund's returns.

Shareholder Fees (commissions paid directly from your investment)

Maximum sales charge (load) on purchases (%) (as a percentage of the offering price)	None
Maximum deferred sales charge (load) on redemptions (%) (as a percentage of the lesser of purchase price or redemption price)	None
Redemption fee (%) (as a percentage of amount redeemed, if applicable)	2.00	(1)(2)

(1)  Charged only when selling or exchanging shares you have owned for 60 days or less. For more information, see "Fund Policy on Trading of Fund Shares and Redemption Fees" below.

(2)  There is a $7.50 charge for wiring sale proceeds to your bank.

Annual Fund Operating Expenses (deducted directly from Fund assets)

Management fees(1) (%)	0.77
Distribution and service (12b-1) fees (%)	None
Other expenses(2) (%)	0.17
Total annual fund operating expenses (%)	0.94

(1)  The Fund pays an investment advisory fee of 0.77%. The Fund and its adviser have implemented a breakpoint schedule for the Fund's investment advisory fees. The investment advisory fee rates charged to the Fund will decline as Fund assets grow and will continue to be based on a percentage of the Fund's average daily assets. The annual fee schedule for the Fund is as follows: 1.19% for assets up to $100 million; 0.94% for assets in excess of $100 million and up to $500 million; 0.74% for assets in excess of $500 million. In addition to the management fee, the Fund and the other funds of Columbia Acorn Trust (the "Trust") pay the adviser an administrative fee based on the average daily aggregate net assets of the Trust at the following annual rates: 0.05% of net assets up to $8 billion; 0.04% of the next $8 billion; and 0.03% of net assets in excess of $16 billion. Based on the Trust's average daily net assets as of December 31, 2006, the administrative fee would be at a rate of 0.04% and is included in "Other expenses."

(2)  "Other expenses" have been restated to reflect contractual changes to the transfer agency fees paid by the Fund.

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The Fund

Example Expenses help you compare the cost of investing in the Fund to the cost of investing in other mutual funds. It uses the following hypothetical conditions:

•  $10,000 initial investment

•  5% total return for each year

•  Fund operating expenses remain the same

•  Reinvestment of all dividends and distributions

Example Expenses for a $10,000 investment (your actual costs may be higher or lower)

1 Year		3 Years		5 Years		10 Years
$	96	$	300	$	520	$	1,155

See the Appendix for additional hypothetical investment and expense information.

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HOW TO BUY SHARES

If you are an eligible investor (described on page 9), when the Fund receives your purchase request in "good form," your shares will be bought at the next calculated price. "Good form" means that the Fund's transfer agent has all information and documentation it deems necessary to effect your order. For example "good form" may mean that you have properly placed your order with Columbia Management Services, Inc. or your financial advisor or the Fund's transfer agent has received your completed application, including all necessary signatures. The Fund reserves the right to refuse a purchase order for any reason, including if the Fund believes that doing so would be in the best interest of the Fund and its shareholders. The USA PATRIOT Act may require us to obtain certain personal information from you that we will use to verify your identity. If you do not provide the information, we may not be able to open your account. If we are unable to verify your customer information, we reserve the right to close your account or take such other steps as we deem reasonable.

You or your financial advisor may acquire shares of the Fund for your account by exchanging shares you own in a different fund distributed by Columbia Management Distributors, Inc. for shares of the same class or Class A of the Fund at no additional cost. To exchange by telephone, call 1-800-422-3737. Please see "How to Exchange Shares" for more information.

Outlined below are the various options for buying shares:

Method	Instructions
Through your financial advisor	Your financial advisor can help you establish your account and buy Fund shares on your behalf. To receive the current trading day's price, your financial advisor must receive your request prior to the close of regular trading on the New York Stock Exchange (NYSE), usually 4:00 p.m. Eastern time. Your financial advisor may charge you fees for executing the purchase for you.
By check (new account)	For new accounts, send a completed application and check made payable to the Fund to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By check (existing account)	For existing accounts, fill out and return the additional investment stub included in your account statement, or send a letter of instruction including your name, Fund share class and account number with a check made payable to the Fund to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By exchange	You may acquire Fund shares for your account by exchanging shares you own in a different fund distributed by Columbia Management Distributors Inc. for shares of the same class or Class A of the Fund at no additional cost. Toexchange by telephone, call 1-800-422-3737. Please see "How to Exchange Shares" for more information.
By wire	You may purchase Fund shares by wiring money from your bank account to your Fund account. To wire funds to your Fund account, call 1-800-422-3737 for wiring instructions.
By electronic funds transfer	You may purchase Fund shares by electronically transferring money from your bank account to your Fund account by calling 1-800-422-3737. An electronic funds transfer may take up to two business days to settle and must be considered in "good form." You must set up this feature prior to your telephone request. Be sure to complete the appropriate section of the application for this feature.
Automatic investment plan	You may make monthly or quarterly investments ($50 minimum) automatically from your bank account to your Fund account. You may select a pre-authorized amount to be sent via electronic funds transfer. Be sure to complete the appropriate section of the application for this feature.
Automated dollar cost averaging	You may purchase Fund shares for your account by exchanging $100 or more each month from another fund for shares of the same class of the Fund at no additional cost. Exchanges will continue so long as your fund balance is sufficient to complete the transfers. You may terminate your program or change the amount of the exchange (subject to the $100 minimum) by calling 1-800-345-6611. There may be an additional sales charge if exchanging from a money market fund. Be sure to complete the appropriate section of the account application for this feature.
By dividend diversification	You may automatically invest dividends distributed by another fund into the same class of share (and, in some cases, certain other classes) of the Fund at no additional sales charge. There may be an additional sales charge if automatically investing dividends from a money market fund. To invest your dividends in the Fund, call 1-800-345-6611.

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Your Account

Method	Instructions
Through the internet	You may purchase Fund shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet purchases. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1 800-345-6611.

ELIGIBLE INVESTORS

Only certain eligible investors may purchase Class Z shares of the Fund (Eligible Investor), directly or by exchange. Please read the following section for a more detailed description of the eligibility requirements. The Eligible Investors described below are subject to different minimum initial investment requirements.

Eligibility for certain waivers, exemptions or share classes by new or existing investors may not be readily available or accessible through all intermediaries or all types of accounts offered by a broker-dealer, bank, third-party administrator or other financial institution (each commonly referred to as an "intermediary"). Accessibility of these waivers through a particular intermediary also may change at any time. If you believe you are eligible to purchase shares under a specific exemption, but are not permitted by your intermediary to do so, please contact your intermediary. You may be asked to provide information, including account statements and other records, regarding your eligibility.

Eligible Investors and their applicable investment minimums are as follows:

No minimum initial investment

•  Any group retirement plan, holding Fund shares in an omnibus manner, for which an intermediary or other entity provides services and is not compensated by the Funds for those services, other than payments for shareholder servicing or sub-accounting performed in place of the transfer agent.

•  Any person investing all or part of the proceeds of a distribution, rollover or transfer of assets into a Columbia Management Individual Retirement Account from any deferred compensation plan which was a shareholder of any of the funds of Columbia Acorn Trust (formerly named Liberty Acorn Trust) on September 29, 2000, in which the investor was a participant and through which the investor invested in one or more of the funds of Columbia Acorn Trust immediately prior to the distribution, transferor rollover.

$1,000 minimum initial investment (by purchase, exchange or transfer)

•  Any individual retirement account of an Eligible Investor; or

•  Any group retirement plan, not holding Fund shares in an omnibus manner, for which an intermediary or other entity provides services and is not compensated by the Fund for those services, other than compensation for shareholder servicing or sub-accounting performed in place of the transfer agent.

$2,500 minimum initial investment (by purchase, exchange or transfer)

•  Any shareholder (as well as any family member of a shareholder or person listed on an account registration for any account of the shareholder) of a fund distributed by Columbia Management Distributors, Inc. (CMD) (i) who holds Class Z shares; (ii) who holds shares issued upon conversion of Primary A shares held prior to August 22, 2005; (iii) who holds Class A shares that were obtained by

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Your Account

exchange of Class Z shares; or (iv) who holds no-load shares issued upon the merger of a fund distributed by CMD;

•  Any trustee or director (or family member of a trustee or director) of any fund distributed by CMD;

•  Any employee (or family member of an employee) of Bank of America Corporation or a subsidiary;

•  Any investor participating in an account offered by an intermediary or other entity that provides services to such an account, is paid an asset-based fee by the investor and is not compensated by the Funds for those services, other than payments for shareholder servicing or sub-accounting performed in place of the Fund's transfer agent (each investor purchasing through an intermediary must independently satisfy the minimum investment requirement noted above);

•  Any client of Bank of America Corporation or a subsidiary purchasing through an asset management company, trust, fiduciary, retirement plan administration or similar arrangement with Bank of America Corporation or the subsidiary;

•  Any investor purchasing through a Columbia Management state tuition plan organized under Section 529 of the Internal Revenue Code;

•  Any institutional investor which is a corporation, partnership, trust, foundation, endowment, institution, government entity, or similar organization; which meets the respective qualifications for an accredited investor, as defined under the Securities Act of 1933; or

•  Certain financial institutions and intermediaries, such as insurance companies, trust companies, banks, endowments, investment companies or foundations, purchasing shares for its own account, including Bank of America Corporation, its affiliates, or subsidiaries.

The investment minimum is applied at the class level. For group retirement plans, the investment minimum is determined based on the amount of the plan's investment rather than that of its individual participants. The Fund may establish exclusions from the investment minimum from time to time that it deems appropriate and consistent with the interests of shareholders. Please see the Statement of Additional Information for details on these exclusions.

The Fund reserves the right to change the criteria for eligible investors and the investment minimums. No minimum investment applies to accounts participating in the automatic investment plan; however, each investment requires a $50 minimum purchase. The Fund also reserves the right to refuse a purchase order for any reason, including if it believes that doing so would be in the best interest of the Fund and its shareholders. Finally, pursuant to the Trust's Agreement and Declaration of Trust, the Fund reserves the right to redeem your shares if your account falls below the minimum investment requirements.

SALES CHARGES (COMMISSIONS)

Your purchases of Class Z shares are at net asset value, which is the value of a Class Z share excluding any sales charge. Class Z shares are not subject to an initial sales charge when purchased, or a contingent deferred sales charge when sold.

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Your Account

CHOOSING A SHARE CLASS

The Fund offers one class of shares in this prospectus — Class Z.

The Fund also offers three additional classes of shares — Class A, B and C shares are available through a separate prospectus. Each other share class has its own sales charge and expense structure.

Broker-dealers, investment advisers or financial planners selling mutual fund shares may offer their clients more than one class of shares in a fund with different pricing options. This allows you and your financial advisor to choose among different types of sales charges and different levels of ongoing operating expenses, depending on the investment programs your financial advisor offers. Investors should consider carefully any separate transactions and other fees charged by these programs in connection with investing in any available share class before selecting a share class.

Determining which share class is best for you depends on the dollar amount you are investing and the number of years for which you are willing to invest. Based on your personal situation, your financial advisor can help you decide which class of shares makes the most sense for you. In general, anyone who is eligible to purchase Class Z shares, which do not incur Rule 12b-1 fees or sales charges, should do so in preference over other classes.

If you purchase Class Z shares of the Fund through certain intermediaries, they may charge a fee for their services. They may also place limits on your ability to use services the Fund offers. There are no sales charges or limitations if you purchase shares directly from the Fund, except as described in this prospectus.

If an intermediary is an agent or designee of the Fund, orders are processed at the net asset value next calculated after the intermediary receives the order. The intermediary must segregate any orders it receives after the close of regular trading on the NYSE and transmit those orders separately for execution at the net asset value next determined.

HOW TO EXCHANGE SHARES

Generally, you may exchange your shares for Class Z or Class A (only if Class Z is not offered) shares of another fund distributed by CMD at net asset value. However, if you exchange shares of Columbia Acorn International that you have owned 60 days or less for shares of a fund distributed by CMD that does not have a redemption fee (including Columbia Acorn Fund, Columbia Acorn USA, Columbia Acorn Select and Columbia Thermostat Fund), the Fund will charge you a redemption fee of 2% of the redemption proceeds. Exchanges between Columbia Acorn International and Columbia Acorn International Select (or a fund distributed by CMD that has a redemption fee) will not be subject to the 2% redemption fee. You also may exchange your Class Z shares of any Fund for Class Z shares or, if there are no Class Z shares, Class A shares of certain other funds distributed by CMD at net asset value without a sales charge. Unless your account is part of a tax-deferred retirement plan, an exchange is a taxable event, and you may realize a gain or a loss for tax purposes. The Funds may terminate your exchange privilege if the adviser determines that your exchange activity is likely to adversely impact its ability to manage the Funds. See "Fund Policy on Trading of Fund Shares and Redemption Fees" for the Fund's policy. To exchange by telephone, call 1-800-422-3737. Please have your account and taxpayer identification numbers available when calling.

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Your Account

You also may exchange your shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet exchanges. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

HOW TO SELL SHARES

You may sell shares of the Fund on any regular business day that the NYSE is open.

When the Fund receives your sales request in "good form," shares will be sold at the next calculated net asset value. "Good form" means that the Fund's transfer agent has all information and documentation it deems necessary to effect your order. For example, when selling shares by letter of instruction, "good form" means (i) your letter has complete instructions, the proper signatures and Medallion Signature Guarantees, and (ii) any other required documents are attached. For additional documents required for sales by corporations, agents, fiduciaries, surviving joint owners and other legal entities, please call 1-800-345- 6611. Retirement plan accounts have special requirements; please call 1-800-799-7526 for more information.

The Fund will generally send proceeds from the sale to you within seven days (usually on the next business day after your request is received in "good form"). However, if you purchased your shares by check, the Fund may delay sending the proceeds from the sale of your shares for up to 10 days after your purchase to protect against checks that are returned. No interest will be paid on uncashed redemption checks. Redemption proceeds may be paid in securities, rather than cash, under certain circumstances. For more information, see the paragraph "Non-Cash Redemptions" under the section "How to Sell Shares" in the SAI.

During any 90-day period for any one shareholder, the Fund is obligated to redeem shares solely in cash up to the lesser of $250,000 or 1% of the Fund's net assets. Redemptions in excess of these limits will normally be paid in cash, but may be paid wholly or partly by an in-kind distribution of securities.

Outlined below are the various options for selling shares:

Method	Instructions
Through your financial advisor	You may call your financial advisor to place your sell order. To receive the current trading day's price, your financial advisor must receive your request prior to the close of regular trading on the NYSE, usually 4:00 p.m. Eastern time. Your financial advisor may charge you fees for executing a redemption for you.
By exchange	You or your financial advisor may sell Fund shares by exchanging from the Fund into Class Z shares or Class A shares (only if Class Z is not offered) of another fund distributed by Columbia Management Distributors, Inc. at no additional cost. To exchange by telephone, call 1-800-422-3737.
By telephone	You or your financial advisor may sell Fund shares by telephone and request that a check be sent to your address of record by calling 1-800-422-3737, unless you have notified the Fund of an address change within the previous 30 days. The dollar limit for telephone sales is $100,000 in a 30-day period. You do not need to set up this feature in advance of your call. Certain restrictions apply to retirement accounts. For details, call 1-800-799-7526.
By mail	You may send a signed letter of instruction to the address below. In your letter of instruction, note the Fund's name, share class, account number, and the dollar value or number of shares you wish to sell. All account owners must sign the letter. Signatures must be guaranteed by either a bank, a member firm of a national stock exchange or another eligible guarantor that participates in the Medallion Signature Guarantee Program for amounts over $100,000 or for alternate payee or mailing instructions. Additional documentation is required for sales by corporations, agents, fiduciaries, surviving joint owners and individual retirement account owners. For details, call 1-800-345-6611. Mail your letter of instruction to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.

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Your Account

Method	Instructions
By wire	You may sell Fund shares and request that the proceeds be wired to your bank. You must set up this feature rior to your request. Be sure to complete the appropriate section of the account application for this feature. Generally, the value of your redemption must be at least equal to $500 in order to have the sale proceeds wired to your bank. There is a $7.50 charge for wiring sale proceeds to your bank. (The transfer agent may waive this fee for omnibus and nominee accounts.) Your bank may charge additional fees for such wire transfer.
By systematic withdrawal plan	You may automatically sell a specified dollar amount or percentage of your account on a monthly, quarterly or semiannual basis and have the proceeds sent to you if your account balance is at least $5,000. The $5,000 minimum account balance requirement has been waived for wrap accounts. All dividend and capital gains distributions must be reinvested. Be sure to complete the appropriate section of the account application for this feature.
By electronic funds transfer	You may sell Fund shares and request that the proceeds be electronically transferred to your bank. Proceeds may take up to two business days to be received by your bank. You must set up this feature prior to your request. Be sure to complete the appropriate section of the account application for this feature.
Through the internet	You may sell Fund shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet redemptions. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1 800-345-6611.

FUND POLICY ON TRADING OF FUND SHARES AND REDEMPTION FEES

The interests of the Fund's long-term shareholders may be adversely affected by certain short-term trading activity by Fund shareholders. Such short-term trading activity, when excessive, has the potential to interfere with efficient portfolio management, generate transaction and other costs, dilute the value of Fund shares held by long-term shareholders and have other adverse effects on the Fund. This type of excessive short-term trading activity is referred to herein as "market timing." For purposes of this section "Columbia Funds" are the Columbia, Columbia Acorn Trust and Wanger Advisors Trust families of mutual funds. The Columbia Funds are not intended as vehicles for market timing. The Board of Trustees of the Fund has adopted the policies and procedures set forth below with respect to frequent trading of Fund shares.

The Fund, directly and through its agents, takes various steps designed to deter and curtail market timing. For example, if the Fund detects that any shareholder has conducted two "round trips" (as defined below) in the Fund in any 28-day period, except as noted below with respect to orders received through omnibus accounts, the Fund will reject the shareholder's future purchase orders, including exchange purchase orders, involving any Columbia fund (other than a money market fund). In addition, if the Fund determines that any person, group or account has engaged in any type of market timing activity (independent of the two-round-trip limit), the Fund may, in its discretion, reject future purchase orders by the person, group or account, including exchange purchase orders, involving the same or any other Columbia fund, and also retains the right to modify these market timing policies at any time without prior notice.

The rights of shareholders to redeem shares of the Fund are not affected by any of the limits mentioned above. However, the Fund imposes a redemption fee on the proceeds of Fund shares that are redeemed or exchanged within 60 days of their purchase.

For these purposes, a "round trip" is a purchase by any means into a Columbia fund followed by a redemption, of any amount, by any means out of the same Columbia fund. Under this definition, an exchange into the Fund followed by an exchange out of the Fund is treated as a single round trip. Also for these purposes, where known, accounts under common ownership or control generally will be counted together. Accounts maintained or

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Your Account

managed by a common intermediary, such as an adviser, selling agent or trust department, generally will not be considered to be under common ownership or control.

Purchases, redemptions and exchanges made through the Columbia Funds' Automatic Investment Plan, Systematic Withdrawal Plan or similar automated plans are not subject to the two-round-trip limit. Purchases, redemptions and exchanges made by Columbia Thermostat Fund are also not subject to the two round-trip limit. The two-round-trip limit may be modified for, or may not be applied to, accounts held by certain retirement plans to conform to plan limits, considerations relating to the Employee Retirement Income Security Act of 1974 or regulations of the Department of Labor, and for certain asset allocation or wrap programs.

The practices and policies described above are intended to deter and curtail market timing in the Fund. However, there can be no assurance that these policies, individually or collectively, will be totally effective in this regard because of various factors. In particular, a substantial portion of purchase, redemption and exchange orders are received through omnibus accounts. Omnibus accounts, in which shares are held in the name of an intermediary on behalf of multiple beneficial owners, are a common form of holding shares among financial intermediaries and retirement plans. The Fund typically is not able to identify trading by a particular beneficial owner through an omnibus account, which may make it difficult or impossible to determine if a particular account is engaged in market timing. Consequently, there is the risk that the Fund may not be able to identify, deter or curtail certain market timing that occurs in the Fund, which may result in certain shareholders being able to market time the Fund while the shareholders in the Fund bear the burden of such activities.

Certain financial intermediaries, including certain retirement plan service providers whose clients include, among others, various retirement plans sponsored by Bank of America and its affiliates for the benefit of its employees (the "Bank of America retirement plan service providers"), have different policies regarding monitoring and restricting market timing in the underlying beneficial owner accounts that they maintain through an omnibus account that may be more or less restrictive than the Fund practices discussed above. In particular, the Bank of America retirement plan service providers permit the reinstatement of future purchase orders for shares of the Fund following various suspension periods. If an intermediary does not enforce the Fund's policy, the intermediary must either provide data transparency to Columbia Management or Columbia Management must determine that the intermediary's policy taken in its entirety provid es protections to Fund shareholders that are generally commensurate with the Fund's policy.

The Fund seeks to act in a manner that it believes is consistent with the best interests of Fund shareholders in making any judgments regarding market timing. Neither the Fund nor its agents shall be held liable for any loss resulting from rejected purchase orders or exchanges.

The Fund will assess, subject to limited exceptions, a 2.00% redemption fee on the proceeds of Fund shares that are redeemed (either by selling shares or exchanging into another Columbia fund) within 60 days of their purchase. The redemption fee is paid to the Fund.

The redemption fee is imposed on Fund shares redeemed (including redemptions by exchange) within 60 days of purchase. In determining which shares are being redeemed, the Fund generally applies a first-in, first-out approach. For Fund shares acquired by exchange, the holding period prior to the exchange will not be considered in determining whether to assess the redemption fee.

The redemption fee will not be imposed if you qualify for a waiver and the Fund has received proper notification, unless the waiver is automatic as noted below. The Fund will redeem any shares that are eligible for a waiver first.

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Your Account

A Fund shareholder won't pay an otherwise applicable redemption fee on any of the following transactions:

•  shares sold following the death or disability (as defined in the tax code) of the shareholder, including a registered joint owner

•  shares sold by or distributions from participant directed retirement plans, such as 401(k), 403(b), 457, Keogh, profit sharing, and money purchase pension accounts, where the Fund does not have access to information about the individual participant account activity, except where the Fund has received an indication that the plan administrator is able to assess the redemption fee to the appropriate accounts (automatic)

•  shares sold by certain investment funds, including those that Columbia Management Advisors, LLC or its affiliates may manage (automatic)

•  shares sold as part of an automatic rebalancing within an asset allocation program or by certain wrap programs where the program sponsor has provided assurances reasonably satisfactory to the Fund that the program is not designed to be a vehicle for market timing

•  shares sold by accounts maintained by a financial institution or intermediary where the Fund has received information reasonably satisfactory to the Fund indicating that the financial institution or intermediary is unable for administrative reasons to assess the redemption fee to underlying shareholders

•  shares sold by an account which has demonstrated a hardship, such as a medical emergency, as determined in the absolute discretion of the Fund

•  shares that were purchased by reinvested dividends (automatic)

•  shares that are redeemed or exchanged through Columbia funds' Systematic Withdrawal Plan or similar affiliated or unaffiliated automated plans

•  the following retirement plan distributions:

•  lump-sum or other distributions from a qualified corporate or self-employed retirement plan following retirement (or following attainment of age 59¹/₂ in the case of a "key employee" of a "top heavy" plan)

•  distributions from an individual retirement account (IRA) or Custodial Account under Section 403(b)(7) of the tax code, following attainment of age 59¹/₂

The Fund also has the discretion to waive the 2.00% redemption fee if the Fund is in jeopardy of failing the 90% income test or losing its registered investment company qualification for tax purposes.

As described above, certain intermediaries do not assess redemption fees to certain categories of redemptions that do not present significant market timing concerns (such as automatic withdrawal plan redemptions). In these situations, the Fund's ability to assess redemption fees is generally limited by the intermediary's policies and, accordingly, no redemption fees will be assessed on such redemptions.

15

Your Account

FINANCIAL INTERMEDIARY PAYMENTS

The Fund's distributor, investment adviser or their affiliates may make payments, from their own resources, to certain financial intermediaries, including other Bank of America affiliates, for marketing support services. For purposes of this section the term "financial intermediary" includes any broker, dealer, bank, bank trust department, registered investment adviser, financial planner, retirement plan or other third-party administrator and any other institution having a selling, services or any similar agreement with the Fund's distributor, investment adviser or one of their affiliates. These payments are generally based upon one or more of the following factors: average net assets of the mutual funds distributed by the Fund's distributor attributable to that financial intermediary, gross sales of the mutual funds distributed by the Fund's distributor attributable to that financial intermediary, reimbursement of ticket charge s (fees that a financial intermediary firm charges its representatives for effecting transactions in fund shares) or a negotiated lump sum payment.

While the financial arrangements may vary for each financial intermediary, the support payments to any one financial intermediary are generally expected to be between 0.05% and 0.45% on an annual basis for payments based on average net assets of the Fund attributable to the financial intermediary, and between 0.10% and 0.25% on an annual basis for firms receiving a payment based on gross sales of the Fund attributable to the financial intermediary. The Fund's distributor, investment adviser or their affiliates may make payments in materially larger amounts or on a basis materially different from those described above when dealing with other affiliates of Bank of America. Such increased payments to the other Bank of America affiliate may enable the other Bank of America affiliate to offset credits that it may provide to its customers in order to avoid having such customers pay fees to multiple Bank of America entities in connecti on with the customer's investment in the Fund.

Payments also may be made to certain financial intermediaries, including other Bank of America affiliates, that provide investor services to retirement plans and other investment programs to compensate financial intermediaries for services they provide to such programs, including, but not limited to, sub-accounting, sub-transfer agency, similar shareholder or participant recordkeeping, shareholder or participant reporting, or shareholder or participant transaction processing. These payments for investor servicing support vary by financial intermediary but generally are not expected, with certain limited exceptions, to exceed 0.45% of the total Fund assets for Class Z shares in the program on an annual basis.

The Trust's Board of Trustees has authorized the Fund to pay to any intermediary up to 0.05% of the average aggregate value of Fund shares in the intermediary's program on an annual basis for providing investor services. Charges of an intermediary in excess of that paid by the Fund will be borne by the Fund's distributor or its affiliates.

The Fund's distributor, investment adviser or their affiliates may make other payments or allow promotional incentives to financial intermediaries to the extent permitted by the rules of the Securities and Exchange Commission, the National Association of Securities Dealers and by other applicable laws and regulations.

Amounts paid by the Fund's distributor, investment adviser or their affiliates are paid out of the distributor's, investment adviser's or their affiliates' own resources and do not increase the amount paid by you or the Fund. You can find further details about the payments made by the Fund's distributor, investment adviser or their affiliates and the services provided by financial intermediaries as well as a list of the financial intermediaries to which the Fund's distributor, investment adviser or their affiliates have agreed to make marketing support payments in the Fund's SAI, which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611. Your financial intermediary

16

Your Account

may charge you fees or commissions in addition to those disclosed in this prospectus. You can ask your financial intermediary for information about any payments it receives from the Fund's distributor, investment adviser and their affiliates and any services your financial intermediary provides, as well as fees and/or commissions it charges. In addition, depending on the financial arrangement in place at any particular time, a financial intermediary and its financial consultants also may have a financial incentive for recommending a particular fund or share class over others. You should consult with your financial adviser and review carefully any disclosure by the financial intermediary as to compensation received by your financial adviser.

OTHER INFORMATION ABOUT YOUR ACCOUNT

How the Fund's Share Price is Determined The Fund's Class Z share price is based on its net asset value. The net asset value is determined at the close of regular trading on the NYSE, usually 4:00 p.m. Eastern time, on each business day that the NYSE is open for trading (typically Monday through Friday). Net asset value is not determined on days on which the NYSE is closed for trading.

When you request a transaction, it will be processed at the net asset value per share next determined after your request is received in "good form" by the distributor. In most cases, in order to receive that day's price, the Fund must receive your order before that day's transactions are processed. If you request a transaction through your financial advisor, your financial advisor must receive your order by the close of trading on the NYSE to receive that day's price.

The Fund determines its net asset value for its Class Z shares by dividing total net assets attributable to Class Z shares by the number of outstanding Class Z shares. In determining the net asset value, the Fund must determine the value of each security in its portfolio at the close of each trading day. Because the Fund holds securities that are traded on foreign exchanges, the value of the Fund's securities may change on days when shareholders will not be able to buy or sell Fund shares. This will affect the Fund's net asset value on the day it is next determined. Securities for which market quotations are available are valued each day at the current market value. However, where market quotations are unavailable, or when the adviser believes that subsequent events have made them unreliable, the Fund may use other data to determine the fair value of the securities.

The Fund has retained an independent statistical fair value pricing service to assist in the fair valuation process for securities principally traded in a foreign market in order to adjust for possible changes in value that may occur between the close of the foreign exchange and the time at which Fund shares are priced. The use of an independent fair value pricing service is intended to and may decrease the opportunities for time zone arbitrage transactions. There can be no assurance that the use of an independent fair value pricing service will successfully decrease arbitrage opportunities. If a security is valued at a "fair value," that value may be different from the last quoted market price for the security.

You can find the daily prices of some share classes for the Fund in most major daily newspapers under the heading of "Columbia." You can find daily prices for all share classes by visiting www.columbiafunds.com.

Share Certificates Share certificates are not available for Class Z shares.

17

Your Account

Dividends, Distributions, and Taxes The Fund has the potential to make the following distributions:

Types of Distributions

Dividends	Represents interest and dividends earned from securities held by the Fund, net of expenses incurred by the Fund.
Capital gains	Represents net long-term capital gains on sales of securities held for more than one year and net short-term capital gains, which are gains on sales of securities held for a one-year period or less.

Distribution Options The Fund distributes any dividends in June and December and any capital gains (including short-term capital gains) at least annually. You can choose one of the options listed in the table below for these distributions when you open your account. To change your distribution option call 1-800-345-6611.

If you do not indicate on your application or at the time your account is established your preference for handling distributions, the Fund will automatically reinvest all distributions in additional shares of the Fund.

UNDERSTANDING FUND DISTRIBUTIONS

The Fund may earn income from the securities it holds. The Fund also may realize capital gains or losses on sales of its securities. The Fund intends to distribute substantially all of its net investment income and capital gains to shareholders each year. As a shareholder, you are entitled to a portion of the Fund's income and capital gains based on the number of shares you own at the time these distributions are declared.

Distribution Options

Reinvest all distributions in additional shares of the Fund

Reinvest all distributions in shares of another fund

Receive dividends in cash (see options below) and reinvest capital gains

Receive all distributions in cash (with one of the following options):

•  send the check to your address of record

•  send the check to a third-party address

•  transfer the money to your bank via electronic funds transfer

Distributions of $10 or less will automatically be reinvested in additional Fund shares. If you elect to receive distributions by check and the check is returned as undeliverable, all subsequent distributions will be reinvested in additional shares of the Fund.

Taxes Unless you are an entity exempt from income taxes or invest under a retirement account, regardless of whether you receive your distributions in cash or reinvest them in additional Fund shares, all Fund distributions are subject to federal income tax. Depending on where you live, distributions also may be subject to state and local income taxes.

The Fund intends to elect to be treated and to qualify each year as a regulated investment company. A regulated investment company is not subject to tax at the corporate level on income and gains from investments that are distributed to shareholders in accordance with applicable law. However, the Fund's failure to qualify as a regulated investment company could result in corporate level taxation, and consequently, a reduction in income available for distribution to shareholders.

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Your Account

In general, any distributions of dividends, interest and short-term capital gains (determined by how long the Fund held the investments that generated them) are taxable as ordinary income, unless such dividends are "qualified dividend income" (as defined in the Internal Revenue Code) eligible for a reduced rate of tax. Properly designated distributions of long-term capital gains (determined by how long the Fund held the investments that generated them) are generally taxable as such, regardless of how long you have held your Fund shares. You will be provided with information each year regarding the amount of ordinary income and capital gains distributed to you for the previous year and any portion of your distribution which is exempt from state and local taxes. The Fund's investments in foreign securities may be subject to foreign withholding taxes. You may be entitled to claim a credit or deduction with respect to foreign taxes. Long-term capital gain rates have been reduced — in general, to 15% with lower rates applying to taxpayers in the 10% and 15% rate brackets — for taxable years beginning before January 1, 2011. Distributions are taxable to you even if they are paid from income or gains earned by the Fund before you made your investment (and thus were included in the price you paid). Your investment in the Fund may have additional personal tax implications. Please consult your tax advisor about foreign, federal, state, local or other applicable tax laws.

In addition to the dividends and capital gains distributions made by the Fund, you may realize a capital gain or loss when selling or exchanging shares of the Fund. Such transactions also may be subject to federal, state and local income tax.

Foreign Income Taxes The Fund may receive investment income from sources within foreign countries, and that income may be subject to foreign income taxes at the source. If the Fund pays non-refundable taxes to foreign governments during the year, the taxes will reduce the Fund's dividends but will still be included in your taxable income. You may be able to claim a credit or deduction on your tax return for your share of foreign taxes paid by the Fund.

Board of Trustees

The Fund is governed by its Board of Trustees. More than 75% of the Fund's Trustees are independent, meaning that they have no affiliation with the adviser or the Funds, apart from their positions as Trustees and the personal investments they may have made as private individuals.

The independent Trustees bring backgrounds in business and the professions and academia to their task of working with the Funds' officers to establish the policies and oversee the activities of the Funds. Among the Trustees' responsibilities are selecting the investment adviser for the Funds; negotiating the advisory agreements; reviewing other contracts; approving investment policies; monitoring Fund operations, performance, and costs; and nominating or selecting new Trustees.

Each Trustee serves until his or her retirement, resignation, death or removal; or otherwise as specified in the Trust's organizational documents. It is expected that every five years the Trustees will call a meeting of shareholders to elect Trustees. A Trustee must retire at the end of the year in which he or she attains the age of 75. Any Trustee may be removed at a shareholders' meeting by a vote representing two-thirds of the net asset value of all shares of the Funds of the Trust. The mailing address for the Trustees and officers is 227W.Monroe, Suite 3000, Chicago, Illinois 60606.

For more detailed information on the Board of Trustees, please refer to the SAI.

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Managing the Fund

Managing the Fund

INVESTMENT ADVISER

Columbia Wanger Asset Management, L.P. (CWAM), located at 227 West Monroe Street, Suite 3000, Chicago, Illinois 60606, is the Fund's investment adviser and is responsible for the Fund's management, subject to the oversight of the Fund's Board of Trustees. CWAM and its predecessor have managed mutual funds, including the Fund, since 1992. In its duties as investment adviser, CWAM runs the Fund's day-to-day business, including making investment decisions and placing all orders for the purchase and sale of the Fund's portfolio securities.

CWAM was previously named Liberty Wanger Asset Management, L.P., and its predecessor was named Wanger Asset Management, L.P. (WAM). CWAM is a wholly owned subsidiary of Columbia Management Group, LLC, which in turn is an indirect wholly owned subsidiary of Bank of America Corporation. As of December 31, 2006, CWAM managed more than $32.9 billion in assets.

CWAM's advisory fee for managing the Fund in 2006 was 0.77% of the Fund's average daily net assets. CWAM also received an administrative fee from the Fund in 2006 of 0.04% of the Fund's average daily net assets. A discussion of the factors considered by the Fund's Board of Trustees in approving the Fund's investment advisory contract is included in the Fund's annual report to shareholders for the period ended December 31, 2006.

PORTFOLIO MANAGERS

CWAM uses a team to assist the lead portfolio managers in managing the Fund. Team members share responsibility for providing ideas, information and knowledge in managing the Fund, and each team member has one or more particular areas of expertise. Portfolio managers make strategic decisions and monitor and supervise individual transactions. While certain analysts recommend transactions for approval by the portfolio managers, more seasoned analysts are authorized to buy and sell securities for the Fund within the guidelines set by portfolio managers.

P. Zachary EganCo-portfolio manager
P. Zachary Egan is a vice president of the Trust and co-portfolio manager of Columbia Acorn International since May 2003. He has been CWAM's director of international research since December 2004. He has been a member of the international team since 1999.

Louis J. MendesCo-portfolio manager
Louis J. Mendes is a vice president of the Trust and co-portfolio manager of Columbia Acorn International since May 2003. He has been a member of the international team at CWAM since 2001. Mr. Mendes also is a vice president of Wanger Advisors Trust, and a co-portfolio manager of Wanger International Small Cap, an international mutual fund underlying variable insurance products.

The Statement of Additional Information provides additional information about the portfolio managers' compensation, other accounts managed and ownership of securities in the Fund.

20

Managing the Fund

LEGAL PROCEEDINGS

The Trust, CWAM and the trustees of the Trust (collectively, the "Columbia defendants") are named as defendants in class and derivative complaints, which were consolidated in a Multi-District Action in the federal district court for the District of Maryland on February 20, 2004 (the "MDL Action"). These lawsuits contend that defendants permitted certain investors to market time their trades in certain Columbia Acorn Funds. The MDL Action is ongoing All claims against the Trust and its independent trustees have been dismissed; however, the interested trustees of the Trust are still parties to the MDL Action.

On March 21, 2005, a class action complaint was filed against the Trust in the Superior Court of the Commonwealth of Massachusetts seeking to rescind the contingent deferred sales charges assessed upon redemption of Class B shares of Columbia Acorn Funds due to the alleged market timing by certain shareholders of the Columbia Acorn Funds. In addition to the rescission of sales charges, plaintiffs seek recovery of actual damages, attorneys' fees and costs. The case has been transferred to the MDL Action in the federal district court of Maryland.

The Trust and CWAM are also defendants in a class action lawsuit, filed on November 13, 2003 in the Circuit Court of the Third Judicial Circuit, Madison County, Illinois, that alleges, in summary, that the Trust and CWAM exposed shareholders of Columbia Acorn International to trading by market timers by allegedly (a) failing to properly evaluate daily whether a significant event affecting the value of the fund's securities had occurred after foreign markets had closed but before the calculation of the fund's net asset value; (b) failing to implement the fund's portfolio valuation and share pricing policies and procedures; and (c) failing to know and implement applicable rules and regulations concerning the calculation of net asset value ("Fair Valuation Lawsuit"). On April 5, 2005, the United States Court of Appeals for the Seventh Circuit ruled that the plaintiffs' state law claims were preempted under federal law resulting in the dismissal of plaintiffs' complaint. Plaintiffs appealed the Seventh Circuit's ruling to the United States Supreme Court. On June 15, 2006, the Supreme Court reversed the Seventh Circuit's ruling on jurisdictional grounds, and the case ultimately was remanded to the state court.

On April 4, 2006, the plaintiffs and the Columbia defendants named in the MDL Action executed an agreement in principle intended to fully resolve all of the lawsuits consolidated in the MDL Action as well as the Fair Valuation Lawsuit. The court entered a stay after the parties executed the agreement in principle. The settlement is subject to court approval.

In 2004, CWAM and the trustees of the Columbia Acorn Trust were named as defendants in certain purported shareholder class and derivative actions making claims, including claims under the Investment Company and the Investment Advisers Acts of 1940 and state law. Certain Columbia Acorn Funds were named as nominal defendants. The suits allege, inter alia, that the fees and expenses paid by the funds are excessive and that the funds' advisers and their affiliates inappropriately used fund assets to distribute the funds and for other improper purposes. On March 2, 2005, the actions were consolidated in the Massachusetts federal court as In re Columbia Entities Litigation. The plaintiffs filed a consolidated amended complaint on June 9, 2005. On November 30, 2005, the judge dismissed all claims by plaintiffs and entered final judgment in favor of the defendants. The plaintiffs appealed to the United States Court of Appeals for the First Circuit on December 30, 2005. A stipulation and settlement agreement dated January 19, 2007 was filed in the First Circuit on February 14, 2007, with a joint stipulation of dismissal and motion for remand to obtain district court approval of the settlement. The joint

21

motion was granted and the appeal was dismissed. On March 6, 2007, the case was remanded to the District Court, where the parties will seek court approval of the settlement. The terms of the proposed settlement, if approved, will require payments by the funds' adviser and/or its affiliates, including payment of plaintiffs' attorneys' fees and notice to class members. In the event that the settlement is not approved, the plaintiffs may elect to go forward with their appeal and no opinion is expressed regarding the likely outcome or financial impact of such an appeal on any fund.

On or about January 11, 2005, a putative class action lawsuit was filed in federal district court in Massachusetts against the Trust and its trustees, along with Columbia Management Advisors, LLC, the sub-administrator of the Wanger Advisors Funds and the Columbia Acorn Funds. The plaintiffs allege that the defendants failed to submit Proof of Claims in connection with settlements of securities class action lawsuits filed against companies in which the Columbia Acorn Funds held positions. The complaint seeks compensatory and punitive damages, and the disgorgement of all fees paid to Columbia Management Advisors, LLC. Plaintiffs have voluntarily dismissed the Trust and its independent trustees.

The Trust and CWAM intend to defend these suits vigorously.

As a result of these matters or any adverse publicity or other developments resulting from them, there may be increased redemptions or reduced sales of Fund shares, which could increase transaction costs or operating expenses, or have other adverse consequences for the Fund.

However, based on currently available information, the Trust believes that the likelihood that these lawsuits will have a material adverse impact on any fund is remote, and CWAM believes that the lawsuits are not likely to materially affect its ability to provide investment management services to the Fund.

Other Investment Strategies and Risks

The Fund's principal investment strategies and associated risks are described under "The Fund — Principal Investment Strategies" and "The Fund — Principal Investment Risks." This section describes other investments the Fund may make and the risks associated with them. In seeking to achieve its investment goal, the Fund may invest in various types of securities and engage in various investment techniques which are not the principal focus of the Fund and therefore are not described in this prospectus. These types of securities and investment practices and their associated risks are identified and discussed in the Fund's SAI, which you may obtain free of charge (see back cover). The adviser may elect not to buy any of these securities or use any of these techniques. The Fund may not always achieve its investment goal. Except as otherwise noted, approval by the Fund's shareholders is not required to modify or change the Fu nd's investment strategies.

THE INFORMATION EDGE

The Fund generally invests in entrepreneurially managed smaller- and mid-sized non-U.S. companies that it believes are not as well known by financial analysts and whose position in a niche creates the opportunity for superior earnings-growth potential. CWAM may identify what it believes are important economic, social or

22

Other Investment Strategies and Risks

technological trends (for example, the growth of outsourcing as a business strategy, or the productivity gains from the increasing use of technology) and try to identify companies it thinks will benefit from those trends.

In making investments for the Fund, CWAM relies primarily on independent, internally generated research to uncover companies that may be less well known than the more popular names. To find these companies, CWAM compares growth potential, financial strength and fundamental value among companies.

Growth Potential	Financial Strength	Fundamental Value
• superior technology • innovative marketing • managerial skill • market niche • good earnings prospects • strong demand for product	• low debt • adequate working capital • conservative accounting practices • adequate profit margin	• reasonable stock price relative to growth potential and financial strength • valuable assets
The realization of this growth potential would likely produce superior performance that is sustainable over time.	A strong balance sheet gives management greater flexibility to pursue strategic objectives and is important to maintaining a competitive advantage.	Once CWAM uncovers an attractive company, it identifies a price that it believes would also make the stock a good value.

LONG-TERM INVESTING

CWAM's analysts continually screen companies and make contact with more than 1,000 companies around the globe each year. To accomplish this, CWAM analysts often talk directly to top management, vendors, suppliers and competitors.

In managing the Fund, CWAM tries to maintain lower taxes and transaction costs by investing with a long-term time horizon (at least two to five years). Occasionally, however, securities purchased on a long-term basis may be sold within 12 months after purchase due to changes in the circumstances of a particular company or industry, or changes in general market or economic conditions.

DERIVATIVE STRATEGIES

The Fund may enter into a number of derivative strategies, including those that employ futures, options, straddles or similar transactions, to gain or reduce exposure to particular securities or markets. These strategies, commonly referred to as derivatives, involve the use of financial instruments whose values depend on, or are derived from, the value of an underlying security, index or currency. The Fund may use these strategies to adjust the Fund's sensitivity to changes in interest rates, or for other hedging purposes (i.e., attempting to offset a potential loss in one position by establishing an interest in an opposite position). Derivative strategies involve the risk that they may exaggerate a loss, potentially losing more money than the actual cost of the underlying security, or limit a potential gain. Also, with some derivative strategies there is a risk that the other party to the transaction may fail to honor its contr act terms, causing a loss to the Fund or that the Fund may not be able to find a suitable derivative transaction counterparty, and thus may be unable to invest in derivatives altogether.

23

Other Investment Strategies and Risks

TEMPORARY DEFENSIVE STRATEGIES

At times, CWAM may determine that adverse market conditions make it desirable to temporarily suspend the Fund's normal investment activities. During such times, the Fund may, but is not required to, invest in cash or high-quality, short-term debt securities, without limit. Taking a temporary defensive position may prevent the Fund from achieving its investment goal.

24

Financial Highlights

The financial highlights table is intended to help you understand the Fund's Class Z financial performance. Information is shown for the Fund's last five fiscal years, which run from January 1 to December 31. Certain information in the table reflects the financial results for a single Class Z share. The total returns in the table represent the return that you would have earned (or lost) on an investment in the Fund (assuming reinvestment of all dividends and distributions). This information has been derived from the Fund's financial statements, which have been audited for the years ended December 31, 2004, 2005 and 2006 by PricewaterhouseCoopers LLP, an independent registered public accounting firm, whose report, along with the Fund's financial statements, is included in the Fund's annual report. The information for the years ended December 31, 2002 and 2003 is included in the Fund's financial statements that have been audited b y another independent registered public accounting firm, whose report expressed an unqualified opinion on those financial statements and highlights. You can request a free annual report containing those financial statements by calling 1-800-345-6611.

Columbia Acorn International

	Year ended December 31,
	2006			2005			2004			2003			2002
	Class Z			Class Z			Class Z			Class Z			Class Z
Net Asset Value — Beginning of Period ($)		33.44			29.03			22.66			15.40			18.47
Income from Investment Operations ($)
Net investment income(a)		0.35			0.34			0.25			0.21			0.14
Net realized and unrealized gain (loss)		10.94			5.87			6.37			7.13			(3.10	)
Total Income from Investment Operations		11.29			6.21			6.62			7.34			(2.96	)
Less Distributions Declared to Shareholders ($):
From net investment income		(0.51	)		(0.72	)		(0.25	)		(0.08	)		(0.11	)
From net realized gains		(3.91	)		(1.08	)		—			—			—
Total Distributions Declared to Shareholders		(4.42	)		(1.80	)		(0.25	)		(0.08	)		(0.11	)
Redemption Fees
Redemption fees added to paid in capital		0.00	(a)(b)		0.00	(a)(b)		0.00	(a)(b)		—			—
Net Asset Value — End of Period ($)		40.31			33.44			29.03			22.66			15.40
Total return (%)(c)		34.53	(d)		21.81	(d)		29.47	(d)		47.80			(16.10	)
Ratios to Average Net Assets Supplemental Data (%):
Expenses(e)		0.94			0.99			1.08			1.05			1.06
Net investment income(e)		0.92			1.09			1.01			1.19			0.80
Waiver/reimbursement		0.01			0.02			0.02			—			—
Portfolio turnover rate (%)		31			27			40			40			52
Net assets, end of period (in millions) ($)		3,836			2,629			1,919			1,563			1,241

(a)  Per share data was calculated using average shares outstanding during the period.

(b)  Rounds to less than $0.01 per share.

(c)  Total return at net asset value assuming all distributions reinvested.

(d)  Had the investment adviser and/or transfer agent not waived and/or reimbursed a portion of expenses, total return would have
been reduced.

(e)  The benefits derived from custody fees paid indirectly had no impact.

25

Appendix

Hypothetical Investment and Expense Information

The Fund is required to disclose the following supplemental hypothetical investment information, which provides additional information about the effect of the expenses paid by the Fund, including investment advisory fees and other Fund costs, on the Fund's returns over a 10-year period. The table shows the estimated expenses that would be charged on a hypothetical investment of $10,000 in Class Z shares of the Fund assuming a 5% return each year, the cumulative return after fees and expenses, and the hypothetical year-end balance after fees and expenses. The table also assumes that all dividends and distributions are reinvested. The annual expense ratio used for the Fund, which is the same as that stated in the Annual Fund Operating Expenses table, is presented in the table, and is net of any contractual fee waivers or expense reimbursements for the period of the contractual commitment. Your actual costs may be higher or lower.< /font>

Columbia Acorn International — Class Z Shares

Maximum Sales Charge 0.00%					Initial Hypothetical Investment Amount $10,000.00						Assumed Rate of Return 5%
Year		Cumulative Return Before Fees & Expenses			Annual Expense Ratio			Cumulative Return After Fees & Expenses			Hypothetical Year-End Balance After Fees & Expenses		Annual Fees & Expenses (1)
	1		5.00	%		0.94	%		4.06	%	$	10,406.00	$	95.91
	2		10.25	%		0.94	%		8.28	%	$	10,828.48	$	99.80
	3		15.76	%		0.94	%		12.68	%	$	11,268.12	$	103.85
	4		21.55	%		0.94	%		17.26	%	$	11,725.61	$	108.07
	5		27.63	%		0.94	%		22.02	%	$	12,201.67	$	112.46
	6		34.01	%		0.94	%		26.97	%	$	12,697.05	$	117.02
	7		40.71	%		0.94	%		32.13	%	$	13,212.55	$	121.78
	8		47.75	%		0.94	%		37.49	%	$	13,748.98	$	126.72
	9		55.13	%		0.94	%		43.07	%	$	14,307.19	$	131.86
	10		62.89	%		0.94	%		48.88	%	$	14,888.06	$	137.22
Total Gain After Fees and Expenses											$	4,888.06
Total Annual Fees and Expenses													$	1,154.69

(1)  Annual Fees and Expenses are calculated based on the average between the beginning and ending balance for each year.
All information is calculated on an annual compounding basis.

26

Notes

27

FOR MORE INFORMATION

Additional information about the Fund's investments is available in the Fund's semiannual and annual reports to shareholders. The annual report contains a discussion of the market conditions and investment strategies that significantly affected the Fund's performance during its last fiscal year.

You may wish to read the SAI for more information on the Fund and the securities in which it invests. The SAI is incorporated into this prospectus by reference, which means that it is considered to be part of this prospectus.

You can get free copies of annual and semiannual reports and the SAI, request other information and discuss your questions about the Fund by visiting www.columbiafunds.com or by writing or calling the Fund's transfer agent at:

Columbia Management Services, Inc.
P.O. Box 8081
Boston, MA 02266-8081
1-800-345-6611

Text-only versions of all Fund documents can be viewed online or downloaded from the EDGAR database on the Securities and Exchange Commission internet site at www.sec.gov.

You can review and copy information about the Fund, including the SAI, by visiting the following location, and you can obtain copies upon payment of a duplicating fee, by electronic request at the e-mail address publicinfo@sec.gov or by writing the:

Public Reference Room
Securities and Exchange Commission
Washington, DC 20549-0102

Information on the operation of the Public Reference Room may be obtained by calling 1-202-942-8090.

Investment Company Act file number:
Columbia Acorn Trust: 811-01829
•  Columbia Acorn International

©2007 Columbia Management Distributors, Inc.
One Financial Center, Boston, MA 02111-2621
800.426.3750 www.columbiafunds.com

INT-36/130112-0507

Columbia^SM

Acorn USA^®  Prospectus, May 1, 2007

Class A, B and C Shares

Advised by Columbia Wanger Asset Management, L.P.

TABLE OF CONTENTS

THE FUND	2
Investment Goal	2
Principal Investment Strategies	2
Principal Investment Risks	2
Portfolio Holdings Disclosure	3
Performance History	4
Commissions and Other Expenses	6
YOUR ACCOUNT	8
Choosing a Share Class	8
How to Buy Shares	9
Investment Minimums	9
Sales Charges (Commissions)	10
How to Exchange Shares	16
How to Sell Shares	16
Fund Policy on Trading of Fund Shares	17
Other Information About Your Account	19
BOARD OF TRUSTEES	21
MANAGING THE FUND	22
Investment Adviser	22
Portfolio Manager	22
Legal Proceedings	22
OTHER INVESTMENT STRATEGIES AND RISKS	24
The Information Edge	24
Long-Term Investing	25
Derivative Strategies	25
Temporary Defensive Strategies	25
FINANCIAL HIGHLIGHTS	26
APPENDIX	29

Although these securities have been registered with the Securities and Exchange Commission, the Commission has not approved or disapproved any shares offered in this prospectus or determined whether this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Acorn USA^® is a trademark owned and registered by Columbia Acorn Trust, Columbia, Columbia Management^® and Columbia Management Services, Inc. are service marks owned and/or registered by Bank of America

The Fund

INVESTMENT GOAL

Columbia Acorn USA (Acorn USA^®) seeks to provide long-term growth of capital.

PRINCIPAL INVESTMENT STRATEGIES

Acorn USA invests generally in stocks of small- and medium-sized U.S. companies. The Fund generally invests in the stocks of U.S. companies with capitalizations of less than $5 billion at the time of initial purchase. As long as a stock continues to meet the Fund's other investment criteria, the Fund may choose to hold a stock even if the issuing company's capitalization grows beyond a $5 billion capitalization.

Acorn USA believes that these smaller companies, which are not as well known by financial analysts, may offer higher return potential than the stocks of larger companies.

Acorn USA typically looks for companies with:

•  A strong business franchise that offers growth potential.

•  Products and services that give the company a competitive advantage.

•  A stock price the Fund's investment adviser believes is reasonable relative to the assets and earning power of the company.

Acorn USA generally invests substantially all of its assets in U.S. companies and, under normal circumstances, will invest at least 80% of its net assets (plus any borrowings for investment purposes) in U.S. companies.

Additional strategies that are not principal investment strategies and the risks associated with them are described later in this prospectus under "Other Investment Strategies and Risks."

PRINCIPAL INVESTMENT RISKS

The principal risks of investing in the Fund are described below. There are many circumstances (including additional risks that are not described here) which could prevent the Fund from achieving its investment goal. You may lose money by investing in the Fund.

Management risk means that the adviser's investment decisions might produce losses or cause the Fund to underperform when compared to other funds with a similar investment goal. Market risk means that security prices in a market, sector or industry may fall, reducing the value of your investment. Because of management and market risk, there is no guarantee that the Fund will achieve its investment goal or perform favorably among comparable funds.

Since the Fund purchases equity securities, it is subject to equity risk. This is the risk that stock prices will fall over short or extended periods of time. Although the stock market historically has outperformed other asset classes over the long term, the stock market tends to move in cycles. Individual stock prices may fluctuate drastically from day-to-day and may underperform other asset classes over an extended period of time. Individual companies may report poor results or be negatively affected by industry and/or economic trends and developments. The prices of securities issued by such companies may suffer a decline in response. These price movements may result from factors affecting individual companies, industries or the securities market as a whole.

Because the Fund invest in stocks, the price of its shares — its net asset value (NAV) per share — fluctuates daily in response to changes in the market value of stocks.

2

The Fund

Sector risk is inherent in the Fund's investment strategy. Companies that are in different but closely related industries are sometimes described as being in the same broad economic sector. The values of stocks of different companies in a market sector may be similarly affected by particular economic or market events. Although the Fund does not intend to focus on any particular sector, at times the Fund may have a large portion of its assets invested in a particular sector.

Small- or mid-cap companies may be more susceptible to market downturns, and their prices could be more volatile than large-cap companies. These companies are more likely than larger companies to have limited product lines, operating histories, markets or financial resources. They may depend heavily on a small management team and may trade less frequently, may trade in smaller volumes and may fluctuate more sharply in price than stocks of larger companies. In addition, such companies may not be widely followed by the investment community, which can lower the demand for their stocks.

An investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PORTFOLIO HOLDINGS DISCLOSURE

A description of the Fund's policies and procedures with respect to the disclosure of its portfolio securities is available in the Fund's Statement of Additional Information (SAI), which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611.

The Fund posts its complete portfolio holdings as of month-end at www.columbiafunds.com approximately 30-40calendar days after such month-end. Additionally, the Fund discloses its top 15 month-end portfolio holdings at www.columbiafunds.com on or about 15 calendar days following such month-end.

Once posted, the above information will remain available on the website until at least the date on which the Fund files a Form N-CSR or FormN-Q for the period that includes the date as of which the information is current.

3

The Fund

PERFORMANCE HISTORY

The bar chart below shows the Fund's calendar-year total returns (before taxes) for its Class A shares, excluding sales charges. The performance table following the bar chart shows how the Fund's average annual total returns for Class A, B and C shares, including sales charges, compare with a broad measure of market performance for one year, five years and the life of the share class. The chart and table are intended to illustrate some of the risks of investing in the Fund by showing changes in the Fund's performance from year to year. All returns include the reinvestment of dividends and distributions. As with all mutual funds, past performance (before and after taxes) does not predict the Fund's future performance.

UNDERSTANDING PERFORMANCE

Calendar Year Total Returns show the Fund's Class A share performance for each complete calendar year since the Class commenced operations. Those returns include the effects of Fund expenses, but not the effects of sales charges paid directly by a shareholder. If sales charges were included, these returns would be lower.

Average Annual Total Returns are a measure of the Fund's average performance over the past one year, five years and the life of the share class. The table shows the returns of each share class and includes the effects of both Fund expenses and current sales charges. Class B share returns do not reflect Class A share returns after conversion of Class B shares to Class A shares — see the section "Your Account — Sales Charges (Commissions)."

The Fund's returns are compared to the Russell 2000^® Index (Russell 2000^®). The Russell 2000^® is a market-weighted index of the 2000 smallest companies of the 3000 largest U.S. companies based on market-capitalization. All third-party trademarks are the property of their owners. Unlike the Fund, an index is not an investment, does not incur fees, expenses or taxes, and is not professionally managed.

Calendar Year Total Returns (Class A)

For the periods shown in bar chart:
Best quarter: 2nd quarter 2003, +23.06%
Worst quarter: 3rd quarter 2002, -21.36%

4

The Fund

After-tax returns are calculated using the highest historical individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on each investor's own tax situation and may differ from those shown. After-tax returns may not be relevant to investors who hold Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Average Annual Total Returns — for periods ended December 31, 2006⁽¹⁾

Share Class	1 Year		5 Years		Life of the Share Class(2)
Class A (%)
Return Before Taxes		1.74		10.29		12.53
Return After Taxes on Distributions		1.42		10.04		12.29
Return After Taxes on Distributions and Sale of Fund Shares		1.56		8.96		11.04
Class B (%)
Return Before Taxes		2.29		10.60		12.88
Return After Taxes on Distributions		1.93		10.33		12.63
Return After Taxes on Distributions and Sale of Fund Shares		1.96		9.23		11.36
Class C (%)
Return Before Taxes		6.14		10.81		12.84
Return After Taxes on Distributions		5.78		10.55		12.59
Return After Taxes on Distributions and Sale of Fund Shares		4.47		9.43		11.32
Index
Russell 2000® (%)		18.37		11.39		9.67	(3)

(1)   Performance may reflect any voluntary waiver or reimbursement of Fund expenses by the investment adviser or its affiliates. Absent these waivers or reimbursement arrangements, performance results would have been lower.

(2)   The inception date for Class A, Class B and Class C shares is October 16, 2000.

(3)   Performance information is from October 16, 2000.

5

The Fund

COMMISSIONS AND OTHER EXPENSES

Expenses are one of several factors to consider before you invest in a mutual fund. The tables below describe the commissions and other expenses you may pay when you buy, hold and sell shares of the Fund.

UNDERSTANDING EXPENSES

Sales Charges (Commissions) are paid directly by shareholders to Columbia Management Distributors, Inc., the Fund's distributor, who compensates your financial advisor.

Annual Fund Operating Expenses are paid by the Fund. They include management and administration fees, 12b-1 fees and other expenses that generally include, but are not limited to, transfer agency, custody, and legal fees as well as costs related to state registration and printing of Fund documents. The specific fees and expenses that make up the Fund's other expenses will vary from time to time and may include fees or expenses not described here. The Fund will likely incur portfolio transaction costs that are in addition to the total annual fund operating expenses disclosed in the fee table. These transaction costs are made up of all costs that are associated with trading securities for the Fund's portfolio and include, but are not limited to, brokerage commissions and market spreads, as well as potential changes to the price of a security due to the Fund's efforts to purchase or sell it. While certain elements of transaction costs are readily identifiable and quantifiable, other elements that can make up a significant amount of the Fund's transaction costs are not. Higher transaction costs reduce the Fund's returns.

Shareholder Fees (commissions paid directly from your investment)

	Class A			Class B		Class C
Maximum sales charge (load) on purchases (%) (as a percentage of the offering price)		5.75		None		None
Maximum deferred sales charge (load) on redemptions (%) (as a percentage of the lesser of purchase price or redemption price)		1.00	(1)		5.00		1.00
Redemption fee (%) (as a percentage of amount redeemed, if applicable)	None(2)			None(2)		None(2)

(1)  This charge applies only to certain purchases of Class A shares bought without an initial sales charge that are sold within 12 months of purchase.

(2)  There is a $7.50 charge for wiring sale proceeds to your bank.

6

The Fund

Annual Fund Operating Expenses (deducted directly from Fund assets)

	Class A		Class B		Class C
Management fees(1) (%)		0.86		0.86		0.86
Distribution and service (12b-1) fees(2) (%)		0.25		0.75		1.00
Other expenses(3) (%)		0.19		0.28		0.23
Total annual fund operating expenses (%)		1.30		1.89		2.09

(1)  The fund pays an investment advisory fee of 0.86%. The Fund and its adviser have implemented a breakpoint schedule for the Fund's investment advisory fees. The investment advisory fee rates charged to the Fund will decline as Fund assets grow and will continue to be based on a percentage of the Fund's average daily assets. The annual fee schedule for the Fund is as follows: 0.94% for assets up to $200 million; 0.89% for assets in excess of $200 million and up to $500 million; 0.84% for assets in excess of $500 million and up to $2 billion; and 0.80% for assets in excess of $2 billion and up to $3 billion; and 0.70% for assets in excess of $3 billion. In addition to the management fee, the Fund and the other funds of Columbia Acorn Trust (the "Trust") pay the adviser an administrative fee based on the average daily aggregate net assets of the Trust at the following annual rates: 0.05% of net assets up to $8 billion ; 0.04% of the next $8 billion; and 0.03% of net assets in excess of $16 billion. Based on the Trust's average daily net assets as of December 31, 2006, the administrative fee would be at a rate of 0.04% and is included in "Other expenses."

(2)  The distribution and service (12b-1) fees for Class B shares have been restated to reflect a reduction of the distribution fee rate by 0.10%, effective August 1, 2006.

(3)  "Other expenses" have been restated to reflect contractual changes to the transfer agency fees paid by the Fund.

Example Expenses help you compare the cost of investing in the Fund to the cost of investing in other mutual funds. It uses the following hypothetical conditions:

•  $10,000 initial investment†

•  5% total return for each year

•  Fund operating expenses remain the same

•  Reinvestment of all dividends and distributions

•  Class B shares convert to Class A shares after eight years

†  For example only, since the minimum initial investment in the Fund is $75,000.

Example Expenses for a $10,000 investment (your actual costs may be higher or lower)

Class		1 Year		3 Years		5 Years		10 Years
Class A:		$	700	$	963	$	1,247	$	2,053
Class B:	did not sell your shares	$	192	$	594	$	1,021	$	2,058
	sold all your shares at
	the end of the period	$	692	$	894	$	1,221	$	2,058
Class C:	did not sell your shares	$	212	$	655	$	1,124	$	2,421
	sold all your shares at
	the end of the period	$	312	$	655	$	1,124	$	2,421

See the Appendix for additional hypothetical investment and expense information.

7

Your Account

CHOOSING A SHARE CLASS

The Fund offers three classes of shares in this prospectus — Class A, Class B and Class C. Each share class has its own commission and expense structure that affects the investment return of that class. Determining which share class is best for you depends on various factors, including the amount you are investing, how long you expect to hold your investment and your personal situation.

You should consult with your financial advisor before deciding which share class is most appropriate for you. The following considerations should be part of your assessment:

•  You will pay a commission if you buy Class A, B or C shares, either at the time of investment or redemption, or through ongoing distribution commission payments (Rule 12b-1 fees) made from your investment over time, or both.

•  Class A shares require an up-front commission payment, but pay lower ongoing Rule 12b-1 fees than Class B and Class C shares. Class B and Class C shares have no up-front commission paid by the shareholder but pay higher ongoing commissions (Rule 12b-1 fees), and a deferred commission is imposed on a redemption of Class B shares within six years after purchase, and a deferred commission is imposed on a redemption of Class C shares within one year of purchase. The differential between classes will vary depending on the actual investment return for any given period.

•  Class A shares can be more advantageous to an investor who intends to hold the shares for several years and invests an amount large enough to qualify for a reduced rate of initial sales commission, taking into account the commissions that investor may pay when redeeming shares of other classes. To project whether Class A shares might be more advantageous to you, you should consider, among other factors, the time period you intend to hold the shares, your initial sales commission and a comparison of the total annual expenses of Class A shares to the expenses of other share classes. Class A shares pay an ongoing annual commission (Rule 12b-1 fee) of up to 0.25% of the average value of the shares.

•  Class B shares are no longer offered to new investors. A Class B shareholder of the Fund whose account has a value of less than $50,000 (including for this purpose the combined value of all eligible accounts maintained by that shareholder that would be used to determine eligibility for reduced sales charges on Class A shares) may purchase additional Class B shares of the Fund to increase the account value up to a maximum of $49,999; any additional investment by the shareholder in that Fund will be invested in Class A shares of the Fund, without regard to the normal investment minimum for Class A shares, but will be subject to the applicable Class A shares up-front commission. Class B shares pay an ongoing annual commission (Rule 12b-1 fee) of up to 0.75% of the average value of the shares and automatically convert to Class A shares after eight years.

•  Class C shares are generally more advantageous to an investor who intends to hold shares for only a few years. Class C shares pay an ongoing annual commission (Rule 12b-1 fee) of up to 1.00% of the average value of the shares.

•  If you invest $1 million or more, you can purchase Class A shares but not Class C shares.

The Fund also offers an additional class of shares, Class Z shares, exclusively to certain institutional and other eligible investors. Class Z shares are made available through a separate prospectus provided to eligible institutional and other investors.

8

Your Account

HOW TO BUY SHARES

Your financial advisor can help you establish an appropriate investment portfolio, buy shares and monitor your investments. When the Fund receives your purchase request in "good form," your shares will be bought at the next calculated public offering price. "Good form" means that the Fund's transfer agent has all information and documentation it deems necessary to effect your order. For example "good form" may mean that you have properly placed your order with your financial advisor or the Fund's transfer agent has received your completed application, including all necessary signatures. The Fund reserves the right to refuse a purchase order for any reason, including if the Fund believes that doing so would be in the best interest of the Fund and its shareholders. The USA PATRIOT Act may require us to obtain certain personal information from you that we will use to verify your identity. If you do not provide the information, we m ay not be able to open your account. If we are unable to verify your customer information, we reserve the right to close your account or take such other steps as we deem reasonable.

INVESTMENT MINIMUMS

The investment minimum for initial investments (by purchase, exchange or certain transfers) of Class A, B and C shares is $75,000. The investment minimum is applied at the class level. For group retirement plans, the investment minimum is determined based on the amount of the plan's investment rather than that of its individual participants. The Fund may establish exclusions from the investment minimum from time to time that it deems appropriate and consistent with the interests of shareholders. Please see the SAI for details on these exclusions. The Fund reserves the right to change these investment minimums.

The Fund also reserves the right to refuse a purchase order for any reason, including if it believes that doing so would be in the best interest of the Fund and its shareholders. Finally, pursuant to the Trust's Agreement and Declaration of Trust, the Fund reserves the right to redeem your shares if your account falls below the minimum investment requirements.

Please see the SAI for more details on investment minimums.

Outlined below are the various options for buying shares:

Method	Instructions
Through your financial advisor	Your financial advisor can help you establish your account and buy Fund shares on your behalf. To receive the current trading day's price, your financial advisor must receive your request prior to the close of regular trading on the New York Stock Exchange (NYSE), usually 4:00 p.m. Eastern time. Your financial advisor may charge you fees for executing the purchase for you.
By check (new account)	For new accounts, send a completed application and check made payable to the Fund to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By check (existing account)	For existing accounts, fill out and return the additional investment stub included in your account statement, or send a letter of instruction including your name, the Fund's share class and account number with a check made payable to the Fund to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By exchange	You or your financial advisor may acquire Fund shares for your account by exchanging shares you own in a different fund distributed by Columbia Management Distributors, Inc. for shares of the same class (and, in some cases, certain other classes) of the Fund at no additional cost. An exchange to another fund may incur a sales charge if the original purchase was not assessed a sales charge. To exchange by telephone, call 1-800-422-3737. Please see "How to Exchange Shares" for more information.

9

Your Account

Method	Instructions
By wire	You may purchase Fund shares by wiring money from your bank account to your Fund account. To wire funds to your Fund account, call 1-800-422-3737 for wiring instructions.
By electronic funds transfer	You may purchase Fund shares by electronically transferring money from your bank account to your Fund account by calling 1-800-422-3737. An electronic funds transfer may take up to two business days to settle and must be considered in "good form." You must set up this feature prior to your telephone request. Be sure to complete the appropriate section of the application for this feature.
Automatic investment plan	You may make monthly or quarterly investments ($50 minimum) automatically from your bank account to your Fund account. You may select a pre-authorized amount to be sent via electronic funds transfer. Be sure to complete the appropriate section of the application for this feature.
Automated dollar cost averaging	You may purchase Fund shares for your account by exchanging $100 or more each month from another fund for shares of the same class of the Fund at no additional cost. Exchanges will continue so long as your fund balance is sufficient to complete the transfers. You may terminate your program or change the amount of the exchange (subject to the $100 minimum) by calling 1-800-345-6611. There may be an additional sales charge if exchanging from a money market fund. Be sure to complete the appropriate section of the account application for this feature.
By dividend diversification	You may automatically invest dividends distributed by another fund into the same class of shares (and, in some cases, certain other classes) of the Fund at no additional sales charge. There may be an additional sales charge if automatically investing dividends from a money market fund. To invest your dividends in the Fund, call 1-800-345-6611.
Through the internet	You may purchase Fund shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet purchases. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

SALES CHARGES (COMMISSIONS)

You may be subject to an initial sales charge when you purchase, or a contingent deferred sales charge (CDSC) when you sell, shares of the Fund. These sales charges are described below. In certain circumstances, the sales charge may be reduced or waived, as described below and in the SAI.

Rule 12b-1 Plan The Fund has adopted a plan under Rule 12b-1 under the Investment Company Act that permits it to pay its distributor ongoing sales and marketing fees (commissions) to support the sale and distribution of Class A, B and C shares and certain services provided to you by your financial advisor, and your financial advisor may receive all or a portion of those fees attributable to your shares. The annual fee, as a percentage of the value of the shares, is normally 0.25% for Class A, 0.75% for Class B and 1.00% for Class C shares. These fees are paid out of the assets of these share classes. Over time, these fees reduce the return on your investment. Class B shares automatically convert to Class A shares after eight years, eliminating a portion of the Rule 12b-1 fee thereafter.

Financial Intermediary Payments

The Fund's distributor, investment adviser or their affiliates will make payments, from their own resources, to certain financial intermediaries, including other Bank of America affiliates, for marketing support services. For purposes of this section the term "financial intermediary" includes any broker, dealer, bank, bank trust department, registered investment adviser, financial planner, retirement plan or other third-party administrator and any other institution having a selling, services or any similar agreement with the Fund's distributor, investment adviser or one of their affiliates. These payments are generally based upon one or more of the following factors: average net assets of the mutual funds distributed by the Fund's distributor attributable to that financial intermediary, gross sales of the mutual funds distributed by the Fund's distributor attributable to that financial intermediary, reimbursement of ticket charg es (fees that a financial intermediary firm charges its representatives for effecting transactions in fund shares) or a negotiated lump sum payment.

10

Your Account

While the financial arrangements may vary for each financial intermediary, the payments to any one financial intermediary are generally expected to be between 0.05% and 0.35% on an annual basis for payments based on average net assets of the Fund attributable to the financial intermediary, and between 0.10% and 0.25% on an annual basis for firms receiving a payment based on gross sales of the Fund attributable to the financial intermediary. The Fund's distributor, investment adviser or their affiliates may make payments in materially larger amounts or on a basis materially different from those described above when dealing with other affiliates of Bank of America. Such increased payments to the other Bank of America affiliate may enable the other Bank of America affiliate to offset credits that it may provide to its customers in order to avoid having such customers pay fees to multiple Bank of America entities in connection with the customer's investment in the Fund.

Payments also may be made to certain financial intermediaries, including other Bank of America affiliates, that provide investor services to retirement plans and other investment programs to compensate financial intermediaries for services they provide to such programs, including, but not limited to, sub-accounting, sub-transfer agency, similar shareholder or participant recordkeeping, shareholder or participant reporting, or shareholder or participant transaction processing. These payments for investor servicing support vary by financial intermediary but generally are not expected, with certain limited exceptions, to exceed 0.35% of the total Fund assets for Class A, B and C shares in the program on an annual basis.

The Trust's Board of Trustees has authorized the Fund to pay to any intermediary up to 0.05% of the average aggregate value of Fund shares in the intermediary's program on an annual basis for providing investor services. Charges of an intermediary in excess of that paid by the Fund will be borne by the Fund's distributor or its affiliates.

The Fund's distributor, investment adviser or their affiliates may make other payments or allow promotional incentives to financial intermediaries to the extent permitted by the rules of the Securities and Exchange Commission, the National Association of Securities Dealers and by other applicable laws and regulations.

Amounts paid by the Fund's distributor, investment adviser or their affiliates are paid out of the distributor's, investment adviser's or their affiliates' own resources and do not increase the amount paid by you or the Fund. You can find further details about the payments made by the Fund's distributor, investment adviser or their affiliates and the services provided by financial intermediaries as well as a list of the financial intermediaries to which the Fund's distributor, investment adviser or their affiliates have agreed to make marketing support payments in the Fund's SAI, which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611. Your financial intermediary may charge you fees or commissions in addition to those disclosed in this prospectus. You can ask y our financial intermediary for information about any payments it receives from the Fund's distributor, investment adviser and their affiliates and any services your financial intermediary provides, as well as fees and/or commissions it charges. In addition, depending on the financial arrangement in place at any particular time, a financial intermediary and its financial consultants also may have a financial incentive for recommending a particular fund or share class over others. You should consult with your financial adviser and review carefully any disclosure by the financial intermediary as to compensation received by your financial adviser.

Class A shares Your purchases of Class A shares are made at the public offering price for these shares. This price includes a sales charge that is based on the amount of your initial investment when you open your account. The sales charge you pay on an additional investment is based on the total amount of your purchase and the current value of your account. Shares you purchase with reinvested dividends or other distributions are not subject to a

11

Your Account

sales charge. A portion of the sales charge is paid as a commission to your financial advisor on your purchase of Class A shares. The amount of the sales charge differs depending on the amount you invest as shown in the table below.

Class A Sales Charges

	Sales Charge as % of:				% of offering price
Amount of purchase*	offering price		net amount invested		retained by your financial advisor
Less than $50,000**		5.75		6.10		5.00
$50,000 to less than $100,000**		4.50		4.71		3.75
$100,000 to less than $250,000		3.50		3.63		2.75
$250,000 to less than $500,000		2.50		2.56		2.00
$500,000 or more		2.00		2.04		1.75

*  Mutual fund wrap programs and group retirement plans that invest $75,000 or more in Class A shares of the Fund will not be subject to a sales charge.

**  Initial purchases of less than $75,000 are no longer accepted. However, for accounts opened prior to February 3, 2006, subsequent investments that do not meet the Fund's current investment minimum will be accepted.

In addition to the initial sales charge paid to your financial advisor and distributor, a 0.25% annual commission is paid to your financial advisor over the life of your investment out of your Fund assets as a 12b-1 fee.

The Fund's distributor may also pay additional compensation to financial advisors as an incentive for promoting the sale of shares of funds that it distributes.

Class A shares bought without initial sales charge in accounts aggregating $1 million to $50 million at the time of purchase are subject to a 1.00% CDSC if the shares are sold within 12 months of the time of purchase. Subsequent Class A share purchases that bring your account value above $1 million (but less than $50 million) are subject to a CDSC if redeemed within 12 months of the date of purchase. The 12-month period begins on the first day of the month in which the purchase was made. The CDSC does not apply to retirement purchasing shares through a fee-based program.

For Class A share purchases of $1 million or more, financial advisors receive a cumulative commission from the distributor as follows:

Purchases Over $1 Million

Amount purchased	Commission %
$1 million to less than $3 million		1.00
$3 million to less than $50 million		0.50
$50 million or more		0.25

For group retirement plans, financial advisors are eligible to receive a 1.00% commission from the distributor on purchases, including those in amounts of less than $1 million, that are coded as commission eligible trades. In determining the commission payable to a financial advisor in the above table, the breakpoint discount policies described in "Reduced Sales Charges (Commissions) for Larger Investments," on page 13, shall apply.

12

Your Account

UNDERSTANDING CONTINGENT DEFERRED SALES CHARGES (COMMISSIONS)

Certain investments in Class A, B and C shares are subject to a CDSC, a sales charge applied at the time you sell your shares. You will pay the CDSC only on shares you sell within a certain amount of time after purchase. The CDSC generally declines each year until there is no charge for selling shares. The CDSC is applied to the net asset value at the time of purchase or sale, whichever is lower. For purposes of calculating the CDSC, the start of the holding period is the first day of the month in which the purchase was made. Shares you purchase with reinvested dividends or other distributions are not subject to a CDSC. When you place an order to sell shares, the Fund will automatically sell first those shares not subject to a CDSC and then those you have held the longest.

Reduced Sales Charges (Commissions) for Larger Investments.

A.  What are the principal ways to obtain a breakpoint discount?

There are two principal ways you may pay a lower sales charge (often referred to as "breakpoint discounts") when purchasing Class A shares of the Fund and other funds in the Columbia family of funds.

Rights of Accumulation The value of eligible accounts maintained by you and each member of your immediate family may be combined with the value of your current purchase to reach a sales charge discount level (according to the chart on the previous page) and to obtain the lower sales charge for your current purchase. To calculate the combined value of the accounts, the Fund will use the shares' current public offering price.

Statement of Intent You also may pay a lower sales charge when purchasing Class A shares by signing a Statement of Intent. By doing so, you would be able to pay the lower sales charge on all purchases made under the Statement of Intent within 13 months. As described in the chart on the previous page, the first breakpoint discount will be applied when total purchases reach $50,000. If your Statement of Intent purchases are not completed within 13 months, you will be charged the applicable sales charge on the amount you had invested to that date. To calculate the total value of your Statement of Intent purchases, the Fund will use the historic cost (i.e. dollars invested) of the shares held in each eligible account. You must retain all records necessary to substantiate historic costs because the Fund and your financial intermediary may not maintain this information.

B.  What accounts are eligible for breakpoint discounts?

The types of eligible accounts that may be aggregated to obtain one or both of the breakpoint discounts described above include:

•  Individual accounts

•  Joint accounts

•  Certain IRA accounts

•  Certain trusts

•  UTMA/UGMA accounts

For the purposes of obtaining a breakpoint discount, members of your "immediate family" include your spouse, parent, stepparent, legal guardian, child, stepchild, father-in-law and mother-in-law. Eligible accounts include those registered in the name of your dealer or other financial intermediary through which you own Columbia

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fund shares. An account is not eligible to the extent it holds an institutional class of shares of a Columbia money market fund or Class R shares of any Columbia fund. The value of your investment in a non-institutional class of a Columbia money market fund held in an eligible account may be aggregated with your investments in other funds in the Columbia family of funds to obtain a breakpoint discount through a Right of Accumulation. Non-institutional class investments in Columbia money market funds may also be included in the aggregation for a Statement of Intent for shares that have been charged a commission.

C.  How do I obtain a breakpoint discount?

The steps necessary to obtain a breakpoint discount depend on how your account is maintained with the Columbia family of funds. To obtain any of the above breakpoint discounts, you must notify your financial advisor at the time you purchase shares of the existence of each eligible account maintained by you or your immediate family. It is the sole responsibility of your financial advisor to ensure that you receive discounts for which you are eligible, and the Fund is not responsible for a financial advisor's failure to apply the eligible discount to your account. You may be asked by the Fund or your financial advisor for account statements or other records to verify your discount eligibility, including, where applicable, records for accounts opened with a different financial advisor and records of accounts established by members of your immediate family. If you own shares exclusively through an account maintained with the Fund's transfer agent, Columbia Management Services, Inc., you will need to provide the foregoing information to a Columbia Management Services, Inc. representative at the time you purchase shares.

D.  How can I obtain more information about breakpoint discounts?

Certain investors, including affiliates of the Fund, broker/dealers and their affiliates, investors in wrap-fee programs through fee-based advisers or certain retirement plans, certain shareholders of funds that were reorganized into other Columbia funds and investors using the proceeds of redemptions of Fund shares or of certain Bank of America trust or similar accounts, may purchase shares at a reduced sales charge or net asset value, which is the value of a fund share excluding any sales charges. CDSCs may also be waived for redemptions under a systematic withdrawal program, in connection with the death or post-purchase disability of a shareholder, certain medical expenses, charitable gifts, involuntary and tax-related redemptions, or when the selling broker/dealer has agreed to waive or return its commission. Restrictions may apply to certain accounts and certain transactions. Further information regarding these discounts ma y be found in the Fund's SAI, which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611.

Class B shares Your purchases of Class B shares are at Class B's net asset value. No new Class B share accounts may be established in the Fund. However, Class B share accounts established prior to February 3, 2006 may nonetheless purchase additional Class B shares, so long as those purchases do not result in the account holding $50,000 or more of Class B shares (including for this purpose the combined value of all eligible accounts maintained by you that would be used to determine eligibility for reduced sales charges on Class A shares). In the event that an existing Class B shareholder seeks to add funds to such an account so that the balance would be in excess of $49,999, the amount in excess may be invested in Class A shares without the imposition of the minimum investment requirement for Class A shares. Such purchases of Class A shares will be sub ject to the applicable sales load imposed on such purchases. See "Class A Sales Charges" on page 12.

Class B shares have no front-end sales charge, but they do carry a CDSC that is imposed only on shares sold within six years of purchase. The CDSC declines over the six years and disappears in the seventh year. The distributor pays

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your financial advisor an up-front commission on sales of Class B shares as described in the chart below. In addition, Class B shares bear ongoing service and distribution fees that are higher than those borne by Class A shares.

Purchases of less than $50,000⁽¹⁾:

Class B Sales Charges

Holding period after purchase	% deducted when shares are sold(2)
Through first year		5.00
Through second year		4.00
Through third year		3.00
Through fourth year		3.00
Through fifth year		2.00
Through sixth year		1.00
Longer than six years		0.00

(1)  Only applicable to accounts opened prior to February 3, 2006.

(2)  Applied to the net asset value at the time of purchase or sale, whichever is lower.

In addition, from the annual fee of 0.75% of the value of your shares paid out of your Fund assets as Rule 12b-1 fees, the distributor receives 0.50% of the value of the shares for each of the first eight years, or an aggregate 4.00% over eight years, which will offset the commission it paid to your financial advisor. Your financial advisor is paid the remaining 0.25% as an ongoing commission for the life of your investment.

The conversion of Class B shares to Class A shares occurs automatically eight years after purchase.

Class C shares Your purchases of Class C shares are at Class C's net asset value. Although Class C shares have no front-end sales charge, they carry a CDSC of 1.00% that is applied to shares sold within the first year after they are purchased. After holding shares for one year, you may sell them at any time without paying a CDSC. The distributor pays your financial advisor an up-front commission of 1.00% on your purchase of Class C shares, for which the distributor is repaid from the ongoing annual fee of 1.00% of the value of your shares paid out of your Fund assets as Rule 12b-1 fees, which is higher than the Rule 12b-1 fees borne by Class A and Class B shares.

Class C Sales Charges

Holding period after purchase	% deducted when shares are sold(1)
Through one year		1.00
Longer than one year		0.00

(1)  Applied to the net asset value at the time of purchase or sale, whichever is lower.

A 1.00% annual commission is paid to your financial advisor and the distributor over the life of your investment out of your Fund assets.

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HOW TO EXCHANGE SHARES

You may exchange your shares for shares of the same share class (and in some cases, certain other classes) of another fund distributed by Columbia Management Distributors, Inc. at net asset value. If your shares are subject to a CDSC, you will not be charged a CDSC upon the exchange. However, when you sell the shares acquired through the exchange, the shares sold may be subject to a CDSC, depending upon when you originally purchased the shares you are exchanging. For purposes of computing the CDSC, the length of time you have owned your shares will be computed from the date of your original purchase and the applicable CDSC will be the CDSC of the original fund. Shareholders of Columbia Acorn Funds that qualify to purchase Class A shares at net asset value may exchange their Class A shares for Class Z shares of another fund distributed by Columbia Management Distributors, Inc. (See the SAI for a description of these situations.) Unless your account is part of a tax-deferred retirement plan, an exchange is a taxable event, and you may realize a gain or a loss for tax purposes. The Fund may terminate your exchange privilege if the adviser determines that your exchange activity is likely to adversely impact its ability to manage the Fund. See "Fund Policy on Trading of Fund Shares" for the Fund's policy. To exchange by telephone, call 1-800-422-3737. Please have your account and taxpayer identification numbers available when calling.

You also may exchange your shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet exchanges. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

HOW TO SELL SHARES

Your financial advisor can help you determine if and when you should sell your shares. You may sell shares of the Fund on any regular business day that the NYSE is open.

When the Fund receives your sales request in "good form," shares will be sold at the next calculated net asset value. "Good form" means that the Fund's transfer agent has all information and documentation it deems necessary to effect your order. For example, when selling shares by letter of instruction, "good form" means (i) your letter has complete instructions, the proper signatures and Medallion Signature Guarantees, (ii) if applicable, you have included any certificates for shares to be sold, and (iii) any other required documents are attached. For additional documents required for sales by corporations, agents, fiduciaries, surviving joint owners and other legal entities, please call 1-800-345-6611. Retirement plan accounts have special requirements; please call 1-800-799-7526 for more information.

The Fund will generally send proceeds from the sale to you within seven days (usually on the next business day after your request is received in "good form"). However, if you purchased your shares by check, the Fund may delay sending the proceeds from the sale of your shares for up to 10 days after your purchase to protect against checks that are returned. No interest will be paid on uncashed redemption checks. Redemption proceeds may be paid in securities rather than cash, under certain circumstances. For more information, see the paragraph "Non-Cash Redemptions" under the section "How to Sell Shares" in the SAI.

During any 90-day period for any one shareholder, the Fund is obligated to redeem shares solely in cash up to the lesser of $250,000 or 1% of the Fund's net assets. Redemptions in excess of these limits will normally be paid in cash, but may be paid wholly or partly by an in-kind distribution of securities.

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Outlined below are the various options for selling shares:

Method	Instructions
Through your financial advisor	You may call your financial advisor to place your sell order. To receive the current trading day's price, your financial advisor must receive your request prior to the close of regular trading on the NYSE, usually 4:00 p.m. Eastern time. Your financial advisor may charge you fees for executing a redemption for you.
By exchange	You or your financial advisor may sell Fund shares by exchanging from the Fund into the same share class (and, in some cases, certain other classes) of another fund distributed by Columbia Management Distributors, Inc. at no additional cost. To exchange by telephone, call 1-800-422-3737.
By telephone	You or your financial advisor may sell Fund shares by telephone and request that a check be sent to your address of record by calling 1-800-422-3737, unless you have notified the Fund of an address change within the previous 30 days. The dollar limit for telephone sales is $100,000 in a 30-day period. You do not need to set up this feature in advance of your call. Certain restrictions apply to retirement accounts. For details, call 1-800-799-7526.
By mail	You may send a signed letter of instruction or, if applicable, stock power form along with any share certificates to be sold to the address below. In your letter of instruction, note the Fund's name, share class, account number, and the dollar value or number of shares you wish to sell. All account owners must sign the letter. Signatures must be guaranteed by either a bank, a member firm of a national stock exchange or another eligible guarantor that participates in the Medallion Signature Guarantee Program for amounts over $100,000 or for alternate payee or mailing instructions. Additional documentation is required for sales by corporations, agents, fiduciaries, surviving joint owners and individual retirement account owners. For details, call 1-800-345-6611. Mail your letter of instruction to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By wire	You may sell Fund shares and request that the proceeds be wired to your bank. You must set up this feature prior to your request. Be sure to complete the appropriate section of the account application for this feature. Generally, the value of your redemption must be at least equal to $500 in order to have the sale proceeds wired to your bank. There is a $7.50 charge for wiring sale proceeds to your bank. (The transfer agent may waive this fee for omnibus and nominee accounts.) Your bank may charge additional fees for such wire transfer.
By systematic withdrawal plan	You may automatically sell a specified dollar amount or percentage of your account on a monthly, quarterly or semiannual basis and have the proceeds sent to you if your account balance is at least $5,000. The $5,000 minimum account balance requirement is waived for wrap accounts. This feature is not available if you hold your shares in certificate form. All dividend and capital gains distributions must be reinvested. Be sure to complete the appropriate section of the account application for this feature.
By electronic funds transfer	You may sell Fund shares and request that the proceeds be electronically transferred to your bank. Proceeds may take up to two business days to be received by your bank. You must set up this feature prior to your request. Be sure to complete the appropriate section of the account application for this feature.
Through the internet	You may sell Fund shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet redemptions. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

FUND POLICY ON TRADING OF FUND SHARES

The interests of the Fund's long-term shareholders may be adversely affected by certain short-term trading activity by Fund shareholders. Such short-term trading activity, when excessive, has the potential to interfere with efficient portfolio management, generate transaction and other costs, dilute the value of Fund shares held by long-term shareholders and have other adverse effects on the Fund. This type of excessive short-term trading activity is referred to herein as "market timing." For purposes of this section, the "Columbia Funds" are the Columbia, Columbia Acorn Trust and Wanger Advisors trust families of mutual funds. The Columbia Funds are not intended as vehicles for market timing. The Board of Trustees of the Fund has adopted the policies and procedures set forth below with respect to frequent trading of the Fund's shares.

The Fund, directly and through its agents, takes various steps designed to deter and curtail market timing. For example, if the Fund detects that any shareholder has conducted two "round trips" (as defined below) in the Fund

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in any 28-day period, except as noted below with respect to orders received through omnibus accounts, the Fund will reject the shareholder's future purchase orders, including exchange purchase orders, involving any Columbia fund (other than a money market fund). In addition, if the Fund determines that any person, group or account has engaged in any type of market timing activity (independent of the two-round-trip limit), the Fund may, in its discretion, reject future purchase orders by the person, group or account, including exchange purchase orders, involving the same or any other Columbia fund, and also retains the right to modify these market timing policies at any time without prior notice.

The rights of shareholders to redeem shares of the Fund are not affected by any of the limits mentioned above. However, certain funds (other than the Funds) impose a redemption fee on the proceeds of fund shares that are redeemed or exchanged within 60 days of their purchase.

For these purposes, a "round trip" is a purchase by any means into a Columbia fund followed by a redemption, of any amount, by any means out of the same Columbia fund. Under this definition, an exchange into the Fund followed by an exchange out of the Fund is treated as a single round trip. Also for these purposes, where known, accounts under common ownership or control generally will be counted together. Accounts maintained or managed by a common intermediary, such as an adviser, selling agent or trust department, generally will not be considered to be under common ownership or control.

Purchases, redemptions and exchanges made through the Columbia Funds' Automatic Investment Plan, Systematic Withdrawal Plan or similar automated plans are not subject to the two-round-trip limit. Purchases, redemptions and exchanges made by Columbia Thermostat Fund are also not subject to the two round-trip limit. The two-round-trip limit may be modified for, or may not be applied to, accounts held by certain retirement plans to conform to plan limits, considerations relating to the Employee Retirement Income Security Act of 1974 or regulations of the Department of Labor, and for certain asset allocation or wrap programs.

The practices and policies described above are intended to deter and curtail market timing in the Fund. However, there can be no assurance that these policies, individually or collectively, will be totally effective in this regard because of various factors. In particular, a substantial portion of purchase, redemption and exchange orders are received through omnibus accounts. Omnibus accounts, in which shares are held in the name of an intermediary on behalf of multiple beneficial owners, are a common form of holding shares among financial intermediaries and retirement plans. The Fund typically is not able to identify trading by a particular beneficial owner through an omnibus account, which may make it difficult or impossible to determine if a particular account is engaged in market timing. Consequently, there is the risk that the Fund may not be able to identify, deter or curtail certain market timing do anything in response t o market timing that occurs in the Fund, which may result in certain shareholders being able to market time the Fund while the shareholders in the Fund bear the burden of such activities.

Certain financial intermediaries (including certain retirement plan service providers whose clients include, among others, various retirement plans sponsored by Bank of America and its affiliates for the benefit of its employees (the "Bank of America retirement plan service providers")) have different policies regarding monitoring and restricting market timing in the underlying beneficial owner accounts that they maintain through an omnibus account that may be more or less restrictive than the Fund practices discussed above. In particular, the Bank of America retirement plan service plan providers permit the reinstatement of future purchase orders for shares of the Fund following various suspension periods. If an intermediary does not enforce the Fund's policy, the intermediary must either provide data transparency to Columbia Management or Columbia Management must

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determine that the intermediary's policy taken in its entirety provides protection to fund shareholders that are generally commensurate with the Fund's policy.

The Fund seeks to act in a manner that it believes is consistent with the best interests of Fund shareholders in making any judgments regarding market timing. Neither the Fund nor its agents shall be held liable for any loss resulting from rejected purchase orders or exchanges.

OTHER INFORMATION ABOUT YOUR ACCOUNT

How the Fund's Share Price is Determined The price of each class of the Fund's shares is based on its net asset value. The net asset value is determined at the close of regular trading on the NYSE, usually 4:00 p.m. Eastern time, on each business day that the NYSE is open for trading (typically Monday through Friday). Net asset value is not determined on days on which the NYSE is closed for trading.

When you request a transaction, it will be processed at the net asset value per share (plus any applicable sales charges) next determined after your request is received in "good form" by the distributor. In most cases, in order to receive that day's price, the distributor must receive your order before that day's transactions are processed. If you request a transaction through your financial advisor, your financial advisor must receive your order by the close of trading on the NYSE to receive that day's price.

The Fund determines its net asset value for each share class by dividing each class's total net assets by the number of that class's outstanding shares. In determining the net asset value, the Fund must determine the value of each security in its portfolio at the close of each trading day. Securities for which market quotations are available are valued each day at the current market value. However, where market quotations are unavailable, or when the adviser believes that subsequent events have made them unreliable, the Fund may use other data to determine the fair value of the securities.

The Fund has retained an independent statistical fair value pricing service to assist in the fair valuation process for securities principally traded in a foreign market in order to adjust for possible changes in value that may occur between the close of the foreign exchange and the time at which Fund shares are priced. The use of an independent fair value pricing service is intended to and may decrease the opportunities for time zone arbitrage transactions. There can be no assurance that the use of an independent fair value pricing service will successfully decrease arbitrage opportunities. If a security is valued at a "fair value," that value may be different from the last quoted market price for the security.

You can find the daily prices of some share classes for the Fund in most major daily newspapers under the heading of "Columbia." You can find daily prices for all share classes by visiting www.columbiafunds.com.

Share Certificates Share certificates are not available for any class of shares offered by the Fund. If you currently hold previously issued share certificates, you will not be able to sell your shares until you have returned your share certificates to the transfer agent.

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Dividends, Distributions, and Taxes The Fund has the potential to make the following distributions:

Types of Distributions

Dividends	Represents interest and dividends earned from securities held by the Fund, net of expenses incurred by the Fund.
Capital gains	Represents net long-term capital gains on sales of securities held for more than one year and net short-term capital gains, which are gains on sales of securities held for a one-year period or less.

UNDERSTANDING FUND DISTRIBUTIONS

The Fund may earn income from the securities it holds. The Fund also may realize capital gains or losses on sales of its securities. The Fund intends to distribute substantially all of its net investment income and capital gains to shareholders each year. As a shareholder, you are entitled to a portion of the Fund's income and capital gains based on the number of shares you own at the time these distributions are declared.

Distribution Options The Fund distributes any dividends in June and December and any capital gains (including short-term capital gains) at least annually. You can choose one of the options listed in the table below for these distributions when you open your account. To change your distribution option call 1-800-345-6611.

If you do not indicate on your application or at the time your account is established your preference for handling distributions, the Fund will automatically reinvest all distributions in additional shares of the Fund.

Distribution Options

Reinvest all distributions in additional shares of the Fund

Reinvest all distributions in shares of another fund

Receive dividends in cash (see options below) and reinvest capital gains

Receive all distributions in cash (with one of the following options):

•  send the check to your address of record

•  send the check to a third-party address

•  transfer the money to your bank via electronic funds transfer

Distributions of $10 or less will automatically be reinvested in additional Fund shares. If you elect to receive distributions by check and the check is returned as undeliverable, all subsequent distributions will be reinvested in additional shares of the Fund.

Taxes Unless you are an entity exempt from income taxes or invest under a retirement account, regardless of whether you receive your distributions in cash or reinvest them in additional Fund shares, all Fund distributions are subject to federal income tax. Depending on where you live, distributions also may be subject to state and local income taxes.

The Fund intends to elect to be treated and to qualify each year as a regulated investment company. A regulated investment company is not subject to tax at the corporate level on income and gains from investments that are distributed to shareholders in accordance with applicable law. However, the Fund's failure to qualify as a regulated investment company could result in corporate level taxation, and consequently, a reduction in income available for distribution to shareholders.

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In general, any distributions of dividends, interest and short-term capital gains (determined by how long the Fund held the investments that generated them) are taxable as ordinary income, unless such dividends are "qualified dividend income" (as defined in the Internal Revenue Code) eligible for a reduced rate of tax. Properly designated distributions of long-term capital gains (determined by how long the Fund held the investments that generated them) are generally taxable as such, regardless of how long you have held your Fund shares. You will be provided with information each year regarding the amount of ordinary income and capital gains distributed to you for the previous year and any portion of your distribution which is exempt from state and local taxes. Long-term capital gain rates have been reduced — in general, to 15% with lower rates applying to taxpayers in the 10% and 15% rate brackets — for taxable years b eginning before January 1, 2011. Distributions are taxable to you even if they are paid from income or gains earned by the Fund before you made your investment (and thus were included in the price you paid). Your investment in the Fund may have additional personal tax implications. Please consult your tax advisor about federal, state, local or other applicable tax laws.

In addition to the dividends and capital gains distributions made by the Fund, you may realize a capital gain or loss when selling or exchanging shares of the Fund. Such transactions also may be subject to federal, state and local income tax.

Board of Trustees

The Fund is governed by its Board of Trustees. More than 75% of the Fund's Trustees are independent, meaning that they have no affiliation with the adviser or the Funds, apart from their positions as Trustees and the personal investments they may have made as private individuals.

The independent Trustees bring backgrounds in business and the professions and academia to their task of working with the Funds' officers to establish the policies and oversee the activities of the Funds. Among the Trustees' responsibilities are selecting the investment adviser for the Funds; negotiating the advisory agreements; reviewing other contracts; approving investment policies; monitoring Fund operations, performance, and costs; and nominating or selecting new Trustees.

Each Trustee serves a Fund until his or her retirement, resignation, death or removal; or otherwise as specified in the Trust's organizational documents. It is expected that every five years the Trustees will call a meeting of shareholders to elect Trustees. A Trustee must retire at the end of the year in which he or she attains the age of 75. Any Trustee may be removed at a shareholders' meeting by a vote representing two-thirds of the net asset value of all shares of the Funds of the Trust. The mailing address for the Trustees and officers is 227 W. Monroe, Suite 3000, Chicago, Illinois 60606.

For more detailed information on the Board of Trustees, please refer to the SAI.

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Managing the Fund

INVESTMENT ADVISER

Columbia Wanger Asset Management, L.P. (CWAM), located at 227 West Monroe Street, Suite 3000, Chicago, Illinois 60606, is the Fund's investment adviser and is responsible for the Fund's management, subject to the oversight of the Fund's Board of Trustees. CWAM and its predecessor have managed mutual funds, including the Fund, since 1992. In its duties as investment adviser, CWAM runs the Fund's day-to-day business, including making investment decisions and placing all orders for the purchase and sale of the Fund's portfolio securities.

CWAM was previously named Liberty Wanger Asset Management, L.P. and its predecessor was named Wanger Asset Management, L.P. (WAM). CWAM is a wholly owned subsidiary of Columbia Management Group, LLC, which is an indirect wholly owned subsidiary of Bank of America Corporation. As of December 31, 2006, CWAM managed more than $32.9 billion in assets.

CWAM's advisory fee for managing the Fund in 2006 was 0.86% of the Fund's average daily net assets. CWAM also received an administrative fee from the Fund in 2006 of 0.04% of the Fund's average daily net assets. A discussion of the factors considered by the Fund's Board of Trustees in approving the Fund's investment advisory contract is included in the Fund's annual report to shareholders for the period ended December 31, 2006.

PORTFOLIO MANAGER

CWAM uses a team to assist the lead portfolio manager in managing the Fund. Team members share responsibility for providing ideas, information and knowledge in managing the Fund, and each team member has one or more particular areas of expertise. The portfolio manager is responsible for making daily investment decisions and utilizing the management team's input and advice when making buy and sell determinations.

Robert A. MohnLead portfolio manager
Robert Mohn is a vice president of the Trust. He has been a member of the domestic analytical team at CWAM and its predecessor since August 1992. He has managed Columbia Acorn USA since its inception in 1996, co-managed Columbia Acorn Fund since May 2003, and also manages Wanger U.S. Smaller Companies, a mutual fund underlying variable insurance products, and the U.S. fund of an investment company whose shares are offered only to non-U.S. investors. Mr. Mohn also is a vice president of Wanger Advisors Trust and the director of domestic research for CWAM.

The SAI provides additional information about the portfolio manager's compensation, other accounts managed and ownership of securities in the Fund.

LEGAL PROCEEDINGS

The Trust, CWAM and the trustees of the Trust (collectively, the "Columbia defendants") are named as defendants in class and derivative complaints, which were consolidated in a Multi-District Action in the federal district court for the District of Maryland on February 20, 2004 (the "MDL Action"). These lawsuits contend that defendants permitted certain investors to market time their trades in certain Columbia Acorn Funds. The MDL Action All claims against the Trust and its independent trustees have been dismissed; however, the interested trustees of the Trust are still parties to the MDL Action.

On March 21, 2005, a class action complaint was filed against the Trust in the Superior Court of the Commonwealth of Massachusetts seeking to rescind the contingent deferred sales charges assessed upon redemption of Class B shares of Columbia Acorn Funds due to the alleged market timing of the Columbia Acorn

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Funds. In addition to the rescission of sales charges, plaintiffs seek recovery of actual damages, attorneys' fees and costs. The case has been transferred to the MDL Action in the federal district court of Maryland.

The Trust and CWAM are also defendants in a class action lawsuit, filed on November 13, 2003 in the Circuit Court of the Third Judicial Circuit, Madison County, Illinois, that alleges, in summary, that the Trust and CWAM exposed shareholders of Columbia Acorn International to trading by market timers by allegedly (a) failing to properly evaluate daily whether a significant event affecting the value of that fund's securities had occurred after foreign markets had closed but before the calculation of the fund's net asset value; (b) failing to implement the fund's portfolio valuation and share pricing policies and procedures; and (c) failing to know and implement applicable rules and regulations concerning the calculation of net asset value ("Fair Valuation Lawsuit"). On April 5, 2005, the United States Court of Appeals for the Seventh Circuit ruled that the plaintiffs' state law claims were preempted under federal law resulting in the dismissal of plaintiffs' complaint. Plaintiffs appealed the Seventh Circuit's ruling to the United States Supreme Court. On June 15, 2006, the Supreme Court reversed the Seventh Circuit's ruling on jurisdictional grounds, and the case ultimately was remanded to the state court.

On April 4, 2006, the plaintiffs and the Columbia defendants named in the MDL Action executed an agreement in principle intended to fully resolve all of the lawsuits consolidated in the MDL Action as well as the Fair Valuation Lawsuit. The court entered a stay after the parties executed the agreement in principle. The settlement is subject to court approval.

In 2004, CWAM and the trustees of the Columbia Acorn Trust were named as defendants in certain purported shareholder class and derivative actions making claims, including claims under the Investment Company and the Investment Advisers Acts of 1940 and state law. Certain Columbia Acorn Funds were named as nominal defendants. The suits allege, inter alia, that the fees and expenses paid by the funds are excessive and that the funds' advisers and their affiliates inappropriately used fund assets to distribute the funds and for other improper purposes. On March 2, 2005, the actions were consolidated in the Massachusetts federal court as In re Columbia Entities Litigation. The plaintiffs filed a consolidated amended complaint on June 9, 2005. On November 30, 2005, the judge dismissed all claims by plaintiffs and entered final judgment in favor of the defendants. The plaintiffs appealed to the United States Court of Appeals for the First Circuit on December 30, 2005. A stipulation and settlement agreement dated January 19, 2007 was filed in the First Circuit on February 14, 2007, with a joint stipulation of dismissal and motion for remand to obtain district court approval of the settlement. The joint motion was granted and the appeal was dismissed. On March 6, 2007, the case was remanded to the District Court, where the parties will seek court approval of the settlement. The terms of the proposed settlement, if approved, will require payments by the funds' adviser and/or its affiliates, including payment of plaintiffs' attorneys' fees and notice to class members. In the event that the settlement is not approved, the plaintiffs may elect to g o forward with their appeal and no opinion is expressed regarding the likely outcome or financial impact of such an appeal on any fund.

On or about January 11, 2005, a putative class action lawsuit was filed in federal district court in Massachusetts against the Trust and its trustees, along with Columbia Management Advisors, LLC, the sub-administrator of the Wanger Advisors Funds and the Columbia Acorn Funds. The plaintiffs allege that the defendants failed to submit Proof of Claims in connection with settlements of securities class action lawsuits filed against companies in which the Columbia Acorn Funds held positions. The complaint seeks compensatory and punitive damages, and the disgorgement of all fees paid to Columbia Management Advisors, LLC. Plaintiffs have voluntarily dismissed the Trust and its independent trustees.

23

Managing the Fund

The Trust and CWAM intend to defend these suits vigorously.

As a result of these matters or any adverse publicity or other developments resulting from them, there may be increased redemptions or reduced sales of Fund shares, which could increase transaction costs or operating expenses, or have other adverse consequences for the Fund.

However, based on currently available information, the Trust believes that the likelihood that these lawsuits will have a material adverse impact on any fund is remote, and CWAM believes that the lawsuits are not likely to materially affect its ability to provide investment management services to the Fund.

Other Investment Strategies and Risks

The Fund's principal investment strategies and associated risks are described under "The Fund — Principal Investment Strategies" and "The Fund — Principal Investment Risks." This section describes other investments the Fund may make and the risks associated with them. In seeking to achieve its investment goal, the Fund may invest in various types of securities and engage in various investment techniques, which are not the principal focus of the Fund and therefore are not described in this prospectus. These types of securities and investment practices and their associated risks are identified and discussed in the Fund's SAI, which you may obtain free of charge (see back cover). The adviser may elect not to buy any of these securities or use any of these techniques. The Fund may not always achieve its investment goal. Except as otherwise noted, approval by the Fund's shareholders is not required to modify or change the F und's investment strategies.

THE INFORMATION EDGE

The Fund generally invests in entrepreneurially managed smaller- and mid-sized companies that it believes are not as well known by financial analysts and whose position in a niche creates the opportunity for superior earnings-growth potential. CWAM may identify what it believes are important economic, social or technological trends (for example, the growth of outsourcing as a business strategy, or the productivity gains from the increasing use of technology) and try to identify companies it thinks will benefit from these trends.

24

Other Investment Strategies and Risks

In making investments for the Fund, CWAM relies primarily on independent, internally generated research to uncover companies that may be less well known than the more popular names. To find these companies, CWAM compares growth potential, financial strength and fundamental value among companies.

Growth Potential	Financial Strength	Fundamental Value
• superior technology • innovative marketing • managerial skill • market niche • good earnings prospects • strong demand for product	• low debt • adequate working capital • conservative accounting practices • adequate profit margin	• reasonable stock price relative to growth potential and financial strength • valuable assets
The realization of this growth potential would likely produce superior performance that is sustainable over time.	A strong balance sheet gives management greater flexibility to pursue strategic objectives and is important to maintaining a competitive advantage.	Once CWAM uncovers an attractive company, it identifies a price that it believes would also make the stock a good value.

LONG-TERM INVESTING

CWAM's analysts continually screen companies and make contact with more than 1,000 companies around the globe each year. To accomplish this, CWAM analysts often talk directly to top management, vendors, suppliers and competitors.

In managing the Fund, CWAM tries to maintain lower taxes and transaction costs by investing with a long-term time horizon (at least two to five years). However, securities purchased on a long-term basis may be sold within 12 months after purchase due to changes in the circumstances of a particular company or industry, or changes in general market or economic conditions.

DERIVATIVE STRATEGIES

The Fund may enter into a number of derivative strategies, including those that employ futures, options, straddles or similar transactions, to gain or reduce exposure to particular securities or markets. These strategies, commonly referred to as derivatives, involve the use of financial instruments whose values depend on, or are derived from, the value of an underlying security, index or currency. The Fund may use these strategies to adjust the Fund's sensitivity to changes in interest rates, or for other hedging purposes (i.e., attempting to offset a potential loss in one position by establishing an interest in an opposite position). Derivative strategies involve the risk that they may exaggerate a loss, potentially losing more money than the actual cost of the underlying security, or limit a potential gain. Also, with some derivative strategies there is a risk that the other party to the transaction may fail to honor its contr act terms, causing a loss to the Fund or that the Fund may not be able to find a suitable derivative transaction counterparty, and thus may be unable to invest in derivatives altogether.

TEMPORARY DEFENSIVE STRATEGIES

At times, CWAM may determine that adverse market conditions make it desirable to temporarily suspend the Fund's normal investment activities. During such times, the Fund may, but is not required to, invest in cash or high-quality, short-term debt securities, without limit. Taking a temporary defensive position may prevent the Fund from achieving its investment goal.

25

Financial Highlights

The financial highlights table is intended to help you understand the Fund's financial performance. Information is shown for the Fund's last five fiscal years, which run from January 1 to December 31. Certain information in the table reflects the financial results for a single Class A, B or C share. The total returns in the table represent the return that you would have earned (or lost) on an investment in the Fund (assuming reinvestment of all dividends and distributions). This information has been derived from the Fund's financial statements, which have been audited for the years ended December 31, 2004, 2005 and 2006 by PricewaterhouseCoopers LLP, an independent registered public accounting firm, whose report, along with the Fund's financial statements, is included in the Fund's annual report. The information for the years ended December 31, 2002 and 2003 is included in the Fund's financial statements that have been audited b y another independent registered public accounting firm, whose report expressed an unqualified opinion on those financial statements and highlights. You can request a free annual report containing those financial statements by calling 1-800-345-6611.

Columbia Acorn USA

	Year Ended December 31,
	2006			2005			2004			2003			2002
	Class A			Class A			Class A			Class A			Class A
Net Asset Value — Beginning of Period ($)		26.52			24.77			20.74			14.18			17.50
Income from Investment Operations ($):
Net investment loss(a)		(0.10	)		(0.01	)		(0.24	)		(0.22	)		(0.19	)
Net realized and unrealized gain (loss)		2.21			3.13			4.41			6.78			(3.13	)
Total from Investment Operations		2.11			3.12			4.17			6.56			(3.32	)
Less Distributions Declared to Shareholders ($):
From net realized gains		(0.61	)		(1.37	)		(0.14	)		—			—
Total Distributions Declared to Shareholders		(0.61	)		(1.37	)		(0.14	)		—			—
Net asset value — End of Period ($)		28.02			26.52			24.77			20.74			14.18
Total Return (%)(b)		7.95	(c)		12.68	(c)		20.12	(c)		46.26			(18.97	)
Ratios to Average Net Assets/Supplemental Data (%):
Expenses(d)		1.26			1.31			1.51			1.65			1.74
Net investment loss(d)		(0.35	)		(0.02	)		(1.08	)		(1.26	)		(1.21	)
Waiver/reimbursement		0.01			0.01			0.02			—			—
Portfolio turnover rate (%)		13			13			18			7			31
Net assets at end of period (000's) ($)		245,552			168,922			112,509			89,650			32,422

(a)   Per share data was calculated using average shares outstanding during the period.

(b)   Total return at net asset value assuming all distributions reinvested and no initial sales charge or contingent deferred sales charge.

(c)  Had the investment adviser and/or transfer agent not waived and/or reimbursed a portion of expenses, total return would have been reduced.

(d)  The benefits derived from custody fees paid indirectly had no impact.

26

Financial Highlights

Columbia Acorn USA

	Year Ended December 31,
	2006			2005			2004			2003			2002
	Class B			Class B			Class B			Class B			Class B
Net asset value — Beginning of period ($)		25.61			24.14			20.36			14.01			17.40
Income from Investment Operations ($):
Net investment loss(a)		(0.27	)		(0.18	)		(0.39	)		(0.32	)		(0.29	)
Net realized and unrealized gain (loss)		2.14			3.02			4.31			6.67			(3.10	)
Total from Investment Operations		1.87			2.84			3.92			6.35			(3.39	)
Less Distributions Declared to Shareholders ($):
From net realized gains		(0.61	)		(1.37	)		(0.14	)		—			—
Total Distributions Declared to Shareholders		(0.61	)		(1.37	)		(0.14	)		—			—
Net asset value — End of period ($)		26.87			25.61			24.14			20.36			14.01
Total Return (%)(b)		7.29	(c)		11.84	(c)		19.26	(d)		45.32			(19.48	)
Ratios to Average Net Assets/Supplemental Data (%):
Expenses(d)		1.93			2.00			2.23			2.30			2.39
Net investment loss(d)		(1.01	)		(0.72	)		(1.80	)		(1.91	)		(1.86	)
Waiver/reimbursement		0.02			0.01			0.02			—			—
Portfolio turnover rate (%)		12			13			18			7			31
Net assets at end of period (000's) ($)		65,040			73,168			72,643			66,175			37,478

(a)  Per share data was calculated using average shares outstanding during the period.

(b)  Total return at net asset value assuming all distributions reinvested and no initial sales charge or contingent deferred sales charge.

(c)  Had the investment adviser and/or transfer agent not waived and/or reimbursed a portion of expenses, total return would have been reduced.

(d)  The benefits derived from custody fees paid indirectly had no impact.

27

Financial Highlights

Columbia Acorn USA

	Year Ended December 31,
	2006			2005			2004			2003			2002
	Class C			Class C			Class C			Class C			Class C
Net asset value — Beginning of Period ($)		25.59			24.14			20.36			14.01			17.40
Income from Investment Operations ($):
Net investment loss(a)		(0.30	)		(0.20	)		(0.39	)		(0.32	)		(0.29	)
Net realized and unrealized gain (loss)		2.13			3.02			4.31			6.67			(3.10	)
Total from Investment Operations		1.83			2.82			3.92			6.35			(3.39	)
Less Distributions Declared to Shareholders ($):
From net realized gains		(0.61	)		(1.37	)		(0.14	)		—			—
Total Distributions Declared to Shareholders		(0.61	)		(1.37	)		(0.14	)		—			—
Net asset value — End of Period ($)		26.81			25.59			24.14			20.36			14.01
Total return (%)(b)		7.14	(c)		11.76	(c)		19.26	(c)		45.32			(19.48	)
Ratios to Average Net Assets/Supplemental Data (%):
Expenses(d)		2.05			2.10			2.23			2.30			2.39
Net investment loss(d)		(1.14	)		(0.81	)		(1.80	)		(1.91	)		(1.86	)
Waiver/reimbursement		0.01			0.01			0.02			—			—
Portfolio turnover rate (%)		13			13			18			7			31
Net assets at end of period (000's) ($)		55,306			42,844			39,643			35,662			18,313

(a)  Per share data was calculated using average shares outstanding during the period.

(b)  Total return at net asset value assuming all distributions reinvested and no initial sales charge or contingent deferred sales charge.

(c)  Had the investment adviser and/or transfer agent not waived and/or reimbursed a portion of expenses, total return would have been reduced.

(d)  The benefits derived from custody fees paid indirectly had no impact.

28

Appendix

Hypothetical Investment and Expense Information

The Fund is required to disclose the following supplemental hypothetical investment information, which provides additional information about the effect of the expenses paid by the Fund, including investment advisory fees and other Fund costs, on the Fund's returns over a 10-year period. The tables show the estimated expenses that would be charged on a hypothetical investment of $10,000 in each class of the Fund assuming a 5% return each year, the cumulative return after fees and expenses, and the hypothetical year-end balance after fees and expenses. The tables also assume that all dividends and distributions are reinvested and that Class B shares convert to Class A shares after eight years. The annual expense ratios used for the Fund, which are the same as those stated in the Annual Fund Operating Expenses table, are presented in the tables, and are net of any contractual fee waivers or expense reimbursements for the period of the contractual commitment. Your actual costs may be higher or lower. The tables shown below reflect the maximum initial sales charge for Class A shares but do not reflect any contingent deferred sales charges which may be payable on redemption. If contingent deferred sales charges were reflected, the "Hypothetical Year-End Balance After Fees and Expenses" amounts shown would be lower and the "Annual Fees and Expenses" amounts shown would be higher. As noted previously, the Fund's minimum investment for initial purchases or exchanges is $75,000.

Columbia Acorn USA — Class A Shares

Maximum Sales Charge 5.75%					Initial Hypothetical Investment Amount $10,000.00						Assumed Rate of Return 5%
Year		Cumulative Return Before Fees & Expenses			Annual Expense Ratio			Cumulative Return After Fees & Expenses			Hypothetical Year-End Balance After Fees & Expenses		Annual Fees & Expenses(1)
	1		5.00	%		1.30	%		-2.26	%(2)	$	9,773.73	$	699.79
	2		10.25	%		1.30	%		1.35	%	$	10,135.35	$	129.41
	3		15.76	%		1.30	%		5.10	%	$	10,510.36	$	134.20
	4		21.55	%		1.30	%		8.99	%	$	10,899.24	$	139.16
	5		27.63	%		1.30	%		13.03	%	$	11,302.52	$	144.31
	6		34.01	%		1.30	%		17.21	%	$	11,720.71	$	149.65
	7		40.71	%		1.30	%		21.54	%	$	12,154.38	$	155.19
	8		47.75	%		1.30	%		26.04	%	$	12,604.09	$	160.93
	9		55.13	%		1.30	%		30.70	%	$	13,070.44	$	166.88
	10		62.89	%		1.30	%		35.54	%	$	13,554.04	$	173.06
Total Gain After Fees and Expenses											$	3,554.04
Total Annual Fees and Expenses													$	2,052.58

(1)  Annual Fees and Expenses are calculated based on the average between the beginning and ending balance for each year. All information is calculated on an annual compounding basis.

(2)  Reflects deduction of the maximum initial sales charge.

29

Appendix

Columbia Acorn USA — Class B Shares

Maximum Sales Charge 0.00%					Initial Hypothetical Investment Amount $10,000.00						Assumed Rate of Return 5%
Year		Cumulative Return Before Fees & Expenses			Annual Expense Ratio			Cumulative Return After Fees & Expenses			Hypothetical Year-End Balance After Fees & Expenses		Annual Fees & Expenses(1)
	1		5.00	%		1.89	%		3.11	%	$	10,311.00	$	191.94
	2		10.25	%		1.89	%		6.32	%	$	10,631.67	$	197.91
	3		15.76	%		1.89	%		9.62	%	$	10,962.32	$	204.06
	4		21.55	%		1.89	%		13.03	%	$	11,303.25	$	210.41
	5		27.63	%		1.89	%		16.55	%	$	11,654.78	$	216.95
	6		34.01	%		1.89	%		20.17	%	$	12,017.24	$	223.70
	7		40.71	%		1.89	%		23.91	%	$	12,390.98	$	230.66
	8		47.75	%		1.89	%		27.76	%	$	12,776.34	$	237.83
	9		55.13	%		1.30	%		32.49	%	$	13,249.06	$	169.17
	10		62.89	%		1.30	%		37.39	%	$	13,739.27	$	175.42
Total Gain After Fees and Expenses												3,739.27
Total Annual Fees and Expenses													$	2,058.05

(1)  Annual Fees and Expenses are calculated based on the average between the beginning and ending balance for each year. All information is calculated on an annual compounding basis.

30

Appendix

Columbia Acorn USA — Class C Shares

Maximum Sales Charge 0.00%					Initial Hypothetical Investment Amount $10,000.00						Assumed Rate of Return 5%
Year		Cumulative Return Before Fees & Expenses			Annual Expense Ratio			Cumulative Return After Fees & Expenses			Hypothetical Year-End Balance After Fees & Expenses		Annual Fees & Expenses(1)
	1		5.00	%		2.09	%		2.91	%	$	10,291.00	$	212.04
	2		10.25	%		2.09	%		5.90	%	$	10,590.47	$	218.21
	3		15.76	%		2.09	%		8.99	%	$	10,898.65	$	224.56
	4		21.55	%		2.09	%		12.16	%	$	11,215.80	$	231.10
	5		27.63	%		2.09	%		15.42	%	$	11,542.18	$	237.82
	6		34.01	%		2.09	%		18.78	%	$	11,878.06	$	244.74
	7		40.71	%		2.09	%		22.24	%	$	12,223.71	$	251.86
	8		47.75	%		2.09	%		25.79	%	$	12,579.42	$	259.19
	9		55.13	%		2.09	%		29.45	%	$	12,945.48	$	266.74
	10		62.89	%		2.09	%		33.22	%	$	13,322.19	$	274.50
Total Gain After Fees and Expenses											$	3,322.19
Total Annual Fees and Expenses													$	2,420.76

(1)  Annual Fees and Expenses are calculated based on the average between the beginning and ending balance for each year. All information is calculated on an annual compounding basis.

31

FOR MORE INFORMATION

Additional information about the Fund's investments is available in the Fund's semiannual and annual reports to shareholders. The annual report contains a discussion of the market conditions and investment strategies that significantly affected the Fund's performance during its last fiscal year.

You may wish to read the SAI for more information on the Fund and the securities in which it invests. The SAI is incorporated into this prospectus by reference, which means that it is considered to be part of this prospectus.

You can get free copies of annual and semiannual reports and the SAI, request other information and discuss your questions about the Fund by visiting www.columbiafunds.com or by writing or calling the Fund's transfer agent at:

Columbia Management Services, Inc.
P.O. Box 8081
Boston, MA 02266-8081
1-800-345-6611

Text-only versions of all Fund documents can be viewed online or downloaded from the EDGAR database on the Securities and Exchange Commission internet site at www.sec.gov.

You can review and copy information about the Fund, including the SAI by visiting the following location, and you can obtain copies upon payment of a duplicating fee, by electronic request at the e-mail address publicinfo@sec.gov or by writing the:

Public Reference Room
Securities and Exchange Commission
Washington, DC 20549-0102

Information on the operation of the Public Reference Room may be obtained by calling 1-202-942-8090.

Investment Company Act file number:
Columbia Acorn Trust: 811-01829
•  Columbia Acorn USA

©2007 Columbia Management Distributors, Inc.
One Financial Center, Boston, MA 02111-2621
800.426.3750 www.columbiafunds.com

INT-36/130215-0507

Columbia^SM

Acorn USA^®  Prospectus, May 1, 2007

Class Z Shares

Advised by Columbia Wanger Asset Management, L.P.

TABLE OF CONTENTS

THE FUND	2
Investment Goal	2
Principal Investment Strategies	2
Principal Investment Risks	2
Portfolio Holdings Disclosure	3
Performance History	3
Your Expenses	5
YOUR ACCOUNT	7
How to Buy Shares	7
Eligible Investors	8
Sales Charges (Commissions)	10
How to Exchange Shares	10
How to Sell Shares	11
Fund Policy on Trading of Fund Shares	12
Financial Intermediary Payments	13
Other Information About Your Account	14
BOARD OF TRUSTEES	17
MANAGING THE FUND	17
Investment Adviser	17
Portfolio Manager	18
Legal Proceedings	18
OTHER INVESTMENT STRATEGIES AND RISKS	20
The Information Edge	20
Long-Term Investing	20
Derivative Strategies	20
Temporary Defensive Strategies	21
FINANCIAL HIGHLIGHTS	22
APPENDIX	23

Only eligible investors may purchase Class Z shares. See "Your Account — Eligible Investors" for more information.

Although these securities have been registered with the Securities and Exchange Commission, the Commission has not approved or disapproved any shares offered in this prospectus or determined whether this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Acorn USA^® is a trademark owned and registered by Columbia Acorn Trust, Columbia, Columbia Management^® and Columbia Management Services, Inc. are service marks owned and/or registered by Bank of America

The Fund

INVESTMENT GOAL

Columbia Acorn USA (Acorn USA^®) seeks to provide long-term growth of capital.

PRINCIPAL INVESTMENT STRATEGIES

Acorn USA generally invests in stocks of small- and medium-sized U.S. companies. The Fund generally invests in the stocks of U.S. companies with market capitalizations of less than $5 billion at the time of initial purchase. As long as a stock continues to meet the Fund's other investment criteria, the Fund may choose to hold a stock even if the issuing company's capitalization grows beyond a $5 billion capitalization.

Acorn USA believes that these smaller companies, which are not as well known by financial analysts, may offer higher return potential than the stocks of larger companies.

Acorn USA typically looks for companies with:

•  A strong business franchise that offers growth potential.

•  Products and services that give the company a competitive advantage.

•  A stock price the Fund's investment adviser believes is reasonable relative to the assets and earning power of the company.

Acorn USA generally invests substantially all of its assets in U.S. companies, and, under normal circumstances, will invest at least 80% of its net assets (plus any borrowings for investment purposes) in U.S. companies.

Additional strategies that are not principal investment strategies and the risks associated with them are described later in this prospectus under "Other Investment Strategies and Risks."

PRINCIPAL INVESTMENT RISKS

The principal risks of investing in the Fund are described below. There are many circumstances (including additional risks that are not described here) that could prevent the Fund from achieving its investment goal. You may lose money by investing in the Fund.

Management risk means that the adviser's investment decisions might produce losses or cause the Fund to underperform when compared to other funds with a similar investment goal. Market risk means that security prices in a market, sector or industry may fall, reducing the value of your investment. Because of management and market risk, there is no guarantee that the Fund will achieve its investment goal or perform favorably among comparable funds.

Since the Fund purchases equity securities, it is subject to equity risk. This is the risk that stock prices will fall over short or extended periods of time. Although the stock market historically has outperformed other asset classes over the long term, the stock market tends to move in cycles. Individual stock prices may fluctuate drastically from day-to-day and may underperform other asset classes over an extended period of time. Individual companies may report poor results or be negatively affected by industry and/or economic trends and developments. The prices of securities issued by such companies may suffer a decline in response. These price movements may result from factors affecting individual companies, industries or the securities market as a whole.

Sector risk is inherent in the Fund's investment strategy. Companies that are in different but closely related industries are sometimes described as being in the same broad economic sector. The values of stocks of different companies in a market sector may be similarly affected by particular economic or market events. Although the Fund does not intend to focus on any particular sector, at times the Fund may have a large portion of its assets invested in a particular sector.

2

The Fund

Because the Fund invests in stocks, the price of its shares — its net asset value (NAV) per share — fluctuates daily in response to changes in the market value of stocks.

Small- or mid-cap companies may be more susceptible to market downturns, and their prices could be more volatile than large-cap companies. These companies are more likely than larger companies to have limited product lines, operating histories, markets or financial resources. They may depend heavily on a small management team and may trade less frequently, may trade in smaller volumes and may fluctuate more sharply in price than stocks of larger companies. In addition, such companies may not be widely followed by the investment community, which can lower the demand for their stocks.

An investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PORTFOLIO HOLDINGS DISCLOSURE

A description of the Fund's policies and procedures with respect to the disclosure of its portfolio securities is available in the Fund's Statement of Additional Information (SAI), which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611.

The Fund posts its complete portfolio holdings as of month-end at www.columbiafunds.com approximately 30-40 calendar days after such month-end. Additionally, the Fund discloses its top 15 month-end portfolio holdings at www.columbiafunds.com on or about 15 calendar days following such month-end.

Once posted, the above information will remain available on the website until at least the date on which the Fund files a Form N-CSR or Form N-Q for the period that includes the date as of which the information is current.

PERFORMANCE HISTORY

The bar chart below shows the Fund's calendar-year total returns (before taxes) for its Class Z shares. The performance table following the bar chart shows how the Fund's average annual total returns for Class Z shares compare with a broad measure of market performance for one year, five years and ten years. The chart and table are intended to illustrate some of the risks of investing in the Fund by showing changes in the Fund's performance from year to year. All returns include the reinvestment of dividends and distributions. As with all mutual funds, past performance (before and after taxes) does not predict the Fund's future performance.

UNDERSTANDING PERFORMANCE

Calendar Year Total Returns show the Fund's Class Z share performance for each completed calendar year since the Fund commenced operations. They include the effects of Fund expenses.

Average Annual Total Returns are a measure of the Fund's Class Z average performance over the past one year, five years and life of the share class. They include the effects of Fund expenses.

The Fund's returns are compared to the Russell 2000^® Index (Russell 2000^®). The Russell 2000^® is a market-weighted index of the 2000 smallest companies of the 3000 largest U.S. companies based on market-capitalization. All third-party trademarks are the property of their owners. Unlike the Fund, an index is not an investment, does not incur fees, expenses or taxes, and is not professionally managed.

3

The Fund

Calendar Year Total Returns (Class Z)

For the periods shown in bar chart:
Best quarter: 2nd quarter 2003, +23.22%
Worst quarter: 3rd quarter 2002, -21.21%

After tax returns are calculated using the highest historical individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on each investor's own tax situation and may differ from those shown. After-tax returns may not be relevant to investors who hold Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Average Annual Total Returns — for periods ended December 31, 2006

Share Class	1 Year		5 Years		10 Years
Class Z (%)
Return Before Taxes		8.28		12.09		12.70
Return After Taxes on Distributions		7.94		11.83		12.00
Return After Taxes on Distributions and Sale of Fund Shares		5.83		10.57		11.05
Index
Russell 2000® (%)		18.37		11.39		9.44

4

The Fund

YOUR EXPENSES

Expenses are one of several factors to consider before you invest in a mutual fund. The tables below describe the fees and expenses you may pay when you buy, hold and sell shares of the Fund.

UNDERSTANDING EXPENSES

Annual Fund Operating Expenses are paid by the Fund. They include management and administration fees and other expenses that generally include, but are not limited to, transfer agency, custody, and legal fees as well as costs related to state registration and printing of Fund documents. The specific fees and expenses that make up the Fund's other expenses will vary from time to time and may include fees or expenses not described here. The Fund will likely incur portfolio transaction costs that are in addition to the total annual fund operating expenses disclosed in the fee table. These transaction costs are made up of all costs that are associated with trading securities for the Fund's portfolio and include, but are not limited to, brokerage commissions and market spreads, as well as potential changes to the price of a security due to the Fund's efforts to purchase or sell it. While certain elements of transaction costs are read ily identifiable and quantifiable, other elements that can make up a significant amount of the Fund's transaction costs are not. Higher transaction costs reduce the Fund's returns.

Shareholder Fees (commissions paid directly from your investment)

Maximum sales charge (load) on purchases (%) (as a percentage of the offering price)	None
Maximum deferred sales charge (load) on redemptions (%) (as a percentage of the lesser of purchase price or redemption price)	None
Redemption fee (%) (as a percentage of amount redeemed, if applicable)	None(1)

(1)  There is a $7.50 charge for wiring sale proceeds to your bank.

Annual Fund Operating Expenses (deducted directly from Fund assets)

Management fees(1) (%)	0.86
Distribution and service (12b-1) fees (%)	None
Other expenses(2) (%)	0.15
Total annual fund operating expenses (%)	1.01

(1)  The Fund pays an investment advisory fee of 0.86%. The Fund and its adviser have implemented a breakpoint schedule for the Fund's investment advisory fees. The investment advisory fee rates charged to the Fund will decline as Fund assets grow and will continue to be based on a percentage of the Fund's average daily assets. The annual fee schedule for the Fund is as follows: 0.94% for assets up to $200 million; 0.89% for assets in excess of $200 million and up to $500 million; 0.84% for assets in excess of $500 million and up to $2 billion; and 0.80% for assets in excess of $2 billion and up to $3 billion; and 0.70% for assets in excess of $3 billion. In addition to the management fee, the Fund and the other funds of Columbia Acorn Trust (the "Trust") pay the adviser an administrative fee based on the average daily aggregate net assets of the Trust at the following annual rates: 0.05% of net assets up to $8 billion ; 0.04% of the next $8 billion; and 0.03% of net assets in excess of $16 billion. Based on the Trust's average daily net assets as of December 31, 2006, the administrative fee would be at a rate of 0.04% and is included in "Other expenses."

(2)  "Other expenses" have been restated to reflect contractual changes to the transfer agency fees paid by the Fund.

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The Fund

Example Expenses help you compare the cost of investing in the Fund to the cost of investing in other mutual funds. It uses the following hypothetical conditions:

•  $10,000 initial investment†

•  5% total return for each year

•  Fund operating expenses remain the same

•  Reinvestment of all dividends and distributions

†  For example only, since the minimum initial investment in the Fund is $75,000, subject to certain exceptions described in the section "Eligible Investors" on page 8.

Example Expenses for a $10,000 investment (your actual costs may be higher or lower)

1 Year		3 Years		5 Years		10 Years
$	103	$	322	$	558	$	1,236

See the Appendix for additional hypothetical investment and expense information.

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HOW TO BUY SHARES

If you are an eligible investor (described on page 8), when the Fund receives your purchase request in "good form," your shares will be bought at the next calculated price. "Good form" means the Fund's transfer agent has all information and documentation it deems necessary to effect your order. For example "good form" may mean that you have properly placed your order with Columbia Management Services, Inc. or your financial advisor or the Fund's transfer agent has received your completed application, including all necessary signatures. The Fund reserves the right to refuse a purchase order for any reason, including if the Fund believes that doing so would be in the best interest of the Fund and its shareholders. The USA PATRIOT Act may require us to obtain certain personal information from you that we will use to verify your identity. If you do not provide the information, we may not be able to open your account. If we are unabl e to verify your customer information, we reserve the right to close your account or take such other steps as we deem reasonable.

You or your financial advisor may acquire shares of the Fund for your account by exchanging shares you own in a different fund distributed by Columbia Management Distributors, Inc. for shares of the same class or Class A of the Fund at no additional cost. To exchange by telephone, call 1-800-422-3737. Please see "How to Exchange Shares" for more information.

Outlined below are the various options for buying shares:

Method	Instructions
Through your financial advisor	Your financial advisor can help you establish your account and buy Fund shares on your behalf. To receive the current trading day's price, your financial advisor must receive your request prior to the close of regular trading on the New York Stock Exchange (NYSE), usually 4:00 p.m. Eastern time. Your financial advisor may charge you fees for executing the purchase for you.
By check (new account)	For new accounts, send a completed application and check made payable to the Fund to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By check (existing account)	For existing accounts, fill out and return the additional investment stub included in your account statement, or send a letter of instruction including the name, Fund share class and account number with a check made payable to the Fund to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By exchange	You may acquire Fund shares for your account by exchanging shares you own in a different fund distributed by Columbia Management Distributors, Inc. for shares of the same class or Class A shares of the Fund at no additional cost. To exchange by telephone, call 1-800-422-3737. Please see "How to Exchange Shares" for more information.
By wire	You may purchase Fund shares by wiring money from your bank account to your Fund account. To wire funds to your Fund account, call 1-800-422-3737 for wiring instructions.
By electronic funds transfer	You may purchase Fund shares by electronically transferring money from your bank account to your Fund account by calling 1-800-422-3737. An electronic funds transfer may take up to two business days to settle and must be considered in "good form." You must set up this feature prior to your telephone request. Be sure to complete the appropriate section of the application for this feature.
Automatic investment plan	You may make monthly or quarterly investments ($50 minimum) automatically from your bank account to your Fund account. You may select a pre-authorized amount to be sent via electronic funds transfer. Be sure to complete the appropriate section of the application for this feature.
Automated dollar cost averaging	You may purchase Fund shares for your account by exchanging $100 or more each month from another fund for shares of the same class of the Fund at no additional cost. Exchanges will continue so long as your fund balance is sufficient to complete the transfers. You may terminate your program or change the amount of the exchange (subject to the $100 minimum) by calling 1-800-345-6611. Be sure to complete the appropriate section of the account application for this feature.

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Method	Instructions
By dividend diversification	You may automatically invest dividends distributed by another fund into the same class of shares of the Fund at no additional sales charge. There may be an additional sales charge if automatically investing dividends from a money market fund. To invest your dividends in the Fund, call 1-800-345-6611.
Through the internet	You may purchase Fund shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet purchases. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

ELIGIBLE INVESTORS

Only certain eligible investors may purchase Class Z shares of the Fund (Eligible Investor), directly or by exchange. Please read the following section for a more detailed description of the eligibility requirements. The Eligible Investors described below are subject to different minimum initial investment requirements.

Eligibility for certain waivers, exemptions or share classes by new or existing investors may not be readily available or accessible through all intermediaries or all types of accounts offered by a broker-dealer, bank, third-party administrator or other financial institution (each commonly referred to as an "intermediary"). Accessibility of these waivers through a particular intermediary also may change at any time. If you believe you are eligible to purchase shares under a specific exemption, but are not permitted by your intermediary to do so, please contact your intermediary. You may be asked to provide information, including account statements and other records, regarding your eligibility.

Eligible Investors and their applicable investment minimums are as follows:

No minimum initial investment

•  Any trustee or director (or family member) of Columbia Acorn Trust;

•  Any employee (or family member) of Columbia Wanger Asset Management, L.P.; or

•  Any group retirement plan, holding Fund shares in an omnibus manner, for which an intermediary or other entity provides services and is not compensated by the Funds for those services, other than payments for shareholder servicing or sub-accounting performed in place of the transfer agent.

$75,000 minimum initial investment (by purchase, exchange or transfer)

•  Any individual retirement account of an Eligible Investor;

•  Any group retirement plan, not holding Fund shares in an omnibus manner, for which an intermediary or other entity provides services and is not compensated by the Fund for those services, other than compensation for shareholder servicing or sub-accounting performed in place of the transfer agent;

•  Any shareholder (as well as any family member of a shareholder or person listed on an account registration for any account of the shareholder) of a fund distributed by Columbia Management Distributors, Inc. (CMD) (i) who holds Class Z shares; (ii) who holds shares issued upon conversion of Primary A shares held prior to August 22, 2005; (iii) who holds Class A shares that were obtained by exchange of Class Z shares; or (iv) who holds no-load shares issued upon the merger of a fund distributed by CMD;

•  Any trustee or director (or family member of a trustee or director) of any fund distributed by CMD (other than the Columbia Acorn Funds);

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•  Any employee (or family member of an employee) of Bank of America Corporation or a subsidiary (other than Columbia Wanger Asset Management L.P.);

•  Any investor participating in an account offered by an intermediary or other entity that provides services to such an account, is paid an asset-based fee by the investor and is not compensated by the Funds for those services, other than payments for shareholder servicing or sub-accounting performed in place of the Fund's transfer agent (each investor purchasing through an intermediary must independently satisfy the $75,000 minimum investment requirement);

•  Any client of Bank of America Corporation or a subsidiary purchasing through an asset management company, trust, fiduciary, retirement plan administration or similar arrangement with Bank of America Corporation or the subsidiary;

•  Any person investing all or part of the proceeds of a distribution, rollover or transfer of assets into a Columbia Management Individual Retirement Account from any deferred compensation plan which was a shareholder of any of the funds of Columbia Acorn Trust (formerly named Liberty Acorn Trust) on September 29, 2000, in which the investor was a participant and through which the investor invested in one or more of the funds of Columbia Acorn Trust immediately prior to the distribution, transferor rollover;

•  Any investor purchasing through a Columbia Management state tuition plan organized under Section 529 of the Internal Revenue Code;

•  Any institutional investor which is a corporation, partnership, trust, foundation, endowment, institution, government entity, or similar organization; which meets the respective qualifications for an accredited investor, as defined under the Securities Act of 1933; or

•  Certain financial institutions and intermediaries, such as insurance companies, trust companies, banks, endowments, investment companies or foundations, purchasing shares for its own account, including Bank of America Corporation, its affiliates, or subsidiaries.

The investment minimum is applied at the class level. For group retirement plans, the investment minimum is determined based on the amount of the plan's investment rather than that of its individual participants. The Fund may establish exclusions from the investment minimum from time to time that it deems appropriate and consistent with the interests of shareholders. Please see the SAI for details on these exclusions.

The Fund reserves the right to change the criteria for eligible investors and the investment minimums. For accounts opened prior to December 15, 2003, no minimum investment applies to accounts participating in the automatic investment plan; however, each investment requires a $50 minimum purchase. The Fund also reserves the right to refuse a purchase order for any reason, including if it believes that doing so would be in the best interest of the Fund and its shareholders. Finally, pursuant to the Trust's Agreement and Declaration of Trust, the Fund reserves the right to redeem your shares if your account falls below the minimum investment requirements.

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SALES CHARGES (COMMISSIONS)

Your purchases of Class Z shares are at net asset value, which is the value of a Class Z share excluding any sales charge. Class Z shares are not subject to an initial sales charge when purchased, or a contingent deferred sales charge when sold.

CHOOSING A SHARE CLASS

The Fund offers one class of shares in this prospectus — Class Z.

The Fund also offers three additional classes of shares — Class A, B and C shares are available through a separate prospectus. Each other share class has its own sales charge and expense structure.

Broker-dealers, investment advisers or financial planners selling mutual fund shares may offer their clients more than one class of shares in a fund with different pricing options. This allows you and your financial advisor to choose among different types of sales charges and different levels of ongoing operating expenses, depending on the investment programs your financial advisor offers. Investors should consider carefully any separate transactions and other fees charged by these programs in connection with investing in any available share class before selecting a share class.

Determining which share class is best for you depends on the dollar amount you are investing and the number of years for which you are willing to invest. Based on your personal situation, your financial advisor can help you decide which class of shares makes the most sense for you. In general, anyone who is eligible to purchase Class Z shares, which do not incur Rule 12b-1 fees or sales charges, should do so in preference over other classes.

If you purchase Class Z shares of the Fund through certain intermediaries, they may charge a fee for their services. They may also place limits on your ability to use services the Fund offers. There are no sales charges or limitations if you purchase shares directly from the Fund, except as described in this prospectus.

If an intermediary is an agent or designee of the Fund, orders are processed at the net asset value next calculated after the intermediary receives the order. The intermediary must segregate any orders it receives after the close of regular trading on the NYSE and transmit those orders separately for execution at the net asset value next determined.

HOW TO EXCHANGE SHARES

You may exchange your shares for Class Z or Class A (only if Class Z is not offered) shares of another fund distributed by CMD at net asset value. Unless your account is part of a tax-deferred retirement plan, an exchange is a taxable event, and you may realize a gain or a loss for tax purposes. The Fund may terminate your exchange privilege if the adviser determines that your exchange activity is likely to adversely impact its ability to manage the Fund. See "Fund Policy on Trading of Fund Shares" for the Fund's policy. To exchange by telephone, call 1-800-422-3737. Please have your account and taxpayer identification numbers available when calling.

You also may exchange your shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet exchanges. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

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HOW TO SELL SHARES

You may sell shares of the Fund on any regular business day that the NYSE is open.

When the Fund receives your sales request in "good form," shares will be sold at the next calculated net asset value. "Good form" means that the Fund's transfer agent has all information and documentation it deems necessary to effect your order. For example, when selling shares by letter of instruction, "good form" also means (i) your letter has complete instructions, the proper signatures and Medallion Signature Guarantees, and (ii) any other required documents are attached. For additional documents required for sales by corporations, agents, fiduciaries, surviving joint owners and other legal entities, please call 1-800-345-6611. Retirement plan accounts have special requirements; please call 1-800-799-7526 for more information.

The Fund will generally send proceeds from the sale to you within seven days (usually on the next business day after your request is received in "good form"). However, if you purchased your shares by check, the Fund may delay sending the proceeds from the sale of your shares for up to 10 days after your purchase to protect against checks that are returned. No interest will be paid on uncashed redemption checks. Redemption proceeds may be paid in securities, rather than cash, under certain circumstances. For more information, see the paragraph "Non-Cash Redemptions" under the section "How to Sell Shares" in the SAI.

During any 90-day period for any one shareholder, the Fund is obligated to redeem shares solely in cash up to the lesser of $250,000 or 1% of the Fund's net assets. Redemptions in excess of these limits will normally be paid in cash, but may be paid wholly or partly by an in-kind distribution of securities.

Outlined below are the various options for selling shares:

Method	Instructions
Through your financial advisor	You may call your financial advisor to place your sell order. To receive the current trading day's price, your financial advisor must receive your request prior to the close of regular trading on the NYSE, usually 4:00 p.m. Eastern time. Your financial advisor may charge you fees for executing a redemption for you.
By exchange	You or your financial advisor may sell Fund shares by exchanging from the Fund into Class Z shares or Class A shares (only if Class Z is not offered) of another fund distributed by Columbia Management Distributors, Inc. at no additional cost. To exchange by telephone, call 1-800-422-3737.
By telephone	You or your financial advisor may sell Fund shares by telephone and request that a check be sent to your address of record by calling 1-800-422-3737, unless you have notified the Fund of an address change within the previous 30 days. The dollar limit for telephone sales is $100,000 in a 30-day period. You do not need to set up this feature in advance of your call. Certain restrictions apply to retirement accounts. For details, call 1-800-799-7526.
By mail	You may send a signed letter of instruction to the address below. In your letter of instruction, note the Fund's name, share class, account number, and the dollar value or number of shares you wish to sell. All account owners must sign the letter. Signatures must be guaranteed by either a bank, a member firm of a national stock exchange or another eligible guarantor that participates in the Medallion Signature Guarantee Program for amounts over $100,000 or for alternate payee or mailing instructions. Additional documentation is required for sales by corporations, agents, fiduciaries, surviving joint owners and individual retirement account owners. For details, call 1-800-345-6611. Mail your letter of instruction to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By wire	You may sell Fund shares and request that the proceeds be wired to your bank. You must set up this feature prior to your request. Be sure to complete the appropriate section of the account application for this feature. Generally, the value of your redemption must be at least equal to $500 in order to have the sale proceeds wired to your bank. There is a $7.50 charge for wiring sale proceeds to your bank. (The transfer agent may waive this fee for omnibus and nominee accounts.) Your bank may charge additional fees for such wire transfer.

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Method	Instructions
By systematic withdrawal plan	You may automatically sell a specified dollar amount or percentage of your account on a monthly, quarterly or semiannual basis and have the proceeds sent to you if your account balance is at least $5,000. The $5,000 minimum account balance requirement is waived for wrap accounts. All dividend and capital gains distributions must be reinvested. Be sure to complete the appropriate section of the account application for this feature.
By electronic funds transfer	You may sell Fund shares and request that the proceeds be electronically transferred to your bank. Proceeds may take up to two business days to be received by your bank. You must set up this feature prior to your request. Be sure to complete the appropriate section of the account application for this feature.
Through the internet	You may sell Fund shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet redemptions. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

FUND POLICY ON TRADING OF FUND SHARES

The interests of the Fund's long-term shareholders may be adversely affected by certain short-term trading activity by Fund shareholders. Such short-term trading activity, when excessive, has the potential to interfere with efficient portfolio management, generate transaction and other costs, dilute the value of Fund shares held by long-term shareholders and have other adverse effects on the Fund. This type of excessive short-term trading activity is referred to herein as "market timing." For purposes of this section, "Columbia Funds" are the Columbia, Columbia Acorn Trust and Wanger Advisors Trust families of mutual funds. The Columbia Funds are not intended as vehicles for market timing. The Board of Trustees of the Fund has adopted the policies and procedures set forth below with respect to frequent trading of the Fund's shares.

The Fund, directly and through its agents, takes various steps designed to deter and curtail market timing. For example, if the Fund detects that any shareholder has conducted two "round trips" (as defined below) in the Fund in any 28-day period, except as noted below with respect to orders received through omnibus accounts, the Fund will reject the shareholder's future purchase orders, including exchange purchase orders, involving any Columbia fund (other than a money market fund). In addition, if the Fund determines that any person, group or account has engaged in any type of market timing activity (independent of the two-round-trip limit), the Fund may, in its discretion, reject future purchase orders by the person, group or account, including exchange purchase orders, involving the same or any other Columbia fund, and also retains the right to modify these market timing policies at any time without prior notice.

The rights of shareholders to redeem shares of the Fund are not affected by any of the limits mentioned above. However, certain Funds (other than the Fund) impose a redemption fee on the proceeds of fund shares that are redeemed or exchanged within 60 days of their purchase.

For these purposes, a "round trip" is a purchase by any means into a Columbia fund followed by a redemption, of any amount, by any means out of the same Columbia fund. Under this definition, an exchange into the Fund followed by an exchange out of the Fund is treated as a single round trip. Also for these purposes, where known, accounts under common ownership or control generally will be counted together. Accounts maintained or managed by a common intermediary, such as an adviser, selling agent or trust department, generally will not be considered to be under common ownership or control.

Purchases, redemptions and exchanges made through the Columbia Funds' Automatic Investment Plan, Systematic Withdrawal Plan or similar automated plans are not subject to the two-round-trip limit. Purchases, redemptions and exchanges made by Columbia Thermostat Fund are also not subject to the two round-trip limit.

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The two-round-trip limit may be modified for, or may not be applied to, accounts held by certain retirement plans to conform to plan limits, considerations relating to the Employee Retirement Income Security Act of 1974 or regulations of the Department of Labor, and for certain asset allocation or wrap programs.

The practices and policies described above are intended to deter and curtail market timing in the Fund. However, there can be no assurance that these policies, individually or collectively, will be totally effective in this regard because of various factors. In particular, a substantial portion of purchase, redemption and exchange orders are received through omnibus accounts. Omnibus accounts, in which shares are held in the name of an intermediary on behalf of multiple beneficial owners, are a common form of holding shares among financial intermediaries and retirement plans. The Fund typically is not able to identify trading by a particular beneficial owner through an omnibus account, which may make it difficult or impossible to determine if a particular account is engaged in market timing. Consequently, there is the risk that the Fund may not be able to identify, deter or curtail certain market timing that occurs in the Fund, which may result in certain shareholders being able to market time the Fund while the shareholders in the Fund bear the burden of such activities.

Certain financial intermediaries, including certain retirement plan service providers whose clients include, among others, various retirement plans sponsored by Bank of America and its affiliates for the benefit of its employees (the "Bank of America retirement plan service providers"), have different policies regarding monitoring and restricting market timing in the underlying beneficial owner accounts that they maintain through an omnibus account that may be more or less restrictive than the Fund practices discussed above. In particular, the Bank of America retirement plan service providers permit the reinstatement of future purchase orders for shares of the Fund following various suspension periods. If an intermediary does not enforce the Fund's policy, the intermediary must either provide data transparency to Columbia Management or Columbia Management must determine that the intermediary's policy taken in its entirety provid es protections to Fund shareholders that are generally commensurate with the Fund's policy.

The Fund seeks to act in a manner that it believes is consistent with the best interests of Fund shareholders in making any judgments regarding market timing. Neither the Fund nor its agents shall be held liable for any loss resulting from rejected purchase orders or exchanges.

FINANCIAL INTERMEDIARY PAYMENTS

The Fund's distributor, investment adviser or their affiliates may make payments, from their own resources, to certain financial intermediaries, including other Bank of America affiliates, for marketing support services. For purposes of this section the term "financial intermediary" includes any broker, dealer, bank, bank trust department, registered investment adviser, financial planner, retirement plan or other third-party administrator and any other institution having a selling, services or any similar agreement with the Fund's distributor, investment adviser or one of their affiliates. These payments are generally based upon one or more of the following factors: average net assets of the mutual funds distributed by the Fund's distributor attributable to that financial intermediary, gross sales of the mutual funds distributed by the Fund's distributor attributable to that financial intermediary, reimbursement of ticket charge s (fees that a financial intermediary firm charges its representatives for effecting transactions in fund shares) or a negotiated lump sum payment.

While the financial arrangements may vary for each financial intermediary, the payments to any one financial intermediary are generally expected to be between 0.05% and 0.45% on an annual basis for payments based on

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average net assets of the Fund attributable to the financial intermediary, and between 0.10% and 0.25% on an annual basis for firms receiving a payment based on gross sales of the Fund attributable to the financial intermediary. The Fund's distributor, investment adviser or their affiliates may make payments in materially larger amounts or on a basis materially different from those described above when dealing with other affiliates of Bank of America. Such increased payments to the other Bank of America affiliate may enable the other Bank of America affiliate to offset credits that it may provide to its customers in order to avoid having such customers pay fees to multiple Bank of America entities in connection with the customer's investment in the Fund.

Payments also may be made to certain financial intermediaries, including other Bank of America affiliates, that provide investor services to retirement plans and other investment programs to compensate financial intermediaries for services they provide to such programs, including, but not limited to, sub-accounting, sub-transfer agency, similar shareholder or participant recordkeeping, shareholder or participant reporting, or shareholder or participant transaction processing. These payments for investor servicing support vary by financial intermediary but generally are not expected, with certain limited exceptions, to exceed 0.45% of the total Fund assets for Class Z shares in the program on an annual basis.

The Trust's Board of Trustees has authorized the Fund to pay to any intermediary up to 0.05% of the average aggregate value of Fund shares in the intermediary's program on an annual basis for providing investor services. Charges of an intermediary in excess of that paid by the Fund will be borne by the Fund's distributor or its affiliates.

The Fund's distributor, investment adviser or their affiliates may make other payments or allow promotional incentives to financial intermediaries to the extent permitted by the rules of the Securities and Exchange Commission, the National Association of Securities Dealers and by other applicable laws and regulations.

Amounts paid by the Fund's distributor, investment adviser or their affiliates are paid out of the distributor's, investment adviser's or their affiliates' own resources and do not increase the amount paid by you or the Fund. You can find further details about the payments made by the Fund's distributor, investment adviser or their affiliates and the services provided by financial intermediaries as well as a list of the financial intermediaries to which the Fund's distributor, investment adviser or their affiliates have agreed to make marketing support payments in the Fund's SAI, which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611. Your financial intermediary may charge you fees or commissions in addition to those disclosed in this prospectus. You can ask y our financial intermediary for information about any payments it receives from the Fund's distributor, investment adviser and their affiliates and any services your financial intermediary provides, as well as fees and/or commissions it charges. In addition, depending on the financial arrangement in place at any particular time, a financial intermediary and its financial consultants also may have a financial incentive for recommending a particular fund or share class over others. You should consult with your financial adviser and review carefully any disclosure by the financial intermediary as to compensation received by your financial adviser.

OTHER INFORMATION ABOUT YOUR ACCOUNT

How the Fund's Share Price is Determined The Fund's Class Z share price is based on its net asset value. The net asset value is determined at the close of regular trading on the NYSE, usually 4:00 p.m. Eastern time, on each business day that the NYSE is open for trading (typically Monday through Friday). Net asset value is not determined on days on which the NYSE is closed for trading.

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When you request a transaction, it will be processed at the net asset value per share next determined after your request is received in "good form" by the distributor. In most cases, in order to receive that day's price, the Fund must receive your order before that day's transactions are processed. If you request a transaction through your financial advisor, your financial advisor must receive your order by the close of trading on the NYSE to receive that day's price.

The Fund determines its net asset value for its Class Z shares by dividing total net assets attributable to Class Z shares by the number of outstanding Class Z shares. In determining the net asset value, the Fund must determine the value of each security in its portfolio at the close of each trading day. Securities for which market quotations are available are valued each day at the current market value. However, where market quotations are unavailable, or when the adviser believes that subsequent events have made them unreliable, the Fund may use other data to determine the fair value of the securities.

The Fund has retained an independent statistical fair value pricing service to assist in the fair valuation process for securities principally traded in a foreign market in order to adjust for possible changes in value that may occur between the close of the foreign exchange and the time at which Fund shares are priced. The use of an independent fair value pricing service is intended to and may decrease the opportunities for time zone arbitrage transactions. There can be no assurance that the use of an independent fair value pricing service will successfully decrease arbitrage opportunities. If a security is valued at a "fair value," that value may be different from the last quoted market price for the security.

You can find the daily prices of some share classes for the Fund in most major daily newspapers under the heading of "Columbia." You can find daily prices for all share classes by visiting www.columbiafunds.com.

Share Certificates Share certificates are not available for Class Z shares.

Dividends, Distributions, and Taxes The Fund has the potential to make the following distributions:

Types of Distributions

Dividends	Represents interest and dividends earned from securities held by the Fund, net of expenses incurred by the Fund.
Capital gains	Represents net long-term capital gains on sales of securities held for more than one year and net short-term capital gains, which are gains on sales of securities held for a one-year period or less.

Distribution Options The Fund distributes any dividends in June and December and any capital gains (including short-term capital gains) at least annually. You can choose one of the options listed in the table below for these distributions when you open your account. To change your distribution option call 1-800-345-6611.

If you do not indicate on your application or at the time your account is established your preference for handling distributions, the Fund will automatically reinvest all distributions in additional shares of the Fund.

UNDERSTANDING FUND DISTRIBUTIONS

The Fund may earn income from the securities it holds. The Fund also may realize capital gains or losses on sales of its securities. The Fund intends to distribute substantially all of its net investment income and capital gains to shareholders each year. As a shareholder, you are entitled to a portion of the Fund's income and capital gains based on the number of shares you own at the time these distributions are declared.

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Distribution Options

Reinvest all distributions in additional shares of the Fund

Reinvest all distributions in shares of another fund

Receive dividends in cash (see options below) and reinvest capital gains

Receive all distributions in cash (with one of the following options):

•  send the check to your address of record

•  send the check to a third-party address

•  transfer the money to your bank via electronic funds transfer

Distributions of $10 or less will automatically be reinvested in additional Fund shares. If you elect to receive distributions by check and the check is returned as undeliverable, all subsequent distributions will be reinvested in additional shares of the Fund.

TaxesUnless you are an entity exempt from income taxes or invest under a retirement account, regardless of whether you receive your distributions in cash or reinvest them in additional Fund shares, all Fund distributions are subject to federal income tax. Depending on where you live, distributions also may be subject to state and local income taxes.

The Fund intends to elect to be treated and to qualify each year as a regulated investment company. A regulated investment company is not subject to tax at the corporate level on income and gains from investments that are distributed to shareholders in accordance with applicable law. However, the Fund's failure to qualify as a regulated investment company could result in corporate level taxation, and consequently, a reduction in income available for distribution to shareholders.

In general, any distributions of dividends, interest and short-term capital gains (determined by how long the Fund held the investments that generated them) are taxable as ordinary income, unless such dividends are "qualified dividend income" (as defined in the Internal Revenue Code) eligible for a reduced rate of tax. Properly designated distributions of long-term capital gains (determined by how long the Fund held the investments that generated them) are generally taxable as such, regardless of how long you have held your Fund shares. You will be provided with information each year regarding the amount of ordinary income and capital gains distributed to you for the previous year and any portion of your distribution which is exempt from state and local taxes. Long-term capital gain rates have been reduced — in general, to 15% with lower rates applying to taxpayers in the 10% and 15% rate brackets — for taxable years b eginning before January 1, 2011. Distributions are taxable to you even if they are paid from income or gains earned by the Fund before you made your investment (and thus were included in the price you paid). Your investment in the Fund may have additional personal tax implications. Please consult your tax advisor about federal, state, local or other applicable tax laws.

In addition to the dividends and capital gains distributions made by the Fund, you may realize a capital gain or loss when selling or exchanging shares of the Fund. Such transactions also may be subject to federal, state and local income tax.

16

Board of Trustees

The Fund is governed by its Board of Trustees. More than 75% of the Fund's Trustees are independent, meaning that they have no affiliation with the adviser or the Funds, apart from their positions as Trustees and the personal investments they may have made as private individuals.

The independent Trustees bring backgrounds in business and the professions and academia to their task of working with the Funds' officers to establish the policies and oversee the activities of the Funds. Among the Trustees' responsibilities are selecting the investment adviser for the Funds; negotiating the advisory agreements; reviewing other contracts; approving investment policies; monitoring Fund operations, performance, and costs; and nominating or selecting new Trustees.

Each Trustee serves until his or her retirement, resignation, death or removal; or otherwise as specified in the Trust's organizational documents. It is expected that every five years the Trustees will call a meeting of shareholders to elect Trustees. A Trustee must retire at the end of the year in which he or she attains the age of 75. Any Trustee may be removed at a shareholders' meeting by a vote representing two-thirds of the net asset value of all shares of the Funds of the Trust. The mailing address for the Trustees and officers is 227 W. Monroe, Suite 3000, Chicago, Illinois 60606.

For more detailed information on the Board of Trustees, please refer to the SAI.

Managing the Fund

INVESTMENT ADVISER

Columbia Wanger Asset Management, L.P. (CWAM), located at 227 West Monroe Street, Suite 3000, Chicago, Illinois 60606, is the Fund's investment adviser and is responsible for the Fund's management, subject to the oversight of the Fund's Board of Trustees. CWAM and its predecessor have managed mutual funds, including the Fund, since 1992. In its duties as investment adviser, CWAM runs the Fund's day-to-day business, including making investment decisions and placing all orders for the purchase and sale of the Fund's portfolio securities.

CWAM was previously named Liberty Wanger Asset Management, L.P. and its predecessor was named Wanger Asset Management, L.P. (WAM). CWAM is a wholly owned subsidiary of Columbia Management Group, LLC, which is an indirect wholly owned subsidiary of Bank of America Corporation. As of December 31, 2006, CWAM managed more than $32.9 billion in assets.

CWAM's advisory fee for managing the Fund in 2006 was 0.86% of the Fund's average daily net assets. CWAM also received an administrative fee from the Fund in 2006 of 0.04% of the Fund's average daily net assets. A discussion of the factors considered by the Fund's Board of Trustees in approving the Fund's investment advisory contract is included in the Fund's annual report to shareholders for the period ended December 31, 2006.

17

Managing the Fund

PORTFOLIO MANAGER

CWAM uses a team to assist the lead portfolio manager in managing the Fund. Team members share responsibility for providing ideas, information and knowledge in managing the Fund, and each team member has one or more particular areas of expertise. The portfolio manager is responsible for making daily investment decisions and utilizing the management team's input and advice when making buy and sell determinations.

Robert A. MohnLead portfolio manager

Robert Mohn is a vice president of the Trust. He has been a member of the domestic analytical team at CWAM and its predecessor since August 1992. He has managed Columbia Acorn USA since its inception in 1996, co-managed Columbia Acorn Fund since May 2003, and also manages Wanger U.S. Smaller Companies, a mutual fund underlying variable insurance products, and the U.S. fund of an investment company whose shares are offered only to non-U.S. investors. Mr. Mohn also is a vice president of Wanger Advisors Trust and the director of domestic research for CWAM.

The SAI provides additional information about the portfolio manager's compensation, other accounts managed and ownership of securities in the Fund.

LEGAL PROCEEDINGS

The Trust, CWAM and the trustees of the Trust (collectively, the "Columbia defendants") are named as defendants in class and derivative complaints, which were consolidated in a Multi-District Action in the federal district court for the District of Maryland on February 20, 2004 (the "MDL Action"). These lawsuits contend that defendants permitted certain investors to market time their trades in certain Columbia Acorn Funds. The MDL Action is ongoing. All claims against the Trust and its independent trustees have been dismissed; however, the interested trustees of the Trust are still parties to the MDL Action.

On March 21, 2005, a class action complaint was filed against the Trust in the Superior Court of the Commonwealth of Massachusetts seeking to rescind the contingent deferred sales charges assessed upon redemption of Class B shares of Columbia Acorn Funds due to the alleged market timing of the Columbia Acorn Funds. In addition to the rescission of sales charges, plaintiffs seek recovery of actual damages, attorneys' fees and costs. The case has been transferred to the MDL Action in the federal district court of Maryland.

The Trust and CWAM are also defendants in a class action lawsuit, filed on November 13, 2003 in the Circuit Court of the Third Judicial Circuit, Madison County, Illinois, that alleges, in summary, that the Trust and CWAM exposed shareholders of Columbia Acorn International to trading by market timers by allegedly (a) failing to properly evaluate daily whether a significant event affecting the value of that fund's securities had occurred after foreign markets had closed but before the calculation of the fund's net asset value; (b) failing to implement the fund's portfolio valuation and share pricing policies and procedures; and (c) failing to know and implement applicable rules and regulations concerning the calculation of net asset value ("Fair Valuation Lawsuit"). On April 5, 2005, the United States Court of Appeals for the Seventh Circuit ruled that the plaintiffs' state law claims were preempted under federal law resulting in the dismissal of plaintiffs' complaint. Plaintiffs appealed the Seventh Circuit's ruling to the United States Supreme Court. On June 15, 2006, the Supreme Court reversed the Seventh Circuit's ruling on jurisdictional grounds, and the case ultimately was remanded to the state court.

18

Managing the Fund

On April 4, 2006, the plaintiffs and the Columbia defendants named in the MDL Action executed an agreement in principle intended to fully resolve all of the lawsuits consolidated in the MDL Action as well as the Fair Valuation Lawsuit. The court entered a stay after the parties executed the agreement in principle. The settlement is subject to court approval.

In 2004, CWAM and the trustees of the Columbia Acorn Trust were named as defendants in certain purported shareholder class and derivative actions making claims, including claims under the Investment Company and the Investment Advisers Acts of 1940 and state law. Certain Columbia Acorn Funds were named as nominal defendants. The suits allege, inter alia, that the fees and expenses paid by the funds are excessive and that the funds' advisers and their affiliates inappropriately used fund assets to distribute the funds and for other improper purposes. On March 2, 2005, the actions were consolidated in the Massachusetts federal court as In re Columbia Entities Litigation. The plaintiffs filed a consolidated amended complaint on June 9, 2005. On November 30, 2005, the judge dismissed all claims by plaintiffs and entered final judgment in favor of the defendants. The plaintiffs appealed to the United States Court of Appeals for the First Circuit on December 30, 2005. A stipulation and settlement agreement dated January 19, 2007 was filed in the First Circuit on February 14, 2007, with a joint stipulation of dismissal and motion for remand to obtain district court approval of the settlement. The joint motion was granted and the appeal was dismissed. On March 6, 2007, the case was remanded to the District Court, where the parties will seek court approval of the settlement. The terms of the proposed settlement, if approved, will require payments by the funds' adviser and/or its affiliates, including payment of plaintiffs' attorneys' fees and notice to class members. In the event that the settlement is not approved, the plaintiffs may elect to g o forward with their appeal and no opinion is expressed regarding the likely outcome or financial impact of such an appeal on any fund.

On or about January 11, 2005, a putative class action lawsuit was filed in federal district court in Massachusetts against the Trust and its trustees, along with Columbia Management Advisors, LLC, the sub-administrator of the Wanger Advisors Funds and the Columbia Acorn Funds. The plaintiffs allege that the defendants failed to submit Proof of Claims in connection with settlements of securities class action lawsuits filed against companies in which the Columbia Acorn Funds held positions. The complaint seeks compensatory and punitive damages, and the disgorgement of all fees paid to Columbia Management Advisors, LLC. Plaintiffs have voluntarily dismissed the Trust and its independent trustees.

The Trust and CWAM intend to defend these suits vigorously.

As a result of these matters or any adverse publicity or other developments resulting from them, there may be increased redemptions or reduced sales of Fund shares, which could increase transaction costs or operating expenses, or have other adverse consequences for the Fund.

However, based on currently available information, the Trust believes that the likelihood that these lawsuits will have a material adverse impact on any fund is remote, and CWAM believes that the lawsuits are not likely to materially affect its ability to provide investment management services to the Fund.

The Fund's principal investment strategies and associated risks are described under "The Fund — Principal Investment Strategies" and "The Fund — Principal Investment Risks." This section describes other investments the Fund may make and the risks associated with them. In seeking to achieve its investment goal, the Fund may invest in various types of securities and engage in various investment techniques, which are not the principal focus of the Fund and therefore are not described in this prospectus. These types of securities and investment practices and their associated risks are identified and discussed in the Fund's SAI, which you may obtain free of

19

Other Investment Strategies and Risks

charge (see back cover). The adviser may elect not to buy any of these securities or use any of these techniques. The Fund may not always achieve its investment goal. Except as otherwise noted, approval by the Fund's shareholders is not required to modify or change the Fund's investment strategies.

THE INFORMATION EDGE

The Fund generally invests in entrepreneurially managed smaller- and mid-sized companies that it believes are not as well known by financial analysts and whose position in a niche creates the opportunity for superior earnings-growth potential. CWAM may identify what it believes are important economic, social or technological trends (for example, the growth of outsourcing as a business strategy, or the productivity gains from the increasing use of technology) and try to identify companies it thinks will benefit from those trends.

In making investments for the Fund, CWAM relies primarily on independent, internally generated research to uncover companies that may be less well known than the more popular names. To find these companies, CWAM compares growth potential, financial strength and fundamental value among companies.

Growth Potential	Financial Strength	Fundamental Value
• superior technology • innovative marketing • managerial skill • market niche • good earnings prospects • strong demand for product	• low debt • adequate working capital • conservative accounting practices • adequate profit margin	• reasonable stock price relative to growth potential and financial strength • valuable assets
The realization of this growth potential would likely produce superior performance that is sustainable over time.	A strong balance sheet gives management greater flexibility to pursue strategic objectives and is important to maintaining a competitive advantage.	Once CWAM uncovers an attractive company, it identifies a price that it believes would also make the stock a good value.

LONG-TERM INVESTING

CWAM's analysts continually screen companies and make contact with more than 1,000 companies around the globe each year. To accomplish this, CWAM analysts often talk directly to top management, vendors, suppliers and competitors.

In managing the Fund, CWAM tries to maintain lower taxes and transaction costs by investing with a long-term time horizon (at least two to five years). However, securities purchased on a long-term basis may be sold within 12 months after purchase due to changes in the circumstances of a particular company or industry, or changes in general market or economic conditions.

DERIVATIVE STRATEGIES

The Fund may enter into a number of derivative strategies, including those that employ futures, options, straddles or similar transactions, to gain or reduce exposure to particular securities or markets. These strategies, commonly referred to as derivatives, involve the use of financial instruments whose values depend on, or are derived from,

20

Other Investments Strategies and Risks

the value of an underlying security, index or currency. The Fund may use these strategies to adjust the Fund's sensitivity to changes in interest rates, or for other hedging purposes (i.e., attempting to offset a potential loss in one position by establishing an interest in an opposite position). Derivative strategies involve the risk that they may exaggerate a loss, potentially losing more money than the actual cost of the underlying security, or limit a potential gain. Also, with some derivative strategies there is a risk that the other party to the transaction may fail to honor its contract terms, causing a loss to the Fund or that the Fund may not be able to find a suitable derivative transaction counterparty, and thus may be unable to invest in derivatives altogether.

TEMPORARY DEFENSIVE STRATEGIES

At times, CWAM may determine that adverse market conditions make it desirable to temporarily suspend the Fund's normal investment activities. During such times, the Fund may, but is not required to, invest in cash or high-quality, short-term debt securities, without limit. Taking a temporary defensive position may prevent the Fund from achieving its investment goal.

21

Financial Highlights

The financial highlights table is intended to help you understand the Fund's Class Z financial performance. Information is shown for the Fund's last five fiscal years, which run from January 1 to December 31. Certain information in the table reflects the financial results for a single Class Z share. The total returns in the table represent the return that you would have earned (or lost) on an investment in the Fund (assuming reinvestment of all dividends and distributions). This information has been derived from the Fund's financial statements, which have been audited for the years ended December 31, 2004, 2005 and 2006 by PricewaterhouseCoopers LLP, an independent registered public accounting firm, whose report, along with the Fund's financial statements, is included in the Fund's annual report. The information for the years ended December 31, 2002 and 2003 is included in the Fund's financial statements that have been audited b y another independent registered public accounting firm, whose report expressed an unqualified opinion on those financial statements and highlights. You can request a free annual report containing those financial statements by calling 1-800-345-6611.

Columbia Acorn USA

	Year ended December 31,
	2006			2005			2004			2003			2002
	Class Z			Class Z			Class Z			Class Z			Class Z
Net asset value — Beginning of period ($)		27.03			25.20			21.01			14.28			17.52
Income from Investment Operations ($)
Net investment income (loss)(a)		(0.02	)		0.07			(0.15	)		(0.13	)		(0.10	)
Net realized and unrealized gain (loss)		2.26			3.18			4.48			6.86			(3.14	)
Total from Investment Operations		2.24			3.25			4.33			6.73			(3.24	)
Less Distributions Declared to Shareholders ($):
From net investment income		—			(0.05	)		—			—			—
From net realized gains		(0.61	)		(1.37	)		(0.14	)		—			—
Total Distributions Declared to Shareholders		(0.61	)		(1.42	)		(0.14	)		—			—
Net Asset Value — End of Period ($)		28.66			27.03			25.20			21.01			14.28
Total Return (%)(b)		8.28	(c)		12.98	(c)		20.62	(c)		47.13			(18.49	)
Ratios to Average Net Assets/Supplemental Data (%):
Expenses(d)		0.98			1.01			1.09			1.11			1.17
Net investment income (loss)(d)		(0.07	)		0.28			(0.66	)		(0.72	)		(0.64	)
Waiver/reimbursement		0.01			0.01			0.02			—			—
Portfolio turnover rate (%)		13			13			18			7			31
Net assets at end of period (in millions) ($)		1,214			937			646			502			235

(a)  Per share data was calculated using average shares outstanding during the period.

(b)  Total return at net asset value assuming all distributions reinvested.

(c)  Had the investment adviser and/or transfer agent not waived and/or reimbursed a portion of expenses, total return would have been reduced.

(d)  The benefits derived from custody fees paid indirectly had no impact.

22

Appendix

Hypothetical Investment and Expense Information

The Fund is required to disclose the following supplemental hypothetical investment information, which provides additional information about the effect of the expenses paid by the Fund, including investment advisory fees and other Fund costs, on the Fund's returns over a 10-year period. The table shows the estimated expenses that would be charged on a hypothetical investment of $10,000 in Class Z shares of the Fund assuming a 5% return each year, the cumulative return after fees and expenses, and the hypothetical year-end balance after fees and expenses. The table also assumes that all dividends and distributions are reinvested. The annual expense ratio used for the Fund, which is the same as that stated in the Annual Fund Operating Expenses table, is presented in the table, and is net of any contractual fee waivers or expense reimbursements for the period of the contractual commitment. Your actual costs may be higher or lower. As noted previously, the Fund's minimum investment for initial purchases or exchanges is $75,000.

Columbia Acorn USA — Class Z Shares

Maximum Sales Charge 0.00%					Initial Hypothetical Investment Amount $10,000.00						Assumed Rate of Return 5%
Year		Cumulative Return Before Fees & Expenses			Annual Expense Ratio			Cumulative Return After Fees & Expenses			Hypothetical Year-End Balance After Fees & Expenses		Annual Fees & Expenses(1)
	1		5.00	%		1.01	%		3.99	%	$	10,399.00	$	103.01
	2		10.25	%		1.01	%		8.14	%	$	10,813.92	$	107.13
	3		15.76	%		1.01	%		12.45	%	$	11,245.40	$	111.40
	4		21.55	%		1.01	%		16.94	%	$	11,694.09	$	115.84
	5		27.63	%		1.01	%		21.61	%	$	12,160.68	$	120.47
	6		34.01	%		1.01	%		26.46	%	$	12,645.89	$	125.27
	7		40.71	%		1.01	%		31.50	%	$	13,150.46	$	130.27
	8		47.75	%		1.01	%		36.75	%	$	13,675.17	$	135.47
	9		55.13	%		1.01	%		42.21	%	$	14,220.81	$	140.87
	10		62.89	%		1.01	%		47.88	%	$	14,788.22	$	146.50
Total Gain After Fees and Expenses											$	4,788.22
Total Annual Fees and Expenses													$	1,236.23

(1)  Annual Fees and Expenses are calculated based on the average between the beginning and ending balance for each year. All information is calculated on an annual compounding basis.

23

Notes

24

Notes

25

Notes

26

FOR MORE INFORMATION

Additional information about the Fund's investments is available in the Fund's semiannual and annual reports to shareholders. The annual report contains a discussion of the market conditions and investment strategies that significantly affected the Fund's performance during its last fiscal year.

You may wish to read the SAI for more information on the Fund and the securities in which it invests. The SAI is incorporated into this prospectus by reference, which means that it is considered to be part of this prospectus.

You can get free copies of annual and semiannual reports and the SAI, request other information and discuss your questions about the Fund by visiting www.columbiafunds.com or by writing or calling the Fund's transfer agent at:

Columbia Management Services, Inc.
P.O. Box 8081
Boston, MA 02266-8081
1-800-345-6611

Text-only versions of all Fund documents can be viewed online or downloaded from the EDGAR database on the Securities and Exchange Commission internet site at www.sec.gov.

You can review and copy information about the Fund, including the SAI, by visiting the following location, and you can obtain copies upon payment of a duplicating fee, by electronic request at the e-mail address publicinfo@sec.gov or by writing the:

Public Reference Room
Securities and Exchange Commission
Washington, DC 20549-0102

Information on the operation of the Public Reference Room may be obtained by calling 1-202-942-8090.

Investment Company Act file number:
Columbia Acorn Trust: 811-01829
•  Columbia Acorn USA

©2007 Columbia Management Distributors, Inc.
One Financial Center, Boston, MA 02111-2621
800.426.3750 www.columbiafunds.com

INT-36/130118-0507

Columbia^SM

Acorn International Select^SM  Prospectus, May 1, 2007

Class A, B and C Shares

Advised by Columbia Wanger Asset Management, L.P.

TABLE OF CONTENTS

THE FUND	2
Investment Goal	2
Principal Investment Strategies	2
Principal Investment Risks	2
Portfolio Holdings Disclosure	4
Performance History	4
Commissions and Other Expenses	6
YOUR ACCOUNT	8
Choosing a Share Class	8
How to Buy Shares	9
Investment Minimums	9
Sales Charges (Commissions)	10
How to Exchange Shares	16
How to Sell Shares	16
Fund Policy on Trading of Fund Shares	17
Other Information About Your Account	20
BOARD OF TRUSTEES	22
MANAGING THE FUND	23
Investment Adviser	23
Portfolio Manager	23
Legal Proceedings	23
OTHER INVESTMENT STRATEGIES AND RISKS	25
The Information Edge	25
Long-Term Investing	25
Derivative Strategies	26
Temporary Defensive Strategies	26
FINANCIAL HIGHLIGHTS	27
APPENDIX	30

Although these securities have been registered with the Securities and Exchange Commission, the Commission has not approved or disapproved any shares offered in this prospectus or determined whether this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Acorn International Select is a trademark owned and registered by Columbia Acorn Trust, Columbia, Columbia Management^® and Columbia Management Services, Inc. are service marks owned and/or registered by Bank of America

The Fund

INVESTMENT GOAL

Columbia Acorn International Select (Acorn International Select^SM) seeks long-term growth of capital.

PRINCIPAL INVESTMENT STRATEGIES

Acorn International Select invests generally in the stocks of companies based in developed markets (for example, Japan, Canada and the United Kingdom) outside the United States. The Fund invests in at least three countries. The Fund is a diversified fund that takes advantage of its adviser's research and stockpicking capabilities to invest in a limited number of foreign companies (between 40-60), offering the potential to provide above-average growth over time. The Fund invests primarily in companies with market capitalizations of $2 billion to $25 billion, at the time of initial purchase. Although the Fund primarily invests in small- and medium-sized companies, at times the Fund may invest in larger-size companies.

Acorn International Select believes that companies within this capitalization range, which are not as well known by financial analysts, may offer higher return potential than the stocks of companies with capitalizations above $25 billion.

Acorn International Select typically looks for companies with:

•  A strong business franchise that offers growth potential.

•  Products and services that give the company a competitive advantage.

•  A stock price the Fund's investment adviser believes is reasonable relative to the assets and earning power of the company.

Acorn International Select is an international fund and, under normal circumstances, invests at least 65% of its net assets in the stocks of foreign companies based in developed markets outside the United States.

Additional strategies that are not principal investment strategies and the risks associated with them are described later in this prospectus under "Other Investment Strategies and Risks."

PRINCIPAL INVESTMENT RISKS

The principal risks of investing in the Fund are described below. There are many circumstances (including additional risks that are not described here) which could prevent the Fund from achieving its investment goal. You may lose money by investing in the Fund.

Management risk means that the adviser's other investment decisions might produce losses or cause the Fund to underperform when compared to other funds with a similar investment goal. Market risk means that security prices in a market, sector or industry may fall, reducing the value of your investment. Because of management and market risk, there is no guarantee that the Fund will achieve its investment goal or perform favorably among comparable funds.

Since the Fund purchases equity securities, it is subject to equity risk. This is the risk that stock prices will fall over short or extended periods of time. Although the stock market historically has outperformed other asset classes over the long term, the stock market tends to move in cycles. Individual stock prices may fluctuate drastically from day-to-day and may underperform other asset classes over an extended period of time.

2

The Fund

Because the Fund invests in stocks, the price of its shares—its net asset values (NAV) per share—fluctuates daily in response to changes in the market value of stocks.

Individual companies may report poor results or be negatively affected by industry and/or economic trends and developments. The prices of securities issued by such companies may suffer a decline in response. These price movements may result from factors affecting individual companies, industries or the securities market as a whole.

Sector risk is inherent in the Fund's investment strategy. Companies that are in different but closely related industries are sometimes described as being in the same broad economic sector. The values of stocks of different companies in a market sector may be similarly affected by particular economic or market events. Although the Fund does not intend to focus on any particular sector, at times, the Fund may have a large portion of its assets invested in a particular sector.

Foreign securities are subject to special risks. Foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the dollar value of foreign securities denominated in foreign currencies and U.S. dollars, without a change in the intrinsic value of those securities. The liquidity of foreign securities may be more limited than that of domestic securities, which means that the Fund may, at times, be unable to sell foreign securities at desirable prices. Brokerage commissions, custodial fees and other fees are generally higher for foreign investments. In addition, foreign governments may impose withholding taxes that would reduce the amount of income and capital gains available to distribute to shareholders. Other risks include possible delays in the settlement of transactions or in the notification of income; less publicly av ailable information about companies; the impact of political, social or diplomatic events; possible seizure, expropriation or nationalization of the company or its assets; and possible imposition of currency exchange controls.

Market timers. Because the Fund invests predominantly in foreign securities, the Fund may be particularly susceptible to market timers. Market timers generally attempt to take advantage of the way the Fund prices its shares by trading based on market information they expect will lead to a change in the Fund's net asset value on the next pricing day. Market timing activity may be disruptive to Fund management and, since a market timer's profits are effectively paid directly out of the Fund's assets, may negatively impact the investment returns of other shareholders. Although the Fund has adopted certain policies and methods intended to identify and discourage frequent trading based on this strategy, it cannot ensure that all such activity can be identified or terminated.

Investments in emerging markets are subject to additional risk. The risks of foreign investments are typically increased in less developed countries, which are sometimes referred to as emerging markets. For example, political and economic structures in these countries may be new and developing rapidly, which may cause instability. These countries are also more likely to experience high levels of inflation, deflation or currency devaluations, which could hurt their economies and securities markets.

Small- or mid-cap companies may be more susceptible to market downturns, and their prices could be more volatile than large-cap companies. These companies are more likely than larger companies to have limited product lines, operating histories, markets or financial resources. They may depend heavily on a small management team and may trade less frequently, may trade in smaller volumes and may fluctuate more sharply in price than stocks of larger companies. In addition, such companies may not be widely followed by the investment community, which can lower the demand for their stocks.

An investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

3

The Fund

PORTFOLIO HOLDINGS DISCLOSURE

A description of the Fund's policies and procedures with respect to the disclosure of its portfolio securities is available in the Fund's Statement of Additional Information (SAI), which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611.

The Fund posts its complete portfolio holdings at as of month-end www.columbiafunds.com approximately 30-40 calendar days after such month-end. Additionally, the Fund discloses its top 15 month-end portfolio holdings at www.columbiafunds.com, on or about 15 calendar days following such month-end.

Once posted, the above information will remain available on the website until at least the date on which the Fund files a Form N-CSR or Form N-Q for the period that includes the date as of which the information is current.

PERFORMANCE HISTORY

The bar chart below shows the Fund's calendar-year total returns (before taxes) for its Class A shares, excluding sales charges. The performance table following the bar chart shows how the Fund's average annual total returns for Class A, B and C shares, including sales charges, compare with a broad measure of market performance for one year, five years and the life of the share class. The chart and table are intended to illustrate some of the risks of investing in the Fund by showing the changes in the Fund's performance from year to year. All returns include the reinvestment of dividends and distributions. As with all mutual funds, past performance (before and after taxes) does not predict the Fund's future performance.

UNDERSTANDING PERFORMANCE

Calendar Year Total Returns show the Fund's Class A share performance for each completed calendar year since the Class commenced operations. Those returns include the effects of Fund expenses, but not the effects of sales charges paid directly by the shareholder. If sales charges were included, these returns would be lower.

Average Annual Total Returns are a measure of the Fund's average performance over the past one year, five years and the life of the share class. The table shows returns of each share class and includes the effects of both fund expenses and current sales charges. Class B share returns do not reflect Class A share returns after conversion of Class B shares to Class A shares — see the section "Your Account — Sales Charges (Commissions)."

The Fund's returns are compared to the S&P/Citigroup World ex-U.S. Cap Range $2-10 Billion Index (S&P/Citigroup Cap Range 2-10B). The S&P/Citigroup Cap Range $2-10B is Citigroup's two to ten billion U.S. dollar security market subset of its Broad Market Index. It represents a midcap developed market index, excluding the U.S. Unlike the Fund, an index is not an investment, does not incur fees, expenses or taxes, and is not professionally managed.

4

The Fund

Calendar Year Total Returns (Class A)

For the periods shown in bar chart:
Best quarter: 2nd quarter 2003, +19.55%
Worst quarter: 3rd quarter 2001, -22.88%

After-tax returns are calculated using the highest historical individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on each investor's own tax situation and may differ from those shown. After-tax returns may not be relevant to investors who hold Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Average Annual Total Returns — for periods ended December 31, 2006⁽¹⁾

Share Class	1 Year		5 Years		Life of the Share Class(2)
Class A (%)
Return Before Taxes		28.15		17.03		6.80
Return After Taxes on Distributions		28.15		17.06		6.80
Return After Taxes on Distributions and Sale of Fund Shares		18.30		15.12		5.95
Class B (%)
Return Before Taxes		30.00		17.43		7.09
Return After Taxes on Distributions		30.00		17.49		7.12
Return After Taxes on Distributions and Sale of Fund Shares		19.50		15.50		6.22
Class C (%)
Return Before Taxes		33.85		17.58		7.06
Return After Taxes on Distributions		33.85		17.64		7.09
Return After Taxes on Distributions and Sale of Fund Shares		22.00		15.64		6.20
Index
S&P/Citigroup Cap Range $2-10B (%)		27.88		21.24		14.23	(3)

(1)  Performance may reflect any voluntary waiver or reimbursement of Fund expenses by the investment adviser or its affiliates. Absent these waivers or reimbursement arrangements, performance results would have been lower.

(2)  The inception date for Class A, Class B and Class C shares is October 16, 2000.

(3)  Performance information is from October 16, 2000.

5

The Fund

COMMISSIONS AND OTHER EXPENSES

Expenses are one of several factors to consider before you invest in a mutual fund. The tables below describe the commissions and other expenses you may pay when you buy, hold and sell shares of the Fund.

UNDERSTANDING EXPENSES

Sales Charges (Commissions) are paid directly by shareholders to Columbia Management Distributors, Inc., the Fund's distributor, who compensates your financial advisor.

Annual Fund Operating Expenses are paid by the Fund. They include management and administration fees, 12b-1 fees and other expenses that generally include, but are not limited to, transfer agency, custody, and legal fees as well as costs related to state registration and printing of Fund documents. The specific fees and expenses that make up the Fund's other expenses will vary from time to time and may include fees or expenses not described here. The Fund will likely incur portfolio transaction costs that are in addition to the total annual fund operating expenses disclosed in the fee table. These transaction costs are made up of all costs that are associated with trading securities for the Fund's portfolio and include, but are not limited to, brokerage commissions and market spreads, as well as potential changes to the price of a security due to the Fund's efforts to purchase or sell it. While certain elements of transaction costs are readily identifiable and quantifiable, other elements that can make up a significant amount of the Fund's transaction costs are not. Higher transaction costs reduce the Fund's returns.

Shareholder Fees (commissions paid directly from your investment)

	Class A			Class B		Class C
Maximum sales charge (load) on purchases (%) (as a percentage of the offering price)		5.75		None		None
Maximum deferred sales charge (load) on redemptions (%) (as a percentage of the lesser of purchase price or redemption price)		1.00	(1)		5.00		1.00
Redemption fee (%) (as a percentage of amount redeemed, if applicable)	None(2)(3)			None(2)(3)		None(2)(3)

(1)  This charge applies only to certain purchases of Class A shares bought without an initial sales charge that are sold within 12 months of purchase.

(2)  There is a $7.50 charge for wiring sale proceeds to your bank.

(3)  A redemption fee of 2.00% may be charged on shares that were owned for 60 days or less. For more information, see "Fund Policy on Trading of Fund Shares" below.

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The Fund

Annual Fund Operating Expenses (deducted directly from Fund assets)

	Class A		Class B		Class C
Management fees(1) (%)		0.94		0.94		0.94
Distribution and service (12b-1) fees(2) (%)		0.25		0.75		1.00
Other expenses(3) (%)		0.44		0.54		0.48
Total annual fund operating expenses(4) (%)		1.63		2.23		2.42

(1)  The Fund pays an investment advisory fee of 0.94%. In addition to the management fee, the Fund and the other funds of Columbia Acorn Trust (the "Trust") pay the adviser an administrative fee based on the average daily aggregate net assets of the Trust at the following annual rates: 0.05% of net assets up to $8 billion; 0.04% of the next $8 billion; and 0.03% of net assets in excess of $16 billion. Based on the Trust's average daily net assets as of December 31, 2006, the administrative fee would be at a rate of 0.04% and is included in "Other expenses."

(2)  The distribution and service (12b-1) fees for Class B shares have been restated to reflect a reduction of the distribution fee rate by 0.10%, effective August 1, 2006.

(3)  "Other expenses" have been restated to reflect contractual changes to the transfer agency fees paid by the Fund.

(4)  The Fund's adviser has voluntarily agreed to reimburse the Fund for any ordinary operating expenses (exclusive of distribution and service fees, interest, taxes and extraordinary expenses, if any) exceeding the annual rate of 1.45% of the average daily net assets for Class A, Class B and Class C shares. This arrangement may be modified or terminated by either the Fund or its adviser on 30 days notice. As a result, the actual total annual fund operating expenses for Class B would be 2.20%.

Example Expenses help you compare the cost of investing in the Fund to the cost of investing in other mutual funds. The table does not take into account any expense reduction arrangements discussed in the footnotes to the Annual Fund Operating Expenses table. It uses the following hypothetical conditions:

•  $10,000 initial investment

•  5% total return for each year

•  Fund operating expenses remain the same

•  Reinvestment of all dividends and distributions

•  Class B shares convert to Class A shares after eight years

Example Expenses for a $10,000 investment (your actual costs may be higher or lower)

Class		1 Year		3 Years		5 Years		10 Years
Class A:		$	731	$	1,060	$	1,411	$	2,397
Class B:	did not sell your shares	$	226	$	697	$	1,195	$	2,414
	sold all your shares at the end of the period	$	726	$	997	$	1,395	$	2,414
Class C:	did not sell your shares	$	245	$	755	$	1,291	$	2,756
	sold all your shares at the end of the period	$	345	$	755	$	1,291	$	2,756

See the Appendix for additional hypothetical investment and expense information.

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Your Account

CHOOSING A SHARE CLASS

The Fund offers three classes of shares in this prospectus — Class A, Class B and Class C. Each share class has its own commission and expense structure that affects the investment return of that class. Determining which share class is best for you depends on various factors, including the amount you are investing, how long you expect to hold your investment and your personal situation.

You should consult with your financial advisor before deciding which share class is most appropriate for you. The following considerations should be part of your assessment:

•  You will pay a commission if you buy Class A, B or C shares, either at the time of investment or redemption, or through ongoing distribution commission payments (Rule 12b-1 fees) made from your investment over time, or both.

•  Class A shares require an up-front commission payment, but pay lower ongoing Rule 12b-1 fees than Class B and Class C shares. Class B and Class C shares have no up-front commission paid by the shareholder but pay higher ongoing commissions (Rule 12b-1 fees), a deferred commission is imposed on a redemption of Class B shares within six years after purchase, and a deferred commission is imposed on a redemption of Class C shares with one year of purchase. The differential between classes will vary depending on the actual investment return for any given period.

•  Class A shares can be more advantageous to an investor who intends to hold the shares for several years and invests an amount large enough to qualify for a reduced rate of initial sales commission, taking into account the commissions that investor may pay when redeeming shares of other classes. To project whether Class A shares might be more advantageous to you, you should consider, among other factors, the time period you intend to hold the shares, your initial sales commission and a comparison of the total annual expenses of Class A shares to the expenses of other share classes. Class A shares pay an ongoing annual commission (Rule 12b-1 fee) of up to 0.25% of the average value of the shares.

•  Class B shares pay an ongoing annual commission (Rule 12b-1 fee) of up to 0.75% of the average value of the shares and automatically convert to Class A shares after eight years. A Class B shareholder of the Fund whose account has a value of less than $50,000 (including for this purpose the combined value of all eligible accounts maintained by that shareholder that would be used to determine eligibility for reduced sales charges on Class A shares) may purchase additional Class B shares of the Fund to increase the account value up to a maximum of $49,999; any additional investment by the shareholder in that Fund will be invested in Class A shares of the Fund, without regard to the normal investment minimum for Class A shares, but will be subject to the applicable Class A shares up-front commission.

•  Class C shares are generally more advantageous to an investor who intends to hold shares for only a few years. Class C shares pay an ongoing annual commission (Rule 12b-1 fee) of up to 1.00% of the average value of the shares.

•  If you invest $1 million or more, you can purchase Class A shares but not Class C shares.

The Fund also offers an additional class of shares, Class Z shares, exclusively to certain institutional and other eligible investors. Class Z shares are made available through a separate prospectus provided to eligible institutional and other investors.

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Your Account

HOW TO BUY SHARES

Your financial advisor can help you establish an appropriate investment portfolio, buy shares and monitor your investments. When the Fund receives your purchase request in "good form," your shares will be bought at the next calculated public offering price. "Good form" means that the Fund's transfer agent has all information and documentation it deems necessary to effect your order. For example "good form" may mean that you have properly placed your order with your financial advisor or the Fund's transfer agent has received your completed application, including all necessary signatures. The Fund reserves the right to refuse a purchase order for any reason, including if the Fund believes that doing so would be in the best interest of the Fund and its shareholders. The USA PATRIOT Act may require us to obtain certain personal information from you that we will use to verify your identity. If you do not provide the information, we m ay not be able to open your account. If we are unable to verify your customer information, we reserve the right to close your account or take such other steps as we deem reasonable.

INVESTMENT MINIMUMS

The minimum initial investment for Class A, Class B and Class C shares generally is $2,500. The investment minimum is applied at the class level. For individual retirement plans (including traditional IRAs, Roth IRAs and Coverdell Education Savings Accounts) and non-omnibus group retirement accounts, the minimum initial investment is $1,000. For non-omnibus group retirement plans, the investment minimum is determined based on the plan's investment rather than on the separate investments of its individual participants. For investors establishing an automatic investment plan, the minimum initial investment is $50. There is no minimum initial investment for omnibus accounts or wrap accounts.

The minimum investment for additional purchases of Class A, Class B and Class C shares is $50 for all investors.

The Fund reserves the right to change these investment minimums. The Fund also reserves the right to refuse a purchase order for any reason, including if it believes that doing so would be in the best interest of the Fund and its shareholders. In addition, pursuant to the Trust's Agreement and Declaration of Trust, the Fund reserves the right to redeem your shares if your account falls below the minimum investment restrictions.

Please see the SAI for more details on investment minimums.

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Your Account

Outlined below are the various options for buying shares:

Method	Instructions
Through your financial advisor	Your financial advisor can help you establish your account and buy Fund shares on your behalf. To receive the current trading day's price, your financial advisor must receive your request prior to the close of regular trading on the New York Stock Exchange (NYSE), usually 4:00 p.m. Eastern time. Your financial advisor may charge you fees for executing the purchase for you.
By check (new account)	For new accounts, send a completed application and check made payable to the Fund to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By check (existing account)	For existing accounts, fill out and return the additional investment stub included in your account statement, or send a letter of instruction including your Fund name and account number with a check made payable to the Fund and mailed to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By exchange	You or your financial advisor may acquire Fund shares for your account by exchanging shares you own in a different fund distributed by Columbia Management Distributors, Inc. for shares of the same class (and, in some cases, certain other classes) of the Fund at no additional cost. An exchange to another fund may incur a sales charge if the original purchase was not assessed a sales charge. To exchange by telephone, call 1-800-422-3737. Please see "How to Exchange Shares" for more information.
By wire	You may purchase Fund shares by wiring money from your bank account to your Fund account. To wire funds to your Fund account, call 1-800-422-3737 for wiring instructions.
By electronic funds transfer	You may purchase Fund shares by electronically transferring money from your bank account to your Fund account by calling 1-800-422-3737. An electronic funds transfer may take up to two business days to settle and must be considered in "good form." You must set up this feature prior to your telephone request. Be sure to complete the appropriate section of the application for this feature.
Automatic investment plan	You may make monthly or quarterly investments ($50 minimum) automatically from your bank account to your Fund account. You may select a pre-authorized amount to be sent via electronic funds transfer. Be sure to complete the appropriate section of the application for this feature.
Automated dollar cost averaging	You may purchase Fund shares for your account by exchanging $100 or more each month from another fund for shares of the same class of the Fund at no additional cost. Exchanges will continue so long as your fund balance is sufficient to complete the transfers. You may terminate your program or change the amount of the exchange (subject to the $100 minimum) by calling 1-800-345-6611. There may be an additional sales charge if exchanging from a money market fund. Be sure to complete the appropriate section of the account application for this feature.
By dividend diversification	You may automatically invest dividends distributed by another fund into the same class of shares (and, in some cases, certain other classes) of the Fund at no additional sales charge. There may be an additional sales charge if automatically investing dividends from a money market fund. To invest your dividends in the Fund, call 1-800-345-6611.
Through the internet	You may purchase Fund shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet purchases. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

SALES CHARGES (COMMISSIONS)

You may be subject to an initial sales charge when you purchase, or a contingent deferred sales charge (CDSC) when you sell, shares of the Fund. These sales charges are described below. In certain circumstances, the sales charge may be reduced or waived, as described below and in the SAI.

Rule 12b-1 Plan The Fund has adopted a plan under Rule 12b-1 under the Investment Company Act that permits it to pay its distributor ongoing sales and marketing fees (commissions) to support the sale and distribution of Class A, B and C shares and certain services provided to you by your financial advisor, and your financial advisor may receive all or a portion of those fees attributable to your shares. The annual fee, as a percentage of the value of the shares, is normally 0.25% for Class A, 0.75% for Class B and 1.00% for Class C shares. These fees are

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paid out of the assets of these share classes. Over time, these fees reduce the return on your investment. Class B shares automatically convert to Class A shares after eight years, eliminating a portion of the Rule 12b-1 fee thereafter.

Financial Intermediary Payments

The Fund's distributor, investment adviser or their affiliates may make payments, from their own resources, to certain financial intermediaries, including other Bank of America affiliates, for marketing support services. For purposes of this section the term "financial intermediary" includes any broker, dealer, bank, bank trust department, registered investment adviser, financial planner, retirement plan or other third-party administrator and any other institution having a selling, services or any similar agreement with the Fund's distributor, investment adviser or one of their affiliates. These payments are generally based upon one or more of the following factors: average net assets of the mutual funds distributed by the Fund's distributor attributable to that financial intermediary, gross sales of the mutual funds distributed by the Fund's distributor attributable to that financial intermediary, reimbursement of ticket charge s (fees that a financial intermediary firm charges its representatives for effecting transactions in fund shares) or a negotiated lump sum payment.

While the financial arrangements may vary for each financial intermediary, the payments to any one financial intermediary are generally expected to be between 0.05% and 0.35% on an annual basis for payments based on average net assets of the Fund attributable to the financial intermediary, and between 0.10% and 0.25% on an annual basis for firms receiving a payment based on gross sales of the Fund attributable to the financial intermediary. The Fund's distributor, investment adviser or their affiliates may make payments in materially larger amounts or on a basis materially different from those described above when dealing with other affiliates of Bank of America. Such increased payments to the other Bank of America affiliate may enable the other Bank of America affiliate to offset credits that it may provide to its customers in order to avoid having such customers pay fees to multiple Bank of America entities in connection with the customer's investment in the Fund.

Payments also may be made to certain financial intermediaries, including other Bank of America affiliates, that provide investor services to retirement plans and other investment programs to compensate financial intermediaries for services they provide to such programs, including, but not limited to, sub-accounting, sub-transfer agency, similar shareholder or participant recordkeeping, shareholder or participant reporting, or shareholder or participant transaction processing. These payments for investor servicing support vary by financial intermediary but generally are not expected, with certain limited exceptions, to exceed 0.35% of the total Fund assets for Class A, B and C shares in the program on an annual basis.

The Trust's Board of Trustees has authorized the Fund to pay to any intermediary up to 0.05% of the average aggregate value of Fund shares in the intermediary's program on an annual basis for providing investor services. Charges of an intermediary in excess of that paid by the Fund will be borne by the Fund's distributor or its affiliaites.

The Fund's distributor, investment adviser or their affiliates may make other payments or allow promotional incentives to financial intermediaries to the extent permitted by the rules of the Securities and Exchange Commission, the National Association of Securities Dealers and by other applicable laws and regulations.

Amounts paid by the Fund's distributor, investment adviser or their affiliates are paid out of the distributor's, investment adviser's or their affiliates' own resources and do not increase the amount paid by you or the Fund. You can find further details about the payments made by the Fund's distributor, investment adviser or their

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Your Account

affiliates and the services provided by financial intermediaries as well as a list of the financial intermediaries to which the Fund's distributor, investment adviser or their affiliates have agreed to make marketing support payments in the Fund's SAI, which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611. Your financial intermediary may charge you fees or commissions in addition to those disclosed in this prospectus. You can ask your financial intermediary for information about any payments it receives from the Fund's distributor, investment adviser and their affiliates and any services your financial intermediary provides, as well as fees and/or commissions it charges. In addition, depending on the financial arrangement in place at any particular time, a fi nancial intermediary and its financial consultants also may have a financial incentive for recommending a particular fund or share class over others. You should consult with your financial adviser and review carefully any disclosure by the financial intermediary as to compensation received by your financial adviser.

Class A shares Your purchases of Class A shares are made at the public offering price for these shares. This price includes a sales charge that is based on the amount of your initial investment when you open your account. The sales charge you pay on an additional investment is based on the total amount of your purchase and the current value of your account. Shares you purchase with reinvested dividends or other distributions are not subject to a sales charge. A portion of the sales charge is paid as a commission to your financial advisor on your sale of Class A shares. The amount of the sales charge differs depending on the amount you invest as shown in the table below.

Class A Sales Charges

	Sales Charge as % of:				% of offering price
Amount of purchase	offering price		net amount invested		retained by financial advisor
Less than $50,000		5.75		6.10		5.00
$50,000 to less than $100,000		4.50		4.71		3.75
$100,000 to less than $250,000		3.50		3.63		2.75
$250,000 to less than $500,000		2.50		2.56		2.00
$500,000 to less than $1,000,000		2.00		2.04		1.75
$1,000,000 or more		0.00		0.00		0.00

In addition to the initial sales charge paid to your financial advisor and distributor, a 0.25% annual commission is paid to your financial advisor over the life of your investment out of your Fund assets as a 12b-1 fee.

The Fund's distributor may also pay additional compensation to financial advisors as an incentive for promoting the sale of shares of funds that it distributes.

Class A shares bought without an initial sales charge in accounts aggregating $1 million to $50 million at the time of purchase are subject to a 1.00% CDSC if the shares are sold within 12 months of the time of purchase. Subsequent Class A share purchases that bring your account value above $1 million (but less than $50 million) are subject to a CDSC if redeemed within 12 months of the date of purchase. The 12-month period begins on the first day of the month in which the purchase was made. The CDSC does not apply to retirement plans purchasing shares through a fee-based program.

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Your Account

For Class A share purchases of $1 million or more, financial advisors receive a cumulative commission from the distributor as follows:

Purchases Over $1 Million

Amount purchased	Commission %
$1 million to less than $3 million		1.00
$3 million to less than $50 million		0.50
$50 million or more		0.25

For group retirement plans, financial advisors are eligible to receive a 1.00% commission from the distributor on purchases, including those in amounts less than $1 million, that are coded as commission eligible trades. In determining the commission payable to a financial advisor in the above table, the breakpoint discount policies described in "Reduced Sales Charges (Commissions) for Larger Investments," below, shall apply.

UNDERSTANDING CONTINGENT DEFERRED SALES CHARGES (COMMISSIONS)

Certain investments in Class A, B and C shares are subject to a CDSC, a sales charge applied at the time you sell your shares. You will pay the CDSC only on shares you sell within a certain amount of time after purchase. The CDSC generally declines each year until there is no charge for selling shares. The CDSC is applied to the net asset value at the time of purchase or sale, whichever is lower. For purposes of calculating the CDSC, the start of the holding period is the first day of the month in which the purchase was made. Shares you purchase with reinvested dividends or other distributions are not subject to a CDSC. When you place an order to sell shares, the Fund will automatically sell first those shares not subject to a CDSC and then those you have held the longest.

Reduced Sales Charges (Commissions) for Larger Investments.

A.  What are the principal ways to obtain a breakpoint discount?

There are two principal ways you may pay a lower sales charge (often referred to as "breakpoint discounts") when purchasing Class A shares of the Fund and other funds in the Columbia family of funds.

Rights of Accumulation The value of eligible accounts maintained by you and each member of your immediate family may be combined with the value of your current purchase to reach a sales charge discount level (according to the chart on the previous page) and to obtain the lower sales charge for your current purchase. To calculate the combined value of the accounts, the Fund will use the shares' current public offering price.

Statement of Intent You also may pay a lower sales charge when purchasing Class A shares by signing a Statement of Intent. By doing so, you would be able to pay the lower sales charge on all purchases made under the Statement of Intent within 13 months. As described in the chart on the previous page, the first breakpoint discount will be applied when total purchases reach $50,000. If your Statement of Intent purchases are not completed within 13 months, you will be charged the applicable sales charge on the amount you had invested to that date. To calculate the total value of your Statement of Intent purchases, the Fund will use the historic cost (i.e. dollars invested) of the shares held in each eligible account. You must retain all records necessary to substantiate historic costs because the Fund and your financial intermediary may not maintain this information.

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Your Account

B.  What accounts are eligible for breakpoint discounts?

The types of eligible accounts that may be aggregated to obtain one or both of the breakpoint discounts described above include:

•  Individual accounts

•  Joint accounts

•  Certain IRA accounts

•  Certain trusts

•  UTMA/UGMA accounts

For the purposes of obtaining a breakpoint discount, members of your "immediate family" include your spouse, parent, stepparent, legal guardian, child, stepchild, father-in-law and mother-in-law. Eligible accounts include those registered in the name of your dealer or other financial intermediary through which you own Columbia fund shares. An account is not eligible to the extent it holds an institutional class of shares of a Columbia money market fund or Class R shares of any Columbia fund. The value of your investment in a non-institutional class of a Columbia money market fund held in an eligible account may be aggregated with your investments in other funds in the Columbia family of funds to obtain a breakpoint discount through a Right of Accumulation. Non-institutional class investments in Columbia money market funds may also be included in the aggregation for a Statement of Intent for shares that have been charged a commis sion.

C.  How do I obtain a breakpoint discount?

The steps necessary to obtain a breakpoint discount depend on how your account is maintained with the Columbia family of funds. To obtain any of the above breakpoint discounts, you must notify your financial advisor at the time you purchase shares of the existence of each eligible account maintained by you or your immediate family. It is the sole responsibility of your financial advisor to ensure that you receive discounts for which you are eligible, and the Fund is not responsible for a financial advisor's failure to apply the eligible discount to your account. You may be asked by the Fund or your financial advisor for account statements or other records to verify your discount eligibility, including, where applicable, records for accounts opened with a different financial advisor and records of accounts established by members of your immediate family. If you own shares exclusively through an account maintained with the Fund's transfer agent, Columbia Management Services, Inc., you will need to provide the foregoing information to a Columbia Management Services, Inc. representative at the time you purchase shares.

D.  How can I obtain more information about breakpoint discounts?

Certain investors, including affiliates of the Fund, broker/dealers and their affiliates, investors in wrap-fee programs through fee-based advisers or certain retirement plans, certain shareholders of funds that were reorganized into other Columbia funds, and investors using the proceeds of redemptions of Fund shares or of certain Bank of America trust or similar accounts may purchase shares at a reduced sales charge or net asset value, which is the value of a fund share excluding any sales charges. CDSCs may also be waived for redemptions under a systematic withdrawal program, in connection with the death or post-purchase disability of a shareholder, certain medical expenses, charitable gifts, involuntary and tax-related redemptions, or when the selling broker/dealer has agreed to waive or return its commission. Restrictions may apply to certain accounts and certain transactions. Further information regarding these discounts ma y be found in the Fund's SAI, which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611.

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Class B shares Your purchases of Class B shares are at Class B's net asset value. Purchases in Class B shares may not result in the account holding $50,000 or more of Class B shares (including for this purpose the combined value of all eligible accounts maintained by you that would be used to determine eligibility for reduced sales charges on Class A shares). In the event that an existing Class B shareholder seeks to add funds to such an account so that the balance would be in excess of $49,999, the amount in excess may be invested in Class A shares without the imposition of the minimum investment requirement for Class A shares. Such purchases of Class A shares will be subject to the applicable sales load imposed on such purchases. See "Class A Sales Charges" on page 12.

Class B shares have no front-end sales charge, but they do carry a CDSC that is imposed only on shares sold within six years of purchase. The CDSC declines over the six years and disappears in the seventh year. The distributor pays your financial advisor an up-front commission on sales of Class B shares as described in the chart below. In addition, Class B shares bear ongoing service and distribution fees that are higher than those borne by Class A shares.

Purchases of less than $50,000:

Class B Sales Charges

Holding period after purchase	% deducted when shares are sold1
Through first year		5.00
Through second year		4.00
Through third year		3.00
Through fourth year		3.00
Through fifth year		2.00
Through sixth year		1.00
Longer than six years		0.00

(1)  Applied to the net asset value at the time of purchase or sale, whichever is lower.

In addition, from the annual fee of 0.75% of the value of your shares paid out of your Fund assets as Rule 12b-1 fees, the distributor receives 0.50% of the value of the shares for each of the first eight years, or an aggregate 4.00% over eight years, which will offset the commission it paid to your financial advisor. Your financial advisor is paid the remaining 0.25% as an ongoing commission for the life of your investment.

The conversion of Class B shares to Class A shares occurs automatically eight years after purchase.

Class C shares Your purchases of Class C shares are at Class C's net asset value. Although Class C shares have no front-end sales charge, they carry a CDSC of 1.00% that is applied to shares sold within the first year after they are purchased. After holding shares for one year, you may sell them at any time without paying a CDSC. The distributor pays your financial advisor an up-front commission of 1.00% on your purchases of Class C shares, for which the distributor is repaid from the ongoing annual fee of 1.00% of the value of your shares paid out of your Fund assets as Rule 12b-1 fees, which is higher than the Rule 12b-1 fees borne by Class A and Class B shares.

Class C Sales Charges

Holding period after purchase	% deducted when shares are sold1
Through one year		1.00
Longer than one year		0.00

(1)  Applied to the net asset value at the time of purchase or sale, whichever is lower.

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A 1.00% annual commission is paid to your financial advisor and the distributor over the life of your investment out of your Fund assets.

HOW TO EXCHANGE SHARES

You may exchange your shares for shares of the same share class (and in some cases, certain other classes) of another fund distributed by Columbia Management Distributors, Inc. at net asset value. If your shares are subject to a CDSC, you will not be charged a CDSC upon the exchange. However, when you sell the shares acquired through the exchange, the shares sold may be subject to a CDSC, depending upon when you originally purchased the shares you are exchanging. For purposes of computing the CDSC, the length of time you have owned your shares will be computed from the date of your original purchase and the applicable CDSC will be the CDSC of the original fund. Shareholders of Columbia Acorn Funds that qualify to purchase Class A shares at net asset value may exchange their Class A shares for Class Z shares of another fund distributed by Columbia Management Distributors, Inc. (see the SAI for a description of these situations.) Unless your account is part of a tax-deferred retirement plan, an exchange is a taxable event, and you may realize a gain or a loss for tax purposes. The Fund may terminate your exchange privilege if the adviser determines that your exchange activity is likely to adversely impact its ability to manage the Fund. See "Fund Policy on Trading of Fund Shares" for the Fund's policy. To exchange by telephone, call 1-800-422-3737. Please have your account and taxpayer identification numbers available when calling.

You also may exchange your shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet exchanges. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

HOW TO SELL SHARES

Your financial advisor can help you determine if and when you should sell your shares. You may sell shares of the Fund on any regular business day that the NYSE is open.

When the Fund receives your sales request in "good form," shares will be sold at the next calculated net asset value. "Good form" means that the Fund's transfer agent has all information and documentation it deems necessary to effect your order. For example, when selling shares by letter of instruction, "good form" means (i) your letter has complete instructions, the proper signatures and Medallion Signature Guarantees, (ii) if applicable, you have included any certificates for shares to be sold, and (iii) any other required documents are attached. For additional documents required for sales by corporations, agents, fiduciaries, surviving joint owners and other legal entities, please call 1-800-345-6611. Retirement plan accounts have special requirements; please call 1-800-799-7526 for more information.

The Fund will generally send proceeds from the sale to you within seven days (usually on the next business day after your request is received in "good form"). However, if you purchased your shares by check, the Fund may delay sending the proceeds from the sale of your shares for up to 10 days after your purchase to protect against checks that are returned. No interest will be paid on uncashed redemption checks. Redemption proceeds may be paid in securities rather than cash, under certain circumstances. For more information, see the paragraph "Non-Cash Redemptions" under the section "How to Sell Shares" in the SAI.

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Your Account

During any 90-day period for any one shareholder, the Fund is obligated to redeem shares solely in cash up to the lesser of $250,000 or 1% of the Fund's net assets. Redemptions in excess of these limits will normally be paid in cash, but may be paid wholly or partly by an in-kind distribution of securities.

Outlined below are the various options for selling shares:

Method	Instructions
Through your financial advisor	You may call your financial advisor to place your sell order. To receive the current trading day's price, your financial advisor must receive your request prior to the close of regular trading on the NYSE, usually 4:00 p.m. Eastern time. Your financial advisor may charge you fees for executing a redemption for you.
By exchange	You or your financial advisor may sell Fund shares by exchanging from the Fund into the same share class (and, in some cases, certain other classes) of another fund distributed by Columbia Management Distributors, Inc. at no additional cost. To exchange by telephone, call 1-800-422-3737.
By telephone	You or your financial advisor may sell Fund shares by telephone and request that a check be sent to your address of record by calling 1-800-422-3737, unless you have notified the Fund of an address change within the previous 30 days. The dollar limit for telephone sales is $100,000 in a 30-day period. You do not need to set up this feature in advance of your call. Certain restrictions apply to retirement accounts. For details, call 1-800-799-7526.
By mail	You may send a signed letter of instruction or, if applicable, stock power form along with any share certificates to be sold to the address below. In your letter of instruction, note the Fund's name, share class, account number, and the dollar value or number of shares you wish to sell. All account owners must sign the letter. Signatures must be guaranteed by either a bank, a member firm of a national stock exchange or another eligible guarantor that participates in the Medallion Signature Guarantee Program for amounts over $100,000 or for alternate payee or mailing instructions. Additional documentation is required for sales by corporations, agents, fiduciaries, surviving joint owners and individual retirement account owners. For details, call 1-800-345-6611. Mail your letter of instruction to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By wire	You may sell Fund shares and request that the proceeds be wired to your bank. You must set up this feature prior to your request. Be sure to complete the appropriate section of the account application for this feature. Generally, the value of your redemption must be at least equal to $500 in order to have the sale proceeds wired to your bank. There is a $7.50 charge for wiring sale proceeds to your bank. (The transfer agent may waive this fee for omnibus and nominee accounts.) Your bank may charge additional fees for such wire transfer.
By systematic withdrawal plan	You may automatically sell a specified dollar amount or percentage of your account on a monthly, quarterly or semiannual basis and have the proceeds sent to you if your account balance is at least $5,000. The $5,000 minimum account balance requirement is waived for wrap accounts. This feature is not available if you hold your shares in certificate form. All dividend and capital gains distributions must be reinvested. Be sure to complete the appropriate section of the account application for this feature.
By electronic funds transfer	You may sell Fund shares and request that the proceeds be electronically transferred to your bank. Proceeds may take up to two business days to be received by your bank. You must set up this feature prior to your request. Be sure to complete the appropriate section of the account application for this feature.
Through the internet	You may sell Fund shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet redemptions. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

FUND POLICY ON TRADING OF FUND SHARES

The interests of the Fund's long-term shareholders may be adversely affected by certain short-term trading activity by Fund shareholders. Such short-term trading activity, when excessive, has the potential to interfere with efficient portfolio management, generate transaction and other costs, dilute the value of Fund shares held by long-term shareholders and have other adverse effects on the Fund. This type of excessive short-term trading activity is referred to herein as "market timing." For purposes of this section, The "Columbia Funds" are The Columbia, Columbia Acorn Trust and Wanger Advisors Trust families of mutual funds. The Columbia Funds are not

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intended as vehicles for market timing. The Board of Trustees of the Fund has adopted the policies and procedures set forth below with respect to frequent trading of the Fund's shares.

The Fund, directly and through its agents, takes various steps designed to deter and curtail market timing. For example, if the Fund detects that any shareholder has conducted two "round trips" (as defined below) in the Fund in any 28-day period, except as noted below with respect to orders received through omnibus accounts, the Fund will reject the shareholder's future purchase orders, including exchange purchase orders, involving any Columbia fund (other than a money market fund). In addition, if the Fund determines that any person, group or account has engaged in any type of market timing activity (independent of the two-round-trip limit), the Fund may, in its discretion, reject future purchase orders by the person, group or account, including exchange purchase orders, involving the same or any other Columbia fund, and also retains the right to modify these market timing policies at any time without prior notice.

The rights of shareholders to redeem shares of the Fund are not affected by any of the limits mentioned above. However, the Fund imposes a redemption fee on the proceeds of Fund shares that are redeemed or exchanged within 60 days of their purchase.

For these purposes, a "round trip" is a purchase by any means into a Columbia fund followed by a redemption, of any amount, by any means out of the same Columbia fund. Under this definition, an exchange into the Fund followed by an exchange out of the Fund is treated as a single round trip. Also for these purposes, where known, accounts under common ownership or control generally will be counted together. Accounts maintained or managed by a common intermediary, such as an adviser, selling agent or trust department, generally will not be considered to be under common ownership or control.

Purchases, redemptions and exchanges made through the Columbia Funds' Automatic Investment Plan, Systematic Withdrawal Plan or similar automated plans are not subject to the two-round-trip limit. Purchases, redemptions and exchanges made by Columbia Thermostat Fund are also not subject to the two-round-trip limit. The two-round-trip limit may be modified for, or may not be applied to, accounts held by certain retirement plans to conform to plan limits, considerations relating to the Employee Retirement Income Security Act of 1974 or regulations of the Department of Labor, and for certain asset allocation or wrap programs.

The practices and policies described above are intended to deter and curtail market timing in the Fund. However, there can be no assurance that these policies, individually or collectively, will be totally effective in this regard because of various factors. In particular, a substantial portion of purchase, redemption and exchange orders are received through omnibus accounts. Omnibus accounts, in which shares are held in the name of an intermediary on behalf of multiple beneficial owners, are a common form of holding shares among financial intermediaries and retirement plans. The Fund typically is not able to identify trading by a particular beneficial owner through an omnibus account, which may make it difficult or impossible to determine if a particular account is engaged in market timing. Consequently, there is the risk that the Fund may not be able to identify, deter or curtail market timing that occurs in the Fund, which ma y result in certain shareholders being able to market time the Fund while the shareholders in the Fund bear the burden of such activities.

Certain financial intermediaries (including certain retirement plan service providers whose clients include, among others, various retirement plans sponsored by Bank of America and its affiliates for the benefit of its employees (the "Bank of America retirement plan service providers")) have different policies regarding monitoring and restricting market timing in the underlying beneficial owner accounts that they maintain through an omnibus account that may be more or less restrictive than the Fund practices discussed above. In particular, the Bank of

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Your Account

America retirement plan service providers permit the reinstatement of future purchase orders for shares of the Fund following various suspension periods. If an intermediary does not enforce the Fund's policy, the intermediary must either provide data transparency to Columbia Management or Columbia Management must determine that the intermediary's policy taken in its entirety provides protections to fund shareholders that are generally commensurate with the Funds privacy policy.

The Fund seeks to act in a manner that it believes is consistent with the best interests of Fund shareholders in making any judgments regarding market timing. Neither the Fund nor its agents shall be held liable for any loss resulting from rejected purchase orders or exchanges.

The Fund will assess, subject to limited exceptions, a 2.00% redemption fee on the proceeds of Fund shares that are redeemed (either by selling shares or exchanging into another Columbia fund) within 60 days of their purchase. The redemption fee is paid to the Fund.

The redemption fee is imposed on Fund shares redeemed (including redemptions by exchange) within 60 days of purchase. In determining which shares are being redeemed, the Fund generally applies a first-in, first-out approach. For Fund shares acquired by exchange, the holding period prior to the exchange will not be considered in determining whether to assess the redemption fee.

The redemption fee will not be imposed if you qualify for a waiver and the Fund has received proper notification, unless the waiver is automatic as noted below. The Fund will redeem any shares that are eligible for a waiver first.

A Fund shareholder won't pay an otherwise applicable redemption fee on any of the following transactions:

•  shares sold following the death or disability (as defined in the tax code) of the shareholder, including a registered joint owner

•  shares sold by or distributions from participant directed retirement plans, such as 401(k), 403(b), 457, Keogh, profit sharing, and money purchase pension accounts, where the Fund does not have access to information about the individual participant account activity, except where the Fund has received an indication that the plan administrator is able to assess the redemption fee to the appropriate accounts (automatic)

•  shares sold by certain investment funds, including those that Columbia Management Advisors, LLC or its affiliates may manage (automatic)

•  shares sold as part of an automatic rebalancing within an asset allocation program or by certain wrap programs where the program sponsor has provided assurances reasonably satisfactory to the Fund that the program is not designed to be a vehicle for market timing

•  shares sold by accounts maintained by a financial institution or intermediary where the Fund has received information reasonably satisfactory to the Fund indicating that the financial institution or intermediary maintaining the account is unable for administrative reasons to assess the redemption fee to underlying shareholders

•  shares sold by an account which has demonstrated a hardship, such as a medical emergency, as determined in the absolute discretion of the Fund

•  shares that were purchased by reinvested dividends (automatic)

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•  shares that are redeemed or exchanged through Columbia funds' Systematic Withdrawal Plan or similar affiliated or unaffiliated automated plans

•  the following retirement plan distributions:

• lump-sum or other distributions from a qualified corporate or self-employed retirement plan following retirement (or following attainment of age 591/2 in the case of a "key employee" of a "top heavy" plan)

• distributions from an individual retirement account (IRA) or Custodial Account under Section 403(b)(7) of the tax code, following attainment of age 591/2

The Fund also has the discretion to waive the 2.00% redemption fee if the Fund is in jeopardy of failing the 90% income test or losing its registered investment company qualification for tax purposes.

As described above, certain intermediaries do not assess redemption fees to certain categories of redemptions that do not present significant market timing concerns (such as automatic withdrawal plan redemptions). In these situations, the Fund's ability to assess redemption fees is generally limited by the intermediary's policies and, accordingly, no redemption fees will be assessed on such redemptions.

OTHER INFORMATION ABOUT YOUR ACCOUNT

How the Fund's Share Price is Determined The price of each class of the Fund's shares is based on its net asset value. The net asset value is determined at the close of regular trading on the NYSE, usually 4:00 p.m. Eastern time, on each business day that the NYSE is open for trading (typically Monday through Friday). Net asset value is not determined on days on which the NYSE is closed for trading.

When you request a transaction, it will be processed at the net asset value per share (plus any applicable sales charges) next determined after your request is received in "good form" by the distributor. In most cases, in order to receive that day's price, the distributor must receive your order before that day's transactions are processed. If you request a transaction through your financial advisor, your financial advisor must receive your order by the close of trading on the NYSE to receive that day's price.

The Fund determines its net asset value for each share class by dividing each class's total net assets by the number of that class's outstanding shares. In determining the net asset value, the Fund must determine the value of each security in its portfolio at the close of each trading day. Because the Fund holds securities that are traded on foreign exchanges, the value of the Fund's securities may change on days when shareholders will not be able to buy or sell Fund shares. This will affect the Fund's net asset value on the day it is next determined. Securities for which market quotations are available are valued each day at the current market value. However, where market quotations are not available, or when the adviser believes that subsequent events have made them unreliable, the Fund may use other data to determine the fair value of the securities.

The Fund has retained an independent statistical fair value pricing service to assist in the fair valuation process for securities principally traded in a foreign market in order to adjust for possible changes in value that may occur between the close of the foreign exchange and the time at which Fund shares are priced. The use of an independent fair value pricing service is intended to and may decrease the opportunities for time zone arbitrage transactions. There can be no assurance that the use of an independent fair value pricing service will successfully decrease arbitrage opportunities. If a security is valued at a "fair value," that value may be different from the last quoted market price for the security.

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You can find the daily prices of some share classes for the Fund in most major daily newspapers under the heading of "Columbia." You can find daily prices for all share classes by visiting www.columbiafunds.com.

Share Certificates Share certificates are not available for any class of shares offered by the Fund. If you currently hold previously issued share certificates, you will not be able to sell your shares until you have returned your share certificates to the transfer agent.

Dividends, Distributions, and Taxes The Fund has the potential to make the following distributions:

Types of Distributions

Dividends	Represents interest and dividends earned from securities held by the Fund, net of expenses incurred by the Fund.
Capital gains	Represents net long-term capital gains on sales of securities held for more than one year and net short-term capital gains, which are gains on sales of securities held for a one-year period or less.

Distribution Options The Fund distributes any dividends in June and December and any capital gains (including short-term capital gains) at least annually. You can choose one of the options listed in the table below for these distributions when you open your account. To change your distribution option call 1-800-345-6611.

If you do not indicate on your application or at the time your account is established your preference for handling distributions, the Fund will automatically reinvest all distributions in additional shares of the Fund.

UNDERSTANDING FUND DISTRIBUTIONS

The Fund may earn income from the securities it holds. The Fund also may realize capital gains or losses on sales of its securities. The Fund intends to distribute substantially all of its net investment income and capital gains to shareholders each year. As a shareholder, you are entitled to a portion of the Fund's income and capital gains based on the number of shares you own at the time these distributions are declared.

Distribution Options

Reinvest all distributions in additional shares of the Fund

Reinvest all distributions in shares of another fund

Receive dividends in cash (see options below) and reinvest capital gains

Receive all distributions in cash (with one of the following options):

• send the check to your address of record

• send the check to a third-party address

• transfer the money to your bank via electronic funds transfer

Distributions of $10 or less will automatically be reinvested in additional Fund shares. If you elect to receive distributions by check and the check is returned as undeliverable, all subsequent distributions will be reinvested in additional shares of the Fund.

Taxes Unless you are an entity exempt from income taxes or invest under a retirement account, regardless of whether you receive your distributions in cash or reinvest them in additional Fund shares, all Fund distributions are subject to federal income tax. Depending on where you live, distributions also may be subject to state and local income taxes.

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The Fund intends to elect to be treated and to qualify each year as a regulated investment company. A regulated investment company is not subject to tax at the corporate level on income and gains from investments that are distributed to shareholders in accordance with applicable law. However, the Fund's failure to qualify as a regulated investment company could result in corporate level taxation, and consequently, a reduction in income available for distribution to shareholders.

In general, any distributions of dividends, interest and short-term capital gains (determined by how long the Fund held the investments that generated them) are taxable as ordinary income, unless such dividends are "qualified dividend income" (as defined in the Internal Revenue Code) eligible for a reduced rate of tax. Properly designated distributions of long-term capital gains (determined by how long the Fund held the investments that generated them) are generally taxable as such, regardless of how long you have held your Fund shares. You will be provided with information each year regarding the amount of ordinary income and capital gains distributed to you for the previous year and any portion of your distribution which is exempt from state and local taxes. The Fund's investments in foreign securities may be subject to foreign withholding taxes. You may be entitled to claim a credit or deduction with respect to foreign taxes. Long-term capital gain rates have been reduced — in general, to 15% with lower rates applying to taxpayers in the 10% and 15% rate brackets — for taxable years beginning before January 1, 2011. Distributions are taxable to you even if they are paid from income or gains earned by the Fund before you made your investment (and thus were included in the price you paid). Your investment in the Fund may have additional personal tax implications. Please consult your tax advisor about foreign, federal, state, local or other applicable tax laws.

In addition to the dividends and capital gains distributions made by the Fund, you may realize a capital gain or loss when selling or exchanging shares of the Fund. Such transactions also may be subject to federal, state and local income tax.

Foreign Income Taxes The Fund may receive investment income from sources within foreign countries, and that income may be subject to foreign income taxes at the source. If the Fund pays non-refundable taxes to foreign governments during the year, the taxes will reduce the Fund's dividends but will still be included in your taxable income. You may be able to claim a credit or deduction on your tax return for your share of foreign taxes paid by the Fund.

Board of Trustees

The Fund is governed by its Board of Trustees. More than 75% of the Fund's Trustees are independent, meaning that they have no affiliation with the adviser or the Funds, apart from their positions as Trustees and the personal investments they may have made as private individuals.

The independent Trustees bring backgrounds in business and the professions and academia to their task of working with the Funds' officers to establish the policies and oversee the activities of the Funds. Among the Trustees' responsibilities are selecting the investment adviser for the Funds; negotiating the advisory agreements; reviewing other contracts; approving investment policies; monitoring Fund operations, performance, and costs; and nominating or selecting new Trustees.

Each Trustee serves until his or her retirement, resignation, death or removal; or otherwise as specified in the Trust's organizational documents. It is expected that every five years the Trustees will call a meeting of shareholders to elect Trustees. A Trustee must retire at the end of the year in which he or she attains the age of 75. Any Trustee may be removed at a shareholders' meeting by a vote representing two-thirds of the net asset value of

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Managing the Fund

all shares of the Funds of the Trust. The mailing address for the Trustees and officers is 227 W. Monroe, Suite 3000, Chicago, Illinois 60606.

For more detailed information on the Board of Trustees, please refer to the SAI.

INVESTMENT ADVISER

Columbia Wanger Asset Management, L.P. (CWAM), located at 227 West Monroe Street, Suite 3000, Chicago, Illinois 60606, is the Fund's investment adviser and is responsible for the Fund's management, subject to the oversight of the Fund's Board of Trustees. CWAM and its predecessor have managed mutual funds, including the Fund, since 1992. In its duties as investment adviser, CWAM runs the Fund's day-to-day business, including making investment decisions and placing all orders for the purchase and sale of the Fund's portfolio securities.

CWAM was previously named Liberty Wanger Asset Management, L.P. and its predecessor was named Wanger Asset Management, L.P. (WAM). CWAM is a wholly owned subsidiary of Columbia Management Group, LLC, which is an indirect wholly owned subsidiary of Bank of America Corporation. As of December 31, 2006, CWAM managed more than $32.9 billion in assets.

CWAM's advisory fee for managing the Fund in 2006 was 0.94% of the Fund's average daily net assets. CWAM also received an administrative fee from the Fund in 2006 of 0.04% of the Fund's average daily net assets. A discussion of the factors considered by the Fund's Board of Trustees in approving the Fund's investment advisory contract is included in the Fund's annual report to shareholders for the period ended December 31, 2006.

PORTFOLIO MANAGER

CWAM uses a team to assist the lead portfolio manager in managing the Fund. Team members share responsibility for providing ideas, information and knowledge in managing the Fund, and each team member has one or more particular areas of expertise. The portfolio manager is responsible for making daily investment decisions and utilizing the management team's input and advice when making buy and sell determinations.

Christopher J. Olson

Lead portfolio manager

Christopher Olson is a vice president of the Trust and has managed Columbia Acorn International Select since September 2001. He has been a member of the international analytical team at CWAM since January 2001. Mr. Olson also is a vice president of Wanger Advisors Trust, a co-portfolio manager of Wanger International Small Cap and the lead portfolio manager of Wanger International Select, two international mutual funds underlying variable insurance products.

The Statement of Additional Information provides additional information about the portfolio manager's compensation, other accounts managed and ownership of securities in the Fund.

LEGAL PROCEEDINGS

The Trust, CWAM and the trustees of the Trust (collectively, the "Columbia defendants") are named as defendants in class and derivative complaints, which were consolidated in a Multi-District Action in the federal district court for the District of Maryland on February 20, 2004 (the "MDL Action"). These lawsuits contend that defendants permitted certain investors to market time their trades in certain Columbia Acorn Funds. The MDL

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Managing the Fund

Action is ongoing. All claims against the Trust and its independent trustees have been dismissed; however, the interested trustees of the Trust are still parties to the MDL Action.

On March 21, 2005, a class action complaint was filed against the Trust in the Superior Court of the Commonwealth of Massachusetts seeking to rescind the contingent deferred sales charges assessed upon redemption of Class B shares of Columbia Acorn Funds due to the alleged market timing by certain shareholders of the Columbia Acorn Funds. In addition to the rescission of sales charges, plaintiffs seek recovery of actual damages, attorneys' fees and costs. The case has been transferred to the MDL Action in the federal district court of Maryland.

The Trust and CWAM are also defendants in a class action lawsuit, filed on November 13, 2003 in the Circuit Court of the Third Judicial Circuit, Madison County, Illinois, that alleges, in summary, that the Trust and CWAM exposed shareholders of Columbia Acorn International to trading by market timers by allegedly (a) failing to properly evaluate daily whether a significant event affecting the value of that fund's securities had occurred after foreign markets had closed but before the calculation of the fund's net asset value; (b) failing to implement the fund's portfolio valuation and share pricing policies and procedures; and (c) failing to know and implement applicable rules and regulations concerning the calculation of net asset value ("Fair Valuation Lawsuit"). On April 5, 2005, the United States Court of Appeals for the Seventh Circuit ruled that the plaintiffs' state law claims were preempted under federal law resulting in the dismissal of plaintiffs' complaint. Plaintiffs appealed the Seventh Circuit's ruling to the United States Supreme Court. On June 15, 2006, the Supreme Court reversed the Seventh Circuit's ruling on jurisdictional grounds, and the case ultimately was remanded to the state court.

On April 4, 2006, the plaintiffs and the Columbia defendants named in the MDL Action executed an agreement in principle intended to fully resolve all of the lawsuits consolidated in the MDL Action as well as the Fair Valuation Lawsuit. The court entered a stay after the parties executed the agreement in principle. The settlement is subject to court approval.

In 2004, CWAM and the trustees of the Columbia Acorn Trust were named as defendants in certain purported shareholder class and derivative actions making claims, including claims under the Investment Company and the Investment Advisers Acts of 1940 and state law. Certain Columbia Acorn Funds were named as nominal defendants. The suits allege, inter alia, that the fees and expenses paid by the funds are excessive and that the funds' advisers and their affiliates inappropriately used fund assets to distribute the funds and for other improper purposes. On March 2, 2005, the actions were consolidated in the Massachusetts federal court as In re Columbia Entities Litigation. The plaintiffs filed a consolidated amended complaint on June 9, 2005. On November 30, 2005, the judge dismissed all claims by plaintiffs and entered final judgment in favor of the defendants. The plaintiffs appealed to the United States Court of Appeals for the First Circuit on December 30, 2005. A stipulation and settlement agreement dated January 19, 2007 was filed in the First Circuit on February 14, 2007, with a joint stipulation of dismissal and motion for remand to obtain district court approval of the settlement. The joint motion was granted and the appeal was dismissed. On March 6, 2007, the case was remanded to the District Court, where the parties will seek court approval of the settlement. The terms of the proposed settlement, if approved, will require payments by the funds' adviser and/or its affiliates, including payment of plaintiffs' attorneys' fees and notice to class members. In the event that the settlement is not approved, the plaintiffs may elect to g o forward with their appeal and no opinion is expressed regarding the likely outcome or financial impact of such an appeal on any fund.

On or about January 11, 2005, a putative class action lawsuit was filed in federal district court in Massachusetts against the Trust and its trustees, along with Columbia Management Advisors, LLC, the sub-administrator of the Wanger Advisors Funds and the Columbia Acorn Funds. The plaintiffs allege that the defendants failed to submit

24

Managing the Fund

Proof of Claims in connection with settlements of securities class action lawsuits filed against companies in which the Columbia Acorn Funds held positions. The complaint seeks compensatory and punitive damages, and the disgorgement of all fees paid to Columbia Management Advisors, LLC. Plaintiffs have voluntarily dismissed the Trust and its independent trustees.

The Trust and CWAM intend to defend these suits vigorously.

As a result of these matters or any adverse publicity or other developments resulting from them, there may be increased redemptions or reduced sales of Fund shares, which could increase transaction costs or operating expenses, or have other adverse consequences for the Fund.

However, based on currently available information, the Trust believes that the likelihood that these lawsuits will have a material adverse impact on any fund is remote, and CWAM believes that the lawsuits are not likely to materially affect its ability to provide investment management services to the Fund.

Other Investment Strategies and Risks

The Fund's principal investment strategies and associated risks are described under "The Fund — Principal Investment Strategies" and "The Fund — Principal Investment Risks." This section describes other investments the Fund may make and the risks associated with them. In seeking to achieve its investment goal, the Fund may invest in various types of securities and engage in various investment techniques, which are not the principal focus of the Fund and therefore are not described in this prospectus. These types of securities and investment practices and their associated risks are identified and discussed in the Fund's SAI, which you may obtain free of charge (see back cover). The adviser may elect not to buy any of these securities or use any of these techniques. The Fund may not always achieve its investment goal. Except as otherwise noted, approval by the Fund's shareholders is not required to modify or change the F und's investment strategies.

THE INFORMATION EDGE

The Fund generally invests in entrepreneurially managed small- and mid-sized companies that it believes are not as well known by financial analysts and whose position in a niche creates the opportunity for superior earnings-growth potential. CWAM may identify what it believes are important economic, social or technological trends (for example, the growth of outsourcing as a business strategy, or the productivity gains from the increasing use of technology) and try to identify companies it thinks will benefit from these trends.

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Other Investment Strategies and Risks

In making investments for the Fund, CWAM relies primarily on independent, internally generated research to uncover companies that may be less well known than the more popular names. To find these companies, CWAM compares growth potential, financial strength and fundamental value among companies.

Growth Potential	Financial Strength	Fundamental Value
• superior technology • innovative marketing • managerial skill • market niche • good earnings prospects • strong demand for product	• low debt • adequate working capital • conservative accounting practices • adequate profit margin	• reasonable stock price relative to growth potential and financial strength • valuable assets
The realization of this growth potential would likely produce superior performance that is sustainable over time.	A strong balance sheet gives management greater flexibility to pursue strategic objectives and is important to maintaining a competitive advantage.	Once CWAM uncovers an attractive company, it identifies a price that it believes would also make the stock a good value.

LONG-TERM INVESTING

CWAM's analysts continually screen companies and make contact with more than 1,000 companies around the globe each year. To accomplish this, CWAM analysts often talk directly to top management, vendors, suppliers and competitors.

In managing the Fund, CWAM tries to maintain lower taxes and transaction costs by investing with a long-term time horizon (at least two to five years). However, securities purchased on a long-term basis may be sold within 12 months after purchase due to changes in the circumstances of a particular company or industry, or changes in general market or economic conditions.

DERIVATIVE STRATEGIES

The Fund may enter into a number of derivative strategies, including those that employ futures, options, straddles or similar transactions, to gain or reduce exposure to particular securities or markets. These strategies, commonly referred to as derivatives, involve the use of financial instruments whose values depend on, or are derived from, the value of an underlying security, index or currency. The Fund may use these strategies to adjust the Fund's sensitivity to changes in interest rates, or for other hedging purposes (i.e., attempting to offset a potential loss in one position by establishing an interest in an opposite position). Derivative strategies involve the risk that they may exaggerate a loss, potentially losing more money than the actual cost of the underlying security, or limit a potential gain. Also, with some derivative strategies there is a risk that the other party to the transaction may fail to honor its contr act terms, causing a loss to the Fund or that the Fund may not be able to find a suitable derivative transaction counterparty, and thus may be unable to invest in derivatives altogether.

TEMPORARY DEFENSIVE STRATEGIES

At times, CWAM may determine that adverse market conditions make it desirable to temporarily suspend the Fund's normal investment activities. During such times, the Fund may, but is not required to, invest in cash or high-quality, short-term debt securities, without limit. Taking a temporary defensive position may prevent the Fund from achieving its investment goal.

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Financial Highlights

The financial highlights table is intended to help you understand the Fund's financial performance. Information is shown for the Fund's last five fiscal years, which run from January 1 to December 31. Certain information in the table reflects the financial results for a single Class A, B or C share. The total returns in the table represent the return that you would have earned (or lost) on an investment in the Fund (assuming reinvestment of all dividends and distributions). This information has been derived from the Fund's financial statements, which have been audited for the years ended December 31, 2004, 2005 and 2006 by PricewaterhouseCoopers LLP, an independent registered public accounting firm, whose report, along with the Fund's financial statements, is included in the Fund's annual report. The information for the years ended December 31, 2002 and 2003 is included in the Fund's financial statements that have been audited a nother independent registered public accounting firm, whose report expressed an unqualified opinion on those financial statements and highlights. You can request a free annual report containing those financial statements by calling 1-800-345-6611.

Columbia Acorn International Select

	Year ended December 31,
	2006			2005			2004			2003		2002
	Class A			Class A			Class A			Class A		Class A
Net asset value — Beginning of period ($)		20.36			17.85			14.45			10.24		12.07
Income from Investment Operations ($):
Net investment income (loss)(a)		0.03			0.06			(0.00	)(b)		0.03		(0.01	)
Net realized and unrealized gain (loss)		7.29			2.69			3.43			4.18		(1.82	)
Total from Investment Operations		7.32			2.75			3.43			4.21		(1.83	)
Less Distributions Declared to Shareholders ($):
From net investment income		—	(b)		(0.24	)		(0.03	)		—		—
Total Distributions Declared to Shareholders		—	(b)		(0.24	)		(0.03	)		—		—
Net asset value — End of period ($)		27.68			20.36			17.85			14.45		10.24
Total return (%)(c)(d)		35.97			15.60			23.76			41.11		(15.16	)
Ratios to Average Net Assets/Supplemental Data (%):
Expenses(e)		1.58			1.70			1.75			1.80		1.80
Net investment income (loss)(e)		0.11			0.34			(0.03	)		0.24		(0.09	)
Waiver/reimbursement		0.02			0.10			0.37			0.44		0.33
Portfolio turnover rate (%)		47			39			73			69		102
Net assets at end of period (000's) ($)		22,599			10,219			4,357			2,557		2,612

(a)  Per share data was calculated using average shares outstanding during the period.

(b)  Rounds to less than $(0.01) per share.

(c)  Total return at net asset value assuming all distributions reinvested and no initial sales charge or contingent deferred sales charge.

(d)  Had the investment adviser and/or transfer agent not waived and/or reimbursed a portion of expenses, total return would have
been reduced.

(e)  The benefits derived from custody fees paid indirectly had no impact.

27

Financial Highlights

Columbia Acorn International Select

	Year ended December 31,
	2006			2005			2004			2003			2002
	Class B			Class B			Class B			Class B			Class B
Net asset value — Beginning of period ($)		19.80			17.36			14.12			10.08			11.96
Income from Investment Operations ($):
Net investment loss(a)		(0.12	)		(0.03	)		(0.10	)		(0.06	)		(0.08	)
Net realized and unrealized gain (loss)		7.05			2.61			3.34			4.10			(1.80	)
Total from Investment Operations		6.93			2.58			3.24			4.04			(1.88	)
Less Distributions Declared to Shareholders ($):
From net investment income		—			(0.14	)		—			—			—
Total Distributions Declared to Shareholders		—			(0.14	)		—			—			—
Net asset value — End of period ($)		26.73			19.80			17.36			14.12			10.08
Total return (%)(b)(c)		35.00			14.97			22.95			40.08			(15.72	)
Ratios to Average Net Assets/Supplemental Data (%):
Expenses(d)		2.25			2.30			2.38			2.45			2.45
Net investment loss(d)		(0.53	)		(0.16	)		(0.66	)		(0.52	)		(0.74	)
Waiver/reimbursement		0.04			0.28			0.58			0.44			0.33
Portfolio turnover rate (%)		47			39			73			69			102
Net assets at end of period (000's) ($)		9,787			6,594			5,097			3,162			1,835

(a)  Per share data was calculated using average shares outstanding during the period.

(b)  Total return at net asset value assuming all distributions reinvested and no initial sales charge or contingent deferred sales charge.

(c)  Had the investment adviser and/or transfer agent not waived and/or reimbursed a portion of expenses, total return would have
been reduced.

(d)  The benefits derived from custody fees paid indirectly had no impact.

28

Financial Highlights

Columbia Acorn International Select

	Year ended December 31,
	2006			2005			2004			2003			2002
	Class C			Class C			Class C			Class C			Class C
Net asset value — Beginning of period ($)		19.80			17.38			14.14			10.09			11.97
Income from Investment Operations ($):
Net investment loss(a)		(0.15	)		(0.05	)		(0.11	)		(0.05	)		(0.08	)
Net realized and unrealized gain (loss)		7.05			2.60			3.35			4.10			(1.80	)
Total from Investment Operations		6.90			2.55			3.24			4.05			(1.88	)
Less Distributions Declared to Shareholders ($):
From net investment income		—			(0.13	)		—			—			—
Total Distributions Declared to Shareholders		—			(0.13	)		—			—			—
Net asset value — End of period ($)		26.70			19.80			17.38			14.14			10.09
Total return (%)(b)(c)		34.85			14.77			22.91			40.14			(15.71	)
Ratios to Average Net Assets/Supplemental Data (%):
Expenses(d)		2.38			2.45			2.45			2.45			2.45
Net investment loss(d)		(0.67	)		(0.30	)		(0.73	)		(0.41	)		(0.74	)
Waiver/reimbursement		0.02			0.17			0.35			0.44			0.33
Portfolio turnover rate (%)		47			39			73			69			102
Net assets at end of period (000's) ($)		7,060			4,083			2,543			3,691			2,915

(a)  Per share data was calculated using average shares outstanding during the period.

(b)  Total return at net asset value assuming all distributions reinvested and no initial sales charge or contingent deferred sales charge.

(c)  Had the investment adviser and/or transfer agent not waived and/or reimbursed a portion of expenses, total return would have
been reduced.

(d)  The benefits derived from custody fees paid indirectly had no impact.

29

APPENDIX

Hypothetical Investment and Expense Information

The Fund is required to disclose the following supplemental hypothetical investment information, which provides additional information about the effect of the expenses paid by the Fund, including investment advisory fees and other Fund costs, on the Fund's returns over a 10-year period. The tables show the estimated expenses that would be charged on a hypothetical investment of $10,000 in each class of the Fund assuming a 5% return each year, the cumulative return after fees and expenses, and the hypothetical year-end balance after fees and expenses. The tables also assume that all dividends and distributions are reinvested and that Class B shares convert to Class A shares after eight years. The annual expense ratios used for the Fund, which are the same as those stated in the Annual Fund Operating Expenses table, are presented in the tables and are net of any contractual fee waivers or expense reimbursements for the period of t he contractual commitment. Your actual costs may be higher or lower. The tables shown below reflect the maximum initial sales charge for Class A shares but do not reflect any contingent deferred sales charges which may be payable on redemption. If contingent deferred sales charges were reflected, the "Hypothetical Year-End Balance After Fees and Expenses" amounts shown would be lower and the "Annual Fees and Expenses" amounts shown would be higher.

Columbia Acorn International Select — Class A Shares

Maximum Sales Charge 5.75%					Initial Hypothetical Investment Amount $10,000.00						Assumed Rate of Return 5%
Year		Cumulative Return Before Fees & Expenses			Annual Expense Ratio			Cumulative Return After Fees & Expenses			Hypothetical Year-End Balance After Fees & Expenses		Annual Fees & Expenses(1)
	1		5.00	%		1.63	%		-2.57	%(2)	$	9,742.62	$	731.22
	2		10.25	%		1.63	%		0.71	%	$	10,070.95	$	161.48
	3		15.76	%		1.63	%		4.10	%	$	10,410.34	$	166.92
	4		21.55	%		1.63	%		7.61	%	$	10,761.17	$	172.55
	5		27.63	%		1.63	%		11.24	%	$	11,123.82	$	178.36
	6		34.01	%		1.63	%		14.99	%	$	11,498.69	$	184.37
	7		40.71	%		1.63	%		18.86	%	$	11,886.20	$	190.59
	8		47.75	%		1.63	%		22.87	%	$	12,286.76	$	197.01
	9		55.13	%		1.63	%		27.01	%	$	12,700.83	$	203.65
	10		62.89	%		1.63	%		31.29	%	$	13,128.85	$	210.51
Total Gain After Fees and Expenses											$	3,128.85
Total Annual Fees and Expenses													$	2,396.66

(1)  Annual Fees and Expenses are calculated based on the average between the beginning and ending balance for each year. All information is calculated on an annual compounding basis.

(2)  Reflects deduction of the maximum initial sales charge.

30

Appendix

Columbia Acorn International Select — Class B Shares

Maximum Sales Charge 0.00%					Initial Hypothetical Investment Amount $10,000.00						Assumed Rate of Return 5%
Year		Cumulative Return Before Fees & Expenses			Annual Expense Ratio			Cumulative Return After Fees & Expenses			Hypothetical Year-End Balance After Fees & Expenses		Annual Fees & Expenses(1)
	1		5.00	%		2.23	%		2.77	%	$	10,277.00	$	226.09
	2		10.25	%		2.23	%		5.62	%	$	10,561.67	$	232.35
	3		15.76	%		2.23	%		8.54	%	$	10,854.23	$	238.79
	4		21.55	%		2.23	%		11.55	%	$	11,154.89	$	245.40
	5		27.63	%		2.23	%		14.64	%	$	11,463.88	$	252.20
	6		34.01	%		2.23	%		17.81	%	$	11,781.43	$	259.19
	7		40.71	%		2.23	%		21.08	%	$	12,107.78	$	266.36
	8		47.75	%		2.23	%		24.43	%	$	12,443.16	$	273.74
	9		55.13	%		1.63	%		28.62	%	$	12,862.50	$	206.24
	10		62.89	%		1.63	%		32.96	%	$	13,295.97	$	213.19
Total Gain After Fees and Expenses											$	3,295.97
Total Annual Fees and Expenses													$	2,413.55

(1)  Annual Fees and Expenses are calculated based on the average between the beginning and ending balance for each year. All information is calculated on an annual compounding basis.

31

Appendix

Columbia Acorn International Select — Class C Shares

Maximum Sales Charge 0.00%					Initial Hypothetical Investment Amount $10,000.00						Assumed Rate of Return 5%
Year		Cumulative Return Before Fees & Expenses			Annual Expense Ratio			Cumulative Return After Fees & Expenses			Hypothetical Year-End Balance After Fees & Expenses		Annual Fees & Expenses(1)
	1		5.00	%		2.42	%		2.58	%	$	10,258.00	$	245.12
	2		10.25	%		2.42	%		5.23	%	$	10,522.66	$	251.45
	3		15.76	%		2.42	%		7.94	%	$	10,794.14	$	257.93
	4		21.55	%		2.42	%		10.73	%	$	11,072.63	$	264.59
	5		27.63	%		2.42	%		13.58	%	$	11,358.30	$	271.41
	6		34.01	%		2.42	%		16.51	%	$	11,651.35	$	278.42
	7		40.71	%		2.42	%		19.52	%	$	11,951.95	$	285.60
	8		47.75	%		2.42	%		22.60	%	$	12,260.31	$	292.97
	9		55.13	%		2.42	%		25.77	%	$	12,576.63	$	300.53
	10		62.89	%		2.42	%		29.01	%	$	12,901.11	$	308.28
Total Gain After Fees and Expenses											$	2,901.11
Total Annual Fees and Expenses													$	2,756.30

(1)  Annual Fees and Expenses are calculated based on the average between the beginning and ending balance for each year. All information is calculated on an annual compounding basis.

32

Notes

33

Notes

34

FOR MORE INFORMATION

Additional information about the Fund's investments is available in the Fund's semiannual and annual reports to shareholders. The annual report contains a discussion of the market conditions and investment strategies that significantly affected the Fund's performance during its last fiscal year.

You may wish to read the SAI for more information on the Fund and the securities in which it invests. The SAI is incorporated into this prospectus by reference, which means that it is considered to be part of this prospectus.

You can get free copies of annual and semiannual reports and the SAI, request other information and discuss your questions about the Fund by visiting www.columbiafunds.com or by writing or calling the Fund's transfer agent at:

Columbia Management Services, Inc.
P.O. Box 8081
Boston, MA 02266-8081
1-800-345-6611

Text-only versions of all Fund documents can be viewed online or downloaded from the EDGAR database on the Securities and Exchange Commission internet site at www.sec.gov.

You can review and copy information about the Fund, including the SAI, by visiting the following location, and you can obtain copies upon payment of a duplicating fee, by electronic request at the e-mail address publicinfo@sec.gov or by writing the:

Public Reference Room
Securities and Exchange Commission
Washington, DC 20549-0102

Information on the operation of the Public Reference Room may be obtained by calling 1-202-942-8090.

Investment Company Act file number:
Columbia Acorn Trust: 811-01829
•  Columbia Acorn International Select

©2007 Columbia Management Distributors, Inc.
One Financial Center, Boston, MA 02111-2621
800.426.3750 www.columbiafunds.com

INT-36/130113-0507

Columbia^SM

Acorn International Select^SM  Prospectus, May 1, 2007

Class Z Shares

Advised by Columbia Wanger Asset Management, L.P.

TABLE OF CONTENTS

THE FUND	2
Investment Goal	2
Principal Investment Strategies	2
Principal Investment Risks	2
Portfolio Holdings Disclosure	4
Performance History	4
Your Expenses	6
YOUR ACCOUNT	8
How to Buy Shares	8
Eligible Investors	9
Sales Charges (Commissions)	11
How to Exchange Shares	11
How to Sell Shares	12
Fund Policy on Trading of Fund Shares and Redemption Fees	13
Financial Intermediary Payments	16
Other Information About Your Account	17
BOARD OF TRUSTEES	19
MANAGING THE FUND	20
Investment Adviser	20
Portfolio Manager	20
Legal Proceedings	20
OTHER INVESTMENT STRATEGIES AND RISKS	23
The Information Edge	23
Long-Term Investing	23
Derivative Strategies	24
Temporary Defensive Strategies	24
FINANCIAL HIGHLIGHTS	25
APPENDIX	26

Only eligible investors may purchase Class Z shares. See "Your Account — Eligible Investors" for more information.

Although these securities have been registered with the Securities and Exchange Commission, the Commission has not approved or disapproved any shares offered in this prospectus or determined whether this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Acorn International Select is a trademark owned and registered by Columbia Acorn Trust, Columbia, Columbia Management^® and Columbia Management Services, Inc. are service marks owned and/or registered by Bank of America

The Fund

INVESTMENT GOAL

Columbia Acorn International Select (Acorn International Select^SM) seeks long-term growth of capital.

PRINCIPAL INVESTMENT STRATEGIES

Acorn International Select generally invests in the stocks of companies based in developed markets (for example, Japan, Canada and the United Kingdom) outside the United States. The Fund invests in at least three countries. The Fund is a diversified fund that takes advantage of its adviser's research and stock-picking capabilities to invest in a limited number of foreign companies (between 40-60), offering the potential to provide above-average growth over time. The Fund invests primarily in companies with market capitalizations of $2 to $25 billion at the time of initial purchase. Although the Fund primarily invests in small- and medium sized companies, at times the Fund may invest in larger-sized companies.

Acorn International Select believes that companies within this capitalization range, which are not as well known by financial analysts, may offer higher return potential than the stocks of companies with capitalizations above $25 billion.

Acorn International Select typically looks for companies with:

•  A strong business franchise that offers growth potential.

•  Products and services that give the company a competitive advantage.

•  A stock price the Fund's investment adviser believes is reasonable relative to the assets and earning power of the company.

Acorn International Select is an international fund and, under normal circumstances, invests at least 65% of its net assets (plus any borrowings for investment purposes) in the stocks of foreign companies based in developed markets outside the United States.

Additional strategies that are not principal investment strategies and the risks associated with them are described later in this prospectus under "Other Investment Strategies and Risks."

PRINCIPAL INVESTMENT RISKS

The principal risks of investing in the Fund are described below. There are many circumstances (including additional risks that are not described here) that could prevent the Fund from achieving its investment goal. You may lose money by investing in the Fund.

Management risk means that the adviser's investment decisions might produce losses or cause the Fund to underperform when compared to other funds with a similar investment goal. Market risk means that security prices in a market, sector or industry may fall, reducing the value of your investment. Because of management and market risk, there is no guarantee that the Fund will achieve its investment goal or perform favorably among comparable funds.

Since the Fund purchases equity securities, it is subject to equity risk. This is the risk that stock prices will fall over short or extended periods of time. Although the stock market historically has outperformed other asset classes over the long term, the stock market tends to move in cycles. Individual stock prices may fluctuate drastically from day-to-day and may underperform other asset classes over an extended period of time. Individual companies may report poor results or be negatively affected by industry and/or economic trends and

2

The Fund

developments. The prices of securities issued by such companies may suffer a decline in response. These price movements may result from factors affecting individual companies, industries or the securities market as a whole.

Because the Fund invests in stocks, the price of its shares — its net asset value (NAV) per share — fluctuates daily in response to changes in the market value of stocks.

Sector risk is inherent in the Fund's investment strategy. Companies that are in different but closely related industries are sometimes described as being in the same broad economic sector. The values of stocks of different companies in a market sector may be similarly affected by particular economic or market events. Although the Fund does not intend to focus on any particular sector, at times the Fund may have a large portion of its assets invested in a particular sector.

Foreign securities are subject to special risks. Foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the dollar value of foreign securities denominated in foreign currencies and U.S. dollars, without a change in the intrinsic value of those securities. The liquidity of foreign securities may be more limited than that of domestic securities, which means that the Fund may, at times, be unable to sell foreign securities at desirable prices. Brokerage commissions, custodial fees and other fees are generally higher for foreign investments. In addition, foreign governments may impose withholding taxes that would reduce the amount of income and capital gains available to distribute to shareholders. Other risks include possible delays in the settlement of transactions or in the notification of income; less publicly av ailable information about companies; the impact of political, social or diplomatic events; possible seizure, expropriation or nationalization of the company or its assets; and possible imposition of currency exchange controls.

Market timers. Because the Fund invests predominantly in foreign securities, the Fund may be particularly susceptible to market timers. Market timers generally attempt to take advantage of the way the Fund prices its shares by trading based on market information they expect will lead to a change in the Fund's net asset value on the next pricing day. Market timing activity may be disruptive to Fund management and, since a market timer's profits are effectively paid directly out of the Fund's assets, may negatively impact the investment returns of other shareholders. Although the Fund has adopted certain policies and methods intended to identify and discourage frequent trading based on this strategy, it cannot ensure that all such activity can be identified or terminated.

Investments in emerging markets are subject to additional risk. The risks of foreign investments are typically increased in less developed countries, which are sometimes referred to as emerging markets. For example, political and economic structures in these countries may be new and developing rapidly, which may cause instability. These countries are also more likely to experience high levels of inflation, deflation or currency devaluations, which could hurt their economies and securities markets.

Small- or mid-cap companies may be more susceptible to market downturns, and their prices could be more volatile than large-cap companies. These companies are more likely than larger companies to have limited product lines, operating histories, markets or financial resources. They may depend heavily on a small management team and may trade less frequently, may trade in smaller volumes and may fluctuate more sharply in price than stocks of larger companies. In addition, such companies may not be widely followed by the investment community, which can lower the demand for their stocks.

An investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

3

The Fund

PORTFOLIO HOLDINGS DISCLOSURE

A description of the Fund's policies and procedures with respect to the disclosure of its portfolio securities is available in the Fund's Statement of Additional Information (SAI), which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611.

The Fund posts its complete portfolio holdings at as of month-end www.columbiafunds.com approximately 30-40 calendar days after such month-end. Additionally, the Fund discloses its top 15 month-end portfolio holdings at www.columbiafunds.com on or about 15 calendar days following such month-end.

Once posted, the above information will remain available on the website until at least the date on which the Fund files a Form N-CSR or Form N-Q for the period that includes the date as of which the information is current.

PERFORMANCE HISTORY

The bar chart below shows the Fund's calendar-year total returns (before taxes) for its Class Z shares. The performance table following the bar chart shows how the Fund's average annual total returns for Class Z shares compare with a broad measure of market performance for one year, five years and the life of the share class. The chart and table are intended to illustrate some of the risks of investing in the Fund by showing changes in the Fund's performance from year to year. All returns include the reinvestment of dividends and distributions. Performance results include the effect of expense reduction arrangements. If these arrangements had not been in place, then performance would have been lower. Any expense reduction arrangements may be discontinued at any time. As with all mutual funds, past performance (before and after taxes) does not predict the Fund's future performance.

UNDERSTANDING PERFORMANCE

Calendar Year Total Returns show the Fund's Class Z share performance for each completed calendar year since the Fund commenced operations. Those returns include the effects of Fund expenses.

Average Annual Total Returns are a measure of the Fund's Class Z average performance over the past one year, five years and life of the share class. They include the effects of Fund expenses.

The Fund's returns are compared to the S&P/Citigroup World ex-U.S. Cap Range $2-10 Billion Index (S&P/Citigroup Cap Range $2-10B). The S&P/Citigroup Cap Range $2-10B is Citigroup's two to ten billion U.S. dollar security market subset of its Broad Market Index. It represents a midcap developed market index, excluding the U.S. Unlike the Fund, an index is not an investment, does not incur fees, expenses or taxes, and is not professionally managed.

4

The Fund

Calendar Year Total Returns (Class Z)⁽¹⁾

(1)  The Fund's performance in 1999 was achieved during a period of unusual market conditions.

For the periods shown in bar chart:
Best quarter: 4th quarter 1999, +46.65%
Worst quarter: 3rd quarter 2001, -22.80%

After tax returns are calculated using the highest historical individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on each investor's own tax situation and may differ from those shown. After-tax returns may not be relevant to investors who hold Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Annual Total Returns — for periods ended December 31, 2006

Share Class	1 Year		5 Years		Life of the Share Class(1)(2)
Class Z (%)
Return Before Taxes		36.27		18.81		14.07
Return After Taxes on Distributions		36.16		18.81		14.00
Return After Taxes on Distributions and Sale of Fund Shares		23.56		16.73		12.60
Index
S&P/Citigroup Cap Range $2-10B (%)		27.88		21.24		12.81	(3)

(1)  The Fund's performance during 1999 was achieved in a period of unusual market conditions.

(2)  The inception date for Class Z shares is November 23, 1998.

(3)  Performance information is from November 30, 1998.

5

The Fund

YOUR EXPENSES

Expenses are one of several factors to consider before you invest in a mutual fund. The tables below describe the fees and expenses you may pay when you buy, hold and sell shares of the Fund.

UNDERSTANDING EXPENSES

Annual Fund Operating Expenses are paid by the Fund. They include management and administration fees and other expenses that generally include, but are not limited to, transfer agency, custody, and legal fees as well as costs related to state registration and printing of Fund documents. The specific fees and expenses that make up the Fund's other expenses will vary from time to time and may include fees or expenses not described here. The Fund will likely incur portfolio transaction costs that are in addition to the total annual fund operating expenses disclosed in the fee table. These transaction costs are made up of all costs that are associated with trading securities for the Fund's portfolio and include, but are not limited to, brokerage commissions and market spreads, as well as potential changes to the price of a security due to the Fund's effor ts to purchase or sell it. While certain elements of transaction costs are readily identifiable and quantifiable, other elements that can make up a significant amount of the Fund's transaction costs are not. Higher transaction costs reduce the Fund's returns.

Shareholder Fees (commissions paid directly from your investment)

Maximum sales charge (load) on purchases (%) (as a percentage of the offering price)	None
Maximum deferred sales charge (load) on redemptions (%) (as a percentage of the lesser of purchase price or redemption price)	None
Redemption fee (%) (as a percentage of amount redeemed, if applicable)	2.00	(1)(2)

(1)  Charged only when selling or exchanging shares you have owned for 60 days or less. For more information, see "Fund Policy on Trading of Fund Shares and Redemption Fees."

(2)  There is a $7.50 charge for wiring sale proceeds to your bank.

Annual Fund Operating Expenses (deducted directly from Fund assets)

Management fees(1) (%)	0.94
Distribution and service (12b-1) fees (%)	None
Other expenses(2) (%)	0.34
Total annual fund operating expenses(3) (%)	1.28

(1)  The Fund pays an investment advisory fee of 0.94%. In addition to the management fee, the Fund and the other funds of Columbia Acorn Trust (the "Trust") pay the adviser an administrative fee based on the average daily aggregate net assets of the Trust at the following annual rates: 0.05% of net assets up to $8 billion; 0.04% of the next $8 billion; and 0.03% of net assets in excess of $16 billion. Based on the Trust's average daily net assets as of December 31,2006, the administrative fee would be at a rate of 0.04% and is included in "Other expenses."

(2)  "Other expenses" have been restated to reflect contractual changes to the transfer agency fees paid by the Fund.

(3)  The Fund's adviser has voluntarily agreed to reimburse the Fund for any ordinary operating expenses (exclusive of distribution and service fees, interest, taxes and extraordinary expenses, if any) exceeding the annual rate of 1.45% of the average daily net assets for Class Z shares. This arrangement may be modified or terminated by either the Fund or its adviser on 30 days notice.

6

The Fund

Example Expenses help you compare the cost of investing in the Fund to the cost of investing in other mutual funds. The table does not take into account any expense reduction arrangements discussed in the footnotes to the Annual Fund Operating Expenses table. It uses the following hypothetical conditions:

•  $10,000 initial investment

•  5% total return for each year

•  Fund operating expenses remain the same

•  Reinvestment of all dividends and distributions

Example Expenses for a $10,000 investment (your actual costs may be higher or lower)

1 Year		3 Years		5 Years		10 Years
$	130	$	406	$	702	$	1,545

See the Appendix for additional hypothetical investment and expense information.

7

Your Account

HOW TO BUY SHARES

If you are an eligible investor (described on page 9), when the Fund receives your purchase request in "good form," your shares will be bought at the next calculated price. "Good form" means that the Fund's transfer agent has all information and documentation it deems necessary to effect your order. For example "good form" may mean that you have properly placed your order with Columbia Management Services, Inc. or your financial advisor or the Fund's transfer agent has received your completed application, including all necessary signatures. The Fund reserves the right to refuse a purchase order for any reason, including if the Fund believes that doing so would be in the best interest of the Fund and its shareholders. The USA PATRIOT Act may require us to obtain certain personal information from you that we will use to verify your identity. If you do not provide the information, we may not be able to open your account. If we are unable to verify your customer information, we reserve the right to close your account or take such other steps as we deem reasonable.

You or your financial advisor may acquire shares of the Fund for your account by exchanging shares you own in a different fund distributed by Columbia Management Distributors, Inc. for shares of the same class or Class A of the Fund at no additional cost. To exchange by telephone, call 1-800-422-3737. Please see "How to Exchange Shares" for more information.

Outlined below are the various options for buying shares:

Method	Instructions
Through your financial advisor	Your financial advisor can help you establish your account and buy Fund shares on your behalf. To receive the current trading day's price, your financial advisor must receive your request prior to the close of regular trading on the New York Stock Exchange (NYSE), usually 4:00 p.m. Eastern time. Your financial advisor may charge you fees for executing the purchase for you.
By check (new account)	For new accounts, send a completed application and check made payable to the Fund to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By check (existing account)	For existing accounts, fill out and return the additional investment stub included in your account statement, or send a letter of instruction including the name, Fund share class and account number with a check made payable to the Fund and mailed to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By exchange	You may acquire Fund shares for your account by exchanging shares you own in a different fund distributed by Columbia Management Distributors, Inc. for shares of the same class or Class A shares of the Fund at no additional cost. To exchange by telephone, call 1-800-422-3737. Please see "How to Exchange Shares" for more information.
By wire	You may purchase Fund shares by wiring money from your bank account to your Fund account. To wire funds to your Fund account, call 1-800-422-3737 for wiring instructions.
By electronic funds transfer	You may purchase Fund shares by electronically transferring money from your bank account to your Fund account by calling 1-800-422-3737. An electronic funds transfer may take up to two business days to settle and must be considered in "good form." You must set up this feature prior to your telephone request. Be sure to complete the appropriate section of the application for this feature.
Automatic investment plan	You may make monthly or quarterly investments ($50 minimum) automatically from your bank account to your Fund account. You may select a pre-authorized amount to be sent via electronic funds transfer. Be sure to complete the appropriate section of the application for this feature.
Automated dollar cost averaging	You may purchase Fund shares for your account by exchanging $100 or more each month from another fund for shares of the same class of the Fund at no additional cost. Exchanges will continue so long as your fund balance is sufficient to complete the transfers. You may terminate your program or change the amount of the exchange (subject to the $100 minimum) by calling 1-800-345-6611. Be sure to complete the appropriate section of the account application for this feature.

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Method	Instructions
By dividend diversification	You may automatically invest dividends distributed by another fund into the same class of shares of the Fund at no additional sales charge. There may be an additional sales charge if automatically investing dividends from a money market fund. To invest your dividends in the Fund, call 1-800-345-6611.
Through the internet	You may purchase Fund shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet purchases. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

ELIGIBLE INVESTORS

Only certain eligible investors may purchase Class Z shares of the Fund (Eligible Investor), directly or by exchange. Please read the following section for a more detailed description of the eligibility requirements. The Eligible Investors described below are subject to different minimum initial investment requirements.

Eligibility for certain waivers, exemptions or share classes by new or existing investors may not be readily available or accessible through all intermediaries or all types of accounts offered by a broker-dealer, bank, third- party administrator or other financial institution (each commonly referred to as an "intermediary"). Accessibility of these waivers through a particular intermediary also may change at any time. If you believe you are eligible to purchase shares under a specific exemption, but are not permitted by your intermediary to do so, please contact your intermediary. You may be asked to provide information, including account statements and other records, regarding your eligibility.

Eligible Investors and their applicable investment minimums are as follows:

No minimum initial investment

•  Any group retirement plan, holding Fund shares in an omnibus manner, for which an intermediary or other entity provides services and is not compensated by the Funds for those services, other than payments for shareholder servicing or sub-accounting performed in place of the transfer agent.

•  Any person investing all or part of the proceeds of a distribution, rollover or transfer of assets into a Columbia Management Individual Retirement Account from any deferred compensation plan which was a shareholder of any of the funds of Columbia Acorn Trust (formerly named Liberty Acorn Trust) on September 29, 2000, in which the investor was a participant and through which the investor invested in one or more of the funds of Columbia Acorn Trust immediately prior to the distribution, transferor rollover.

$1,000 minimum initial investment (by purchase, exchange or transfer)

•  Any individual retirement account of an Eligible Investor; or

•  Any group retirement plan, not holding Fund shares in an omnibus manner, for which an intermediary or other entity provides services and is not compensated by the Fund for those services, other than compensation for shareholder servicing or sub-accounting performed in place of the transfer agent.

$2,500 minimum initial investment (by purchase, exchange or transfer)

•  Any shareholder (as well as any family member of a shareholder or person listed on an account registration for any account of the shareholder) of a fund distributed by Columbia Management Distributors, Inc. (CMD) (i) who holds Class Z shares; (ii) who holds shares issued upon conversion of

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Primary A shares held prior to August 22, 2005; (iii) who holds Class A shares that were obtained by exchange of Class Z shares; or (iv) who holds no-load shares issued upon the merger of a fund distributed by CMD;

•  Any trustee or director (or family member of a trustee or director) of any fund distributed by CMD;

•  Any employee (or family member of an employee) of Bank of America Corporation or a subsidiary;

•  Any investor participating in an account offered by an intermediary or other entity that provides services to such an account, is paid an asset-based fee by the investor and is not compensated by the Funds for those services, other than payments for shareholder servicing or sub-accounting performed in place of the Fund's transfer agent (each investor purchasing through an intermediary must independently satisfy the minimum investment requirement noted above);

•  Any client of Bank of America Corporation or a subsidiary purchasing through an asset management company, trust, fiduciary, retirement plan administration or similar arrangement with Bank of America Corporation or the subsidiary;

•  Any investor purchasing through a Columbia Management state tuition plan organized under Section 529 of the Internal Revenue Code;

•  Any institutional investor which is a corporation, partnership, trust, foundation, endowment, institution, government entity, or similar organization; which meets the respective qualifications for an accredited investor, as defined under the Securities Act of 1933; or

•  Certain financial institutions and intermediaries, such as insurance companies, trust companies, banks, endowments, investment companies or foundations, purchasing shares for its own account, including Bank of America Corporation, its affiliates, or subsidiaries.

The investment minimum is applied at the class level. For group retirement plans, the investment minimum is determined based on the amount of the plan's investment rather than that of its individual participants. The Fund may establish exclusions from the investment minimum from time to time that it deems appropriate and consistent with the interests of shareholders. Please see the Statement of Additional Information for details on these exclusions.

The Fund reserves the right to change the criteria for eligible investors and the investment minimums. No minimum investment applies to accounts participating in the automatic investment plan; however, each investment requires a $50 minimum purchase. The Fund also reserves the right to refuse a purchase order for any reason, including if it believes that doing so would be in the best interest of the Fund and its shareholders. Finally, pursuant to the Trust's Agreement and Declaration of Trust, the Fund reserves the right to redeem your shares if your account falls below the minimum investment requirements.

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SALES CHARGES (COMMISSIONS)

Your purchases of Class Z shares are at net asset value, which is the value of a Class Z share excluding any sales charge. Class Z shares are not subject to an initial sales charge when purchased, or a contingent deferred sales charge when sold.

CHOOSING A SHARE CLASS

The Fund offers one class of shares in this prospectus — Class Z.

The Fund also offers three additional classes of shares — Class A, B and C shares are available through a separate prospectus. Each other share class has its own sales charge and expense structure.

Broker-dealers, investment advisers or financial planners selling mutual fund shares may offer their clients more than one class of shares in a fund with different pricing options. This allows you and your financial advisor to choose among different types of sales charges and different levels of ongoing operating expenses, depending on the investment programs your financial advisor offers. Investors should consider carefully any separate transactions and other fees charged by these programs in connection with investing in any available share class before selecting a share class.

Determining which share class is best for you depends on the dollar amount you are investing and the number of years for which you are willing to invest. Based on your personal situation, your financial advisor can help you decide which class of shares makes the most sense for you. In general, anyone who is eligible to purchase Class Z shares, which do not incur Rule 12b-1 fees or sales charges, should do so in preference over other classes.

If you purchase Class Z shares of the Fund through certain intermediaries, they may charge a fee for their services. They may also place limits on your ability to use services the Fund offers. There are no sales charges or limitations if you purchase shares directly from the Fund, except as described in this prospectus.

If an intermediary is an agent or designee of the Fund, orders are processed at the net asset value next calculated after the intermediary receives the order. The intermediary must segregate any orders it receives after the close of regular trading on the NYSE and transmit those orders separately for execution at the net asset value next determined.

HOW TO EXCHANGE SHARES

Generally, you may exchange your shares for Class Z or Class A (only if Class Z is not offered) shares of another fund distributed by CMD at net asset value at no additional charge. However, if you exchange shares of Columbia Acorn International Select that you have owned 60 days or less for shares of a fund distributed by CMD that does not have a redemption fee (including Columbia Acorn Fund, Columbia Acorn USA, Columbia Acorn Select and Columbia Thermostat Fund), the Fund will charge you a redemption fee of 2% of the redemption proceeds. Exchanges between Columbia Acorn International and Columbia Acorn International Select (or a fund distributed by CMD that has a redemption fee) will not be subject to the 2% redemption fee. You also may exchange your Class Z shares of any Fund for Class Z shares, or, if there are no Class Z shares, Class A shares of certain other funds distributed by CMD at net asset value without a sales char ge. Unless your account is part of a tax-deferred retirement plan, an exchange is a taxable event, and you may realize a gain or a loss for tax purposes. The Funds may terminate your exchange privilege if the adviser in its discretion determines that your exchange activity may

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adversely impact its ability to manage the Funds. See "Fund Policy on Trading of Fund Shares and Redemption Fees" for the Fund's policy. To exchange by telephone, call 1-800-422-3737. Please have your account and taxpayer identification numbers available when calling.

You also may exchange your shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet exchanges. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

HOW TO SELL SHARES

You may sell shares of the Fund on any regular business day that the NYSE is open.

When the Fund receives your sales request in "good form," shares will be sold at the next calculated price. "Good form" means that the Fund's transfer agent has all information and documentation it deems necessary to effect your order. For example, when selling shares by letter of instruction, "good form" means (i) your letter has complete instructions, the proper signatures and Medallion Signature Guarantees, and (ii) any other required documents are attached. For additional documents required for sales by corporations, agents, fiduciaries, surviving joint owners and other legal entities, please call 1-800-345-6611. Retirement plan accounts have special requirements; please call 1-800-799-7526 for more information.

The Fund will generally send proceeds from the sale to you within seven days (usually on the next business day after your request is received in "good form"). However, if you purchased your shares by check, the Fund may delay sending the proceeds from the sale of your shares for up to 10 days after your purchase to protect against checks that are returned. No interest will be paid on uncashed redemption checks. Redemption proceeds may be paid in securities, rather than cash, under certain circumstances. For more information, see the paragraph "Non-Cash Redemptions" under the section "How to Sell Shares" in the SAI.

During any 90-day period for any one shareholder, the Fund is obligated to redeem shares solely in cash up to the lesser of $250,000 or 1% of the Fund's net assets. Redemptions in excess of these limits will normally be paid in cash, but may be paid wholly or partly by an in-kind distribution of securities.

Outlined below are the various options for selling shares:

Method	Instructions
Through your financial advisor	You may call your financial advisor to place your sell order. To receive the current trading day's price, your financial advisor firm must receive your request prior to the close of regular trading on the NYSE, usually 4:00 p.m. Eastern time. Your financial advisor may charge you fees for executing a redemption for you.
By exchange	You or your financial advisor may sell shares by exchanging from the Fund into Class Z shares or Class A shares (only if Class Z is not offered) of another fund distributed by Columbia Management Distributors, Inc. at no additional cost. To exchange by telephone, call 1-800-422-3737.
By telephone	You or your financial advisor may sell Fund shares by telephone and request that a check be sent to your address of record by calling 1-800-422-3737, unless you have notified the Fund of an address change within the previous 30 days. The dollar limit for telephone sales is $100,000 in a 30-day period. You do not need to set up this feature in advance of your call. Certain restrictions apply to retirement accounts. For details, call 1-800-799-7526.

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Method	Instructions
By mail	You may send a signed letter of instruction to the address below. In your letter of instruction, note the Fund's name, share class, account number, and the dollar value or number of shares you wish to sell. All account owners must sign the letter. Signatures must be guaranteed by either a bank, a member firm of a national stock exchange or another eligible guarantor that participates in the Medallion Signature Guarantee Program for amounts over $100,000 or for alternate payee or mailing instructions. Additional documentation is required for sales by corporations, agents, fiduciaries, surviving joint owners and individual retirement account owners. For details, call 1-800-345-6611. Mail your letter of instruction to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By wire	You may sell Fund shares and request that the proceeds be wired to your bank. You must set up this feature prior to your request. Be sure to complete the appropriate section of the account application for this feature. Generally, the value of your redemption must be at least equal to $500 in order to have the sale proceeds wired to your bank. There is a $7.50 charge for wiring sale proceeds to your bank. (The transfer agent may waive this fee for omnibus and nominee accounts.) Your bank may charge additional fees for such wire transfer.
By systematic withdrawal plan	You may automatically sell a specified dollar amount or percentage of your account on a monthly, quarterly or semiannual basis and have the proceeds sent to you if your account balance is at least $5,000. The $5,000 minimum account balance requirement is waived for wrap accounts. All dividend and capital gains distributions must be reinvested. Be sure to complete the appropriate section of the account application for this feature.
By electronic funds transfer	You may sell Fund shares and request that the proceeds be electronically transferred to your bank. Proceeds may take up to two business days to be received by your bank. You must set up this feature prior to your request. Be sure to complete the appropriate section of the account application for this feature.
Through the internet	You may sell Fund shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet redemptions. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

FUND POLICY ON TRADING OF FUND SHARES AND REDEMPTION FEES

The interests of the Fund's long-term shareholders may be adversely affected by certain short-term trading activity by Fund shareholders. Such short-term trading activity, when excessive, has the potential to interfere with efficient portfolio management, generate transaction and other costs, dilute the value of Fund shares held by long-term shareholders and have other adverse effects on the Fund. This type of excessive short-term trading activity is referred to herein as "market timing." For purposes of this section "Columbia Funds" are the Columbia, Columbia Acorn Trust and Wanger Advisor's Trust families of mutual funds. The Columbia Funds are not intended as vehicles for market timing. The Board of Trustees of the Funds has adopted the policies and procedures set forth below with respect to frequent trading of the Fund's shares.

The Fund, directly and through its agents, takes various steps designed to deter and curtail market timing. For example, if the Fund detects that any shareholder has conducted two "round trips" (as defined below) in the Fund in any 28-day period, except as noted below with respect to orders received through omnibus accounts, the Fund will reject the shareholder's future purchase orders, including exchange purchase orders, involving any Columbia Fund (other than a money market fund). In addition, if the Fund determines that any person, group or account has engaged in any type of market timing activity (independent of the two-round-trip limit), the Fund may, in its discretion, reject future purchase orders by the person, group or account, including exchange purchase orders, involving the same or any other Columbia fund, and also retains the right to modify these market timing policies at any time without prior notice.

The rights of shareholders to redeem shares of the Fund are not affected by any of the limits mentioned above. However, the Fund imposes a redemption fee on the proceeds of Fund shares that are redeemed or exchanged within 60 days of their purchase.

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For these purposes, a "round trip" is a purchase by any means into a Columbia fund followed by a redemption, of any amount, by any means out of the same Columbia fund. Under this definition, an exchange into the Fund followed by an exchange out of the Fund is treated as a single round trip. Also for these purposes, where known, accounts under common ownership or control generally will be counted together. Accounts maintained or managed by a common intermediary, such as an adviser, selling agent or trust department, generally will not be considered to be under common ownership or control.

Purchases, redemptions and exchanges made through the Columbia Funds' Automatic Investment Plan, Systematic Withdrawal Plan or similar automated plans are not subject to the two-round-trip limit. Purchases, redemptions and exchanges made by Columbia Thermostat Fund are also not subject to the two round-trip limit. The two-round-trip limit may be modified for, or may not be applied to, accounts held by certain retirement plans to conform to plan limits, considerations relating to the Employee Retirement Income Security Act of 1974 or regulations of the Department of Labor, and for certain asset allocation or wrap programs.

The practices and policies described above are intended to deter and curtail market timing in the Fund. However, there can be no assurance that these policies, individually or collectively, will be totally effective in this regard because of various factors. In particular, a substantial portion of purchase, redemption and exchange orders are received through omnibus accounts. Omnibus accounts, in which shares are held in the name of an intermediary on behalf of multiple beneficial owners, are a common form of holding shares among financial intermediaries and retirement plans. The Fund typically is not able to identify trading by a particular beneficial owner through an omnibus account, which may make it difficult or impossible to determine if a particular account is engaged in market timing. Consequently, there is the risk that the Fund may not be able to identify, deter or curtail certain market timing that occurs in the Fund, which may result in certain shareholders being able to market time the Fund while the shareholders in the Fund bear the burden of such activities.

Certain financial intermediaries, including certain retirement plan service providers whose clients include, among others, various retirement plans sponsored by Bank of America and its affiliates for the benefit of its employees (the "Bank of America retirement plan service providers"), have different policies regarding monitoring and restricting market timing in the underlying beneficial owner accounts that they maintain through an omnibus account that may be more or less restrictive than the Fund practices discussed above. In particular, the Bank of America retirement plan service providers permit the reinstatement of future purchase orders for shares of the Fund following various suspension periods. If an intermediary does not enforce the Fund's policy, the intermediary must either provide data transparency to Columbia Management or Columbia Management must determine that the intermediary's policy taken in its entirety provid es protections to Fund shareholders that are generally commensurate with the Fund's policy.

The Fund seeks to act in a manner that it believes is consistent with the best interests of Fund shareholders in making any judgments regarding market timing. Neither the Fund nor its agents shall be held liable for any loss resulting from rejected purchase orders or exchanges.

The Fund will assess, subject to limited exceptions, a 2.00% redemption fee on the proceeds of Fund shares that are redeemed (either by selling shares or exchanging into another Columbia fund) within 60 days of their purchase. The redemption fee is paid to the Fund.

The redemption fee is imposed on Fund shares redeemed (including redemptions by exchange) within 60 days of purchase. In determining which shares are being redeemed, the Fund generally applies a first-in, first-out

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approach. For Fund shares acquired by exchange, the holding period prior to the exchange will not be considered in determining whether to assess the redemption fee.

The redemption fee will not be imposed if you qualify for a waiver and the Fund has received proper notification, unless the waiver is automatic as noted below. The Fund redeem any shares that are eligible for a waiver first.

A Fund shareholder won't pay an otherwise applicable redemption fee on any of the following transactions:

•  shares sold following the death or disability (as defined in the tax code) of the shareholder, including a registered joint owner

•  shares sold by or distributions from participant directed retirement plans, such as 401(k), 403(b), 457, Keogh, profit sharing, and money purchase pension accounts, where the Fund does not have access to information about the individual participant account activity, except where the Fund has received an indication that the plan administrator is able to assess the redemption fee to the appropriate accounts (automatic)

•  shares sold by certain investment funds, including those that Columbia Management Advisors, LLC or its affiliates may manage (automatic)

•  shares sold as part of an automatic rebalancing within an asset allocation program or by certain wrap programs where the program sponsor has provided assurances reasonably satisfactory to the Fund that the program is not designed to be a vehicle for market timing

•  shares sold by accounts maintained by a financial institution or intermediary where the Fund has received information reasonably satisfactory to the Fund indicating that the financial institution or intermediary is unable for administrative reasons to assess the redemption fee to underlying shareholders

•  shares sold by an account which has demonstrated a hardship, such as a medical emergency, as determined in the absolute discretion of the Fund

•  shares that were purchased by reinvested dividends (automatic)

•  shares that are redeemed or exchanged through Columbia funds' Systematic Withdrawal Plan or similar affiliated or unaffiliated automated plans

•  the following retirement plan distributions:

•  lump-sum or other distributions from a qualified corporate or self-employed retirement plan following retirement (or following attainment of age 59¹/₂ in the case of a "key employee" of a "top heavy" plan)

•  distributions from an individual retirement account (IRA) or Custodial Account under Section 403(b)(7) of the tax code, following attainment of age 59¹/₂

The Fund also has the discretion to waive the 2.00% redemption fee if the Fund is in jeopardy of failing the 90% income test or losing its registered investment company qualification for tax purposes.

As described above, certain intermediaries do not assess redemption fees to certain categories of redemptions that do not present significant market timing concerns (such as automatic withdrawal plan redemptions). In these situations, the Fund's ability to assess redemption fees is generally limited by the intermediary's policies and, accordingly, no redemption fees will be assessed on such redemptions.

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FINANCIAL INTERMEDIARY PAYMENTS

The Fund's distributor, investment adviser or their affiliates may make payments, from their own resources, to certain financial intermediaries, including other Bank of America affiliates, for marketing support services. For purposes of this section the term "financial intermediary" includes any broker, dealer, bank, bank trust department, registered investment adviser, financial planner, retirement plan or other third-party administrator and any other institution having a selling, services or any similar agreement with the Fund's distributor, investment adviser or one of their affiliates. These payments are generally based upon one or more of the following factors: average net assets of the mutual funds distributed by the Fund's distributor attributable to that financial intermediary, gross sales of the mutual funds distributed by the Fund's distributor attributable to that financial intermediary, reimbursement of ticket charge s (fees that a financial intermediary firm charges its representatives for effecting transactions in fund shares) or a negotiated lump sum payment.

While the financial arrangements may vary for each financial intermediary, the payments to any one financial intermediary are generally expected to be between 0.05% and 0.45% on an annual basis for payments based on average net assets of the Fund attributable to the financial intermediary, and between 0.10% and 0.25% on an annual basis for firms receiving a payment based on gross sales of the Fund attributable to the financial intermediary. The Fund's distributor, investment adviser or their affiliates may make payments in materially larger amounts or on a basis materially different from those described above when dealing with other affiliates of Bank of America. Such increased payments to the other Bank of America affiliate may enable the other Bank of America affiliate to offset credits that it may provide to its customers in order to avoid having such customers pay fees to multiple Bank of America entities in connection with the customer's investment in the Fund.

Payments also may be made to certain financial intermediaries, including other Bank of America affiliates, that provide investor services to retirement plans and other investment programs to compensate financial intermediaries for services they provide to such programs, including, but not limited to, sub-accounting, sub-transfer agency, similar shareholder or participant recordkeeping, shareholder or participant reporting, or shareholder or participant transaction processing. These payments for investor servicing support vary by financial intermediary but generally are not expected, with certain limited exceptions, to exceed 0.45% of the total Fund assets for Class Z shares in the program on an annual basis.

The Trust's Board of Trustees has authorized the Fund to pay to any intermediary up to 0.05% of the average aggregate value of Fund shares in the intermediary's program on an annual basis for providing investor services. Charges of an intermediary in excess of that paid by the Fund will be borne by the Fund's distributor or its affiliates.

The Fund's distributor, investment adviser or their affiliates may make other payments or allow promotional incentives to financial intermediaries to the extent permitted by the rules of the Securities and Exchange Commission, the National Association of Securities Dealers and by other applicable laws and regulations.

Amounts paid by the Fund's distributor, investment adviser or their affiliates are paid out of the distributor's, investment adviser's or their affiliates' own resources and do not increase the amount paid by you or the Fund. You can find further details about the payments made by the Fund's distributor, investment adviser or their affiliates and the services provided by financial intermediaries as well as a list of the financial intermediaries to which the Fund's distributor, investment adviser or their affiliates have agreed to make marketing support payments in the Fund's SAI, which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611. Your financial intermediary may charge you fees or commissions in addition to those disclosed in this prospectus. You can ask y our financial

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intermediary for information about any payments it receives from the Fund's distributor, investment adviser and their affiliates and any services your financial intermediary provides, as well as fees and/or commissions it charges. In addition, depending on the financial arrangement in place at any particular time, a financial intermediary and its financial consultants also may have a financial incentive for recommending a particular fund or share class over others. You should consult with your financial advisor and review carefully any disclosure by the financial intermediary as to compensation received by your financial advisor.

OTHER INFORMATION ABOUT YOUR ACCOUNT

How the Fund's Share Price is Determined The Fund's Class Z share price is based on its net asset value. The net asset value is determined at the close of regular trading on the NYSE, usually 4:00 p.m. Eastern time, on each business day that the NYSE is open for trading (typically Monday through Friday). Net asset value is not determined on days on which the NYSE is closed for trading.

When you request a transaction, it will be processed at the net asset value per share next determined after your request is received in "good form" by the distributor. In most cases, in order to receive that day's price, the Fund must receive your order before that day's transactions are processed. If you request a transaction through your financial advisor, your financial advisor must receive your order by the close of trading on the NYSE to receive that day's price.

The Fund determines its net asset value for its Class Z shares by dividing total net assets attributable to Class Z shares by the number of outstanding Class Z shares. In determining the net asset value, the Fund must determine the value of each security in its portfolio at the close of each trading day. Because the Fund holds securities that are traded on foreign exchanges, the value of the Fund's securities may change on days when shareholders will not be able to buy or sell Fund shares. This will affect the Fund's net asset value on the day it is next determined. Securities for which market quotations are available are valued each day at the current market value. However, where market quotations are unavailable, or when the adviser believes that subsequent events have made them unreliable, the Fund may use other data to determine the fair value of the securities.

The Fund has retained an independent statistical fair value pricing service to assist in the fair valuation process for securities principally traded in a foreign market in order to adjust for possible changes in value that may occur between the close of the foreign exchange and the time at which Fund shares are priced. The use of an independent fair value pricing service is intended to and may decrease the opportunities for time zone arbitrage transactions. There can be no assurance that the use of an independent fair value pricing service will successfully decrease arbitrage opportunities. If a security is valued at a "fair value," that value may be different from the last quoted market price for the security.

You can find the daily prices of some share classes for the Fund in most major daily newspapers under the heading of "Columbia." You can find daily prices for all share classes by visiting www.columbiafunds.com.

Share Certificates Share certificates are not available for Class Z shares.

Dividends, Distributions, and Taxes The Fund has the potential to make the following distributions:

Types of Distributions

Dividends	Represents interest and dividends earned from securities held by the Fund, net of expenses incurred by the Fund.
Capital gains	Represents net long-term capital gains on sales of securities held for more than one year and net short-term capital gains, which are gains on sales of securities held for a one-year period or less.

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Distribution Options The Fund distributes any dividends in June and December and any capital gains (including short-term capital gains) at least annually. You can choose one of the options listed in the table below for these distributions when you open your account. To change your distribution option call 1-800-345-6611.

If you do not indicate on your application or at the time your account is established your preference for handling distributions, the Fund will automatically reinvest all distributions in additional shares of the Fund.

UNDERSTANDING FUND DISTRIBUTIONS

The Fund may earn income from the securities it holds. The Fund also may realize capital gains or losses on sales of its securities. The Fund intends to distribute substantially all of its net investment income and capital gains to shareholders each year. As a shareholder, you are entitled to a portion of the Fund's income and capital gains based on the number of shares you own at the time these distributions are declared.

Distribution Options

Reinvest all distributions in additional shares of the fund

Reinvest all distributions in shares of another fund

Receive dividends in cash (see options below) and reinvest capital gains

Receive all distributions in cash (with one of the following options):

•  send the check to your address of record

•  send the check to a third-party address

•  transfer the money to your bank via electronic funds transfer

Distributions of $10 or less will automatically be reinvested in additional Fund shares. If you elect to receive distributions by check and the check is returned as undeliverable, all subsequent distributions will be reinvested in additional shares of the Fund.

Taxes Unless you are an entity exempt from income taxes or invest under a retirement account, regardless of whether you receive your distributions in cash or reinvest them in additional Fund shares, all Fund distributions are subject to federal income tax. Depending on where you live, distributions also may be subject to state and local income taxes.

The Fund intends to elect to be treated and to qualify each year as a regulated investment company. A regulated investment company is not subject to tax at the corporate level on income and gains from investments that are distributed to shareholders in accordance with applicable law. However, the Fund's failure to qualify as a regulated investment company could result in corporate level taxation, and consequently, a reduction in income available for distribution to shareholders.

In general, any distributions of dividends, interest and short-term capital gains (determined by how long the Fund held the investments that generated them) are taxable as ordinary income, unless such dividends are "qualified dividend income" (as defined in the Internal Revenue Code) eligible for a reduced rate of tax. Properly designated distributions of long-term capital gains (determined by how long the Fund held the investments that generated them) are generally taxable as such, regardless of how long you have held your Fund shares. You will be provided with information each year regarding the amount of ordinary income and capital gains distributed to you for the previous year and any portion of your distribution which is exempt from state and local taxes. Long-term

18

Your Account

capital gain rates have been reduced — in general, to 15% with lower rates applying to taxpayers in the 10% and 15% rate brackets — for taxable years beginning before January 1, 2011. Distributions are taxable to you even if they are paid from income or gains earned by the Fund before you made your investment (and thus were included in the price you paid). Your investment in the Fund may have additional personal tax implications. Please consult your tax advisor about foreign, federal, state, local or other applicable tax laws.

In addition to the dividends and capital gains distributions made by the Fund, you may realize a capital gain or loss when selling or exchanging shares of the Fund. Such transactions also may be subject to federal, state and local income tax.

Foreign Income Taxes The Fund may receive investment income from sources within foreign countries, and that income may be subject to foreign income taxes at the source. If the Fund pays non-refundable taxes to foreign governments during the year, the taxes will reduce the Fund's dividends but will still be included in your taxable income. You may be able to claim a credit or deduction on your tax return for your share of foreign taxes paid by the Fund.

Board of Trustees

The Fund is governed by its Board of Trustees. More than 75% of the Fund's Trustees are independent, meaning that they have no affiliation with the adviser or the Funds, apart from their positions as Trustees and the personal investments they may have made as private individuals.

The independent Trustees bring backgrounds in business and the professions and academia to their task of working with the Funds' officers to establish the policies and oversee the activities of the Funds. Among the Trustees' responsibilities are selecting the investment adviser for the Funds; negotiating the advisory agreements; reviewing other contracts; approving investment policies; monitoring Fund operations, performance, and costs; and nominating or selecting new Trustees.

Each Trustee serves until his or her retirement, resignation, death or removal; or otherwise as specified in the Trust's organizational documents. It is expected that every five years the Trustees will call a meeting of shareholders to elect Trustees. A Trustee must retire at the end of the year in which he or she attains the age of 75. Any Trustee may be removed at a shareholders' meeting by a vote representing two-thirds of the net asset value of all shares of the Funds of the Trust. The mailing address for the Trustees and officers is 227 W. Monroe, Suite 3000, Chicago, Illinois 60606.

For more detailed information on the Board of Trustees, please refer to the SAI.

19

Managing the Fund

INVESTMENT ADVISER

Columbia Wanger Asset Management, L.P. (CWAM), located at 227 West Monroe Street, Suite 3000, Chicago, Illinois 60606, is the Fund's investment adviser and is responsible for the Fund's management, subject to the oversight of the Fund's Board of Trustees. CWAM and its predecessor have managed mutual funds, including the Fund, since 1992. In its duties as investment adviser, CWAM runs the Fund's day-to-day business, including making investment decisions and placing all orders for the purchase and sale of the Fund's portfolio securities.

CWAM was previously named Liberty Wanger Asset Management, L.P. and its predecessor was named Wanger Asset Management, L.P. (WAM). CWAM is a wholly owned subsidiary of Columbia Management Group, LLC, which is an indirect wholly owned subsidiary of Bank of America Corporation. As of December 31, 2006, CWAM managed more than $32.9 billion in assets.

CWAM's advisory fee for managing the Fund in 2006 was 0.94% of the Fund's average daily net assets. CWAM also received an administrative fee from the Fund in 2006 of 0.04% of the Fund's average daily net assets. A discussion of the factors considered by the Fund's Board of Trustees in approving the Fund's investment advisory contract is included in the Fund's annual report to shareholders for the period ended December 31, 2006.

PORTFOLIO MANAGER

CWAM uses a team to assist the lead portfolio manager in managing the Fund. Team members share responsibility for providing ideas, information and knowledge in managing the Fund, and each team member has one or more particular areas of expertise. The portfolio manager is responsible for making daily investment decisions and utilizing the management team's input and advice when making buy and sell determinations.

Christopher J. OlsonLead portfolio manager
Christopher J. Olson is a vice president of the Trust and has managed Columbia Acorn International Select since September 2001. He has been a member of the international analytical team at CWAM since January 2001. Mr. Olson also is a vice president of Wanger Advisors Trust, a co-portfolio manager of Wanger International Small Cap and the lead portfolio manager of Wanger International Select, two international mutual funds underlying variable insurance products.

The Statement of Additional Information provides additional information about the portfolio manager's compensation, other accounts managed and ownership of securities in the Fund.

LEGAL PROCEEDINGS

The Trust, CWAM and the trustees of the Trust (collectively the "Columbia defendants") are named as defendants in class and derivative complaints, which were consolidated in a Multi-District Action in the federal district court for the District of Maryland on February 20, 2004 (the "MDL Action"). These lawsuits contend that defendants permitted certain investors to market time their trades in certain Columbia Acorn Funds. All MDL Action is ongoing. All claims against the Trust and its independent trustees have been dismissed; however, the interested trustees of the Trust are still parties to the MDL Action.

On March 21, 2005, a class action complaint was filed against the Trust in the Superior Court of the Commonwealth of Massachusetts seeking to rescind the contingent deferred sales charges assessed upon redemption of Class B shares of Columbia Acorn Funds due to the alleged market timing of the Columbia Acorn

20

Managing the Fund

Funds. In addition to the rescission of sales charges, plaintiffs seek recovery of actual damages, attorneys' fees and costs. The case has been transferred to the MDL Action in the federal district court of Maryland.

The Trust and CWAM are also defendants in a class action lawsuit, filed on November 13, 2003 in the Circuit Court of the Third Judicial Circuit, Madison County, Illinois, that alleges, in summary, that the Trust and CWAM exposed shareholders of Columbia Acorn International to trading by market timers by allegedly (a) failing to properly evaluate daily whether a significant event affecting the value of that fund's securities had occurred after foreign markets had closed but before the calculation of the fund's net asset value; (b) failing to implement the fund's portfolio valuation and share pricing policies and procedures; and (c) failing to know and implement applicable rules and regulations concerning the calculation of net asset value ("Fair Valuation Lawsuit"). On April 5, 2005, the United States Court of Appeals for the Seventh Circuit ruled that the plaintiffs' state law claims were preempted under federal law resulting in the dismissal of plaintiffs' complaint. Plaintiffs appealed the Seventh Circuit's ruling to the United States Supreme Court. On June 15, 2006, the Supreme Court reversed the Seventh Circuit's ruling on jurisdictional grounds, and the case ultimately was remanded to the state court.

On April 4, 2006, the plaintiffs and the Columbia defendants named in the MDL Action executed an agreement in principle intended to fully resolve all of the lawsuits consolidated in the MDL Action as well as the Fair Valuation Lawsuit. The court entered a stay after the parties executed the agreement in principle. The settlement is subject to court approval.

In 2004, CWAM and the trustees of the Columbia Acorn Trust were named as defendants in certain purported shareholder class and derivative actions making claims, including claims under the Investment Company and the Investment Advisers Acts of 1940 and state law. Certain Columbia Acorn Funds were named as nominal defendants. The suits allege, inter alia, that the fees and expenses paid by the funds are excessive and that the funds' advisers and their affiliates inappropriately used fund assets to distribute the funds and for other improper purposes. On March 2, 2005, the actions were consolidated in the Massachusetts federal court as In re Columbia Entities Litigation. The plaintiffs filed a consolidated amended complaint on June 9, 2005. On November 30, 2005, the judge dismissed all claims by plaintiffs and entered final judgment in favor of the defendants. The plaintiffs appealed to the United States Court of Appeals for the First Circuit on December 30, 2005. A stipulation and settlement agreement dated January 19, 2007 was filed in the First Circuit on February 14, 2007, with a joint stipulation of dismissal and motion for remand to obtain district court approval of the settlement. The joint motion was granted and the appeal was dismissed. On March 6, 2007, the case was remanded to the District Court, where the parties will seek court approval of the settlement. The terms of the proposed settlement, if approved, will require payments by the funds' adviser and/or its affiliates, including payment of plaintiffs' attorneys' fees and notice to class members. In the event that the settlement is not approved, the plaintiffs may elect to g o forward with their appeal and no opinion is expressed regarding the likely outcome or financial impact of such an appeal on any fund.

On or about January 11, 2005, a putative class action lawsuit was filed in federal district court in Massachusetts against the Trust and its trustees, along with Columbia Management Advisors, LLC, the sub-administrator of the Wanger Advisors Funds and the Columbia Acorn Funds. The plaintiffs allege that the defendants failed to submit Proof of Claims in connection with settlements of securities class action lawsuits filed against companies in which the Columbia Acorn Funds held positions. The complaint seeks compensatory and punitive damages, and the disgorgement of all fees paid to Columbia Management Advisors, LLC. Plaintiffs have voluntarily dismissed the Trust and its independent trustees.

21

Managing the Fund

The Trust and CWAM intend to defend these suits vigorously.

As a result of these matters or any adverse publicity or other developments resulting from them, there may be increased redemptions or reduced sales of Fund shares, which could increase transaction costs or operating expenses, or have other adverse consequences for the Fund.

However, based on currently available information, the Trust believes that the likelihood that these lawsuits will have a material adverse impact on any fund is remote, and CWAM believes that the lawsuits are not likely to materially affect its ability to provide investment management services to the Fund.

22

Other Investment Strategies and Risks

The Fund's principal investment strategies and associated risks are described under "The Fund — Principal Investment Strategies" and "The Fund — Principal Investment Risks." This section describes other investments the Fund may make and the risks associated with them. In seeking to achieve its investment goal, the Fund may invest in various types of securities and engage in various investment techniques, which are not the principal focus of the Fund and therefore are not described in this prospectus. These types of securities and investment practices and their associated risks are identified and discussed in the Fund's SAI, which you may obtain free of charge (see back cover). The adviser may elect not to buy any of these securities or use any of these techniques. The Fund may not always achieve its investment goal. Except as otherwise noted, approval by the Fund's shareholders is not required to modify or change the F und's investment strategies.

THE INFORMATION EDGE

The Fund generally invests in entrepreneurially managed smaller- and mid-sized companies that it believes are not as well known by financial analysts and whose position in a niche creates the opportunity for superior earnings-growth potential. CWAM may identify what it believes are important economic, social or technological trends (for example, the growth of outsourcing as a business strategy, or the productivity gains from the increasing use of technology) and try to identify companies it thinks will benefit from those trends.

In making investments for the Fund, CWAM relies primarily on independent, internally generated research to uncover companies that may be less well known than the more popular names. To find these companies, CWAM compares growth potential, financial strength and fundamental value among companies.

Growth Potential	Financial Strength	Fundamental Value
• superior technology • innovative marketing • managerial skill • market niche • good earnings prospects • strong demand for product	• low debt • adequate working capital • conservative accounting practices • adequate profit margin	• reasonable stock price relative to growth potential and financial strength • valuable assets
The realization of this growth potential would likely produce superior performance that is sustainable over time.	A strong balance sheet gives management greater flexibility to pursue strategic objectives and is important to maintaining a competitive advantage.	Once CWAM uncovers an attractive company, it identifies a price that it believes would also make the stock a good value.

LONG-TERM INVESTING

CWAM's analysts continually screen companies and make contact with more than 1,000 companies around the globe each year. To accomplish this, CWAM analysts often talk directly to top management, vendors, suppliers and competitors.

In managing the Fund, CWAM tries to maintain lower taxes and transaction costs by investing with a long-term time horizon (at least two to five years). However, securities purchased on a long-term basis may be sold within 12 months after purchase due to changes in the circumstances of a particular company or industry, or changes in general market or economic conditions.

23

Other Investment Strategies and Risks

DERIVATIVE STRATEGIES

The Fund may enter into a number of derivative strategies, including those that employ futures, options, straddles or similar transactions, to gain or reduce exposure to particular securities or markets. These strategies, commonly referred to as derivatives, involve the use of financial instruments whose values depend on, or are derived from, the value of an underlying security, index or currency. The Fund may use these strategies to adjust the Fund's sensitivity to changes in interest rates, or for other hedging purposes (i.e., attempting to offset a potential loss in one position by establishing an interest in an opposite position). Derivative strategies involve the risk that they may exaggerate a loss, potentially losing more money than the actual cost of the underlying security, or limit a potential gain. Also, with some derivative strategies there is a risk that the other party to the transaction may fail to honor its contr act terms, causing a loss to the Fund or that the Fund may not be able to find a suitable derivative transaction counterparty, and thus may be unable to invest in derivatives altogether.

TEMPORARY DEFENSIVE STRATEGIES

At times, CWAM may determine that adverse market conditions make it desirable to temporarily suspend the Fund's normal investment activities. During such times, the Fund may, but is not required to, invest in cash or high-quality, short-term debt securities, without limit. Taking a temporary defensive position may prevent the Fund from achieving its investment goal.

24

Financial Highlights

The financial highlights table is intended to help you understand the Fund's Class Z financial performance. Information is shown for the Fund's last five fiscal years, which run from January 1 to December 31. Certain information in the table reflects the financial results for a single Class Z share. The total returns in the table represent the return that you would have earned (or lost) on an investment in the Fund (assuming reinvestment of all dividends and distributions). This information has been derived from the Fund's financial statements, which have been audited by for the years ended December 31, 2004, 2005 and 2006 by PricewaterhouseCoopers LLP, an independent registered public accounting firm, whose report, along with the Fund's financial statements, is included in the Fund's annual report. The information for the years ended December 31, 2002 and 2003 is included in the Fund's financial statements that have been audite d by another independent registered public accounting firm, whose report expressed an unqualified opinion on those financial statements and highlights. You can request a free annual report containing those financial statements by calling 1-800-345-6611.

Columbia Acorn International Select

	Year ended December 31,
	2006			2005			2004			2003			2002
	Class Z			Class Z			Class Z			Class Z			Class Z
Net asset value — beginning of period ($)		20.57			18.02			14.58			10.29			12.09
Income from Investment Operations ($)
Net investment income(a)		0.10			0.13			0.04			0.06			0.03
Net realized and unrealized gain (loss)		7.35			2.70			3.47			4.24			(1.83	)
Total from Investment Operations		7.45			2.83			3.51			4.30			(1.80	)
Less Distributions Declared to Shareholders ($):
From net investment income		(0.05	)		(0.28	)		(0.07	)		(0.01	)		—
Total Distributions Declared to Shareholders		(0.05	)		(0.28	)		(0.07	)		(0.01	)		—
Redemption Fees
Redemption fees added to paid in capital		0.00	(a)(b)		0.00	(a)(b)		0.00	(a)(b)		—			—
Net asset value — end of period ($)		27.97			20.57			18.02			14.58			10.29
Total return (%)(c)(d)		36.27			15.98			24.14			41.79			(14.89	)
Ratios to Average Net Assets/Supplemental Data (%):
Expenses(e)		1.27			1.45			1.45			1.45			1.45
Net investment income(e)		0.44			0.72			0.27			0.56			0.26
Waiver/reimbursement		0.01			0.04			0.29			0.42			0.33
Portfolio turnover rate (%)		47			39			73			69			102
Net assets at end of period (in millions) ($)		129			74			46			34			26

(a)  Per share data was calculated using average shares outstanding during the period.

(b)  Rounds to less than $0.01 per share.

(c)  Total return at net asset value assuming all distributions reinvested.

(d)  Had the investment adviser and/or transfer agent not waived and/or reimbursed a portion of expenses, total return would have been reduced.

(e)  The benefits derived from custody fees paid indirectly had no impact.

25

Appendix

Hypothetical Investment and Expense Information

The Fund is required to disclose the following supplemental hypothetical investment information, which provides additional information about the effect of the expenses paid by the Fund, including investment advisory fees and other Fund costs, on the Fund's returns over a 10-year period. The table shows the estimated expenses that would be charged on a hypothetical investment of $10,000 in Class Z shares of the Fund assuming a 5% return each year, the cumulative return after fees and expenses, and the hypothetical year-end balance after fees and expenses. The table also assumes that all dividends and distributions are reinvested. The annual expense ratio used for the Fund, which is the same as that stated in the Annual Fund Operating Expenses table, is presented in the table, and is net of any contractual fee waivers or expense reimbursements for the period of the contractual commitment. Your actual costs may be higher or lower.< /font>

Columbia Acorn International Select — Class Z Shares

Maximum Sales Charge 0.00%					Initial Hypothetical Investment Amount $10,000.00						Assumed Rate of Return 5%
Year		Cumulative Return Before Fees & Expenses			Annual Expense Ratio			Cumulative Return After Fees & Expenses			Hypothetical Year-End Balance After Fees & Expenses		Annual Fees & Expenses(1)
	1		5.00	%		1.28	%		3.72	%	$	10,372.00	$	130.38
	2		10.25	%		1.28	%		7.58	%	$	10,757.84	$	135.23
	3		15.76	%		1.28	%		11.58	%	$	11,158.03	$	140.26
	4		21.55	%		1.28	%		15.73	%	$	11,573.11	$	145.48
	5		27.63	%		1.28	%		20.04	%	$	12,003.63	$	150.89
	6		34.01	%		1.28	%		24.50	%	$	12,450.16	$	156.50
	7		40.71	%		1.28	%		29.13	%	$	12,913.31	$	162.33
	8		47.75	%		1.28	%		33.94	%	$	13,393.68	$	168.36
	9		55.13	%		1.28	%		38.92	%	$	13,891.93	$	174.63
	10		62.89	%		1.28	%		44.09	%	$	14,408.71	$	181.12
Total Gain After Fees and Expenses											$	4,408.71
Total Annual Fees and Expenses													$	1,545.18

(1)  Annual Fees and Expenses are calculated based on the average between the beginning and ending balance for each year. All information is calculated on an annual compounding basis.

26

Notes

27

FOR MORE INFORMATION

Additional information about the Fund's investments is available in the Fund's semiannual and annual reports to shareholders. The annual report contains a discussion of the market conditions and investment strategies that significantly affected the Fund's performance during its last fiscal year.

You may wish to read the SAI for more information on the Fund and the securities in which it invests. The SAI is incorporated into this prospectus by reference, which means that it is considered to be part of this prospectus.

You can get free copies of annual and semiannual reports and the SAI, request other information and discuss your questions about the Fund by visiting www.columbiafunds.com or by writing or calling the Fund's transfer agent at:

Columbia Management Services, Inc.
P.O. Box 8081
Boston, MA 02266-8081
1-800-345-6611

Text-only versions of all Fund documents can be viewed online or downloaded from the EDGAR database on the Securities and Exchange Commission internet site at www.sec.gov.

You can review and copy information about the Fund, including the SAI, by visiting the following location, and you can obtain copies upon payment of a duplicating fee, by electronic request at the e-mail address publicinfo@sec.gov or by writing the:

Public Reference Room
Securities and Exchange Commission
Washington, DC 20549-0102

Information on the operation of the Public Reference Room may be obtained by calling 1-202-942-8090.

Investment Company Act file number:
Columbia Acorn Trust: 811-01829
•  Columbia Acorn International Select

©2007 Columbia Management Distributors, Inc.
One Financial Center, Boston, MA 02111-2621
800.426.3750 www.columbiafunds.com

INT-36/130114-0507

Columbia^SM

Acorn Select^SM  Prospectus, May 1, 2007

Class A, B and C Shares

Advised by Columbia Wanger Asset Management, L.P.

TABLE OF CONTENTS

THE FUND	2
Investment Goal	2
Principal Investment Strategies	2
Principal Investment Risks	2
Portfolio Holdings Disclosure	3
Performance History	4
Commissions and Other Expenses	5
YOUR ACCOUNT	7
Choosing a Share Class	7
How to Buy Shares	8
Investment Minimums	8
Sales Charges (Commissions)	9
How to Exchange Shares	15
How to Sell Shares	15
Fund Policy on Trading of Fund Shares	17
Other Information About Your Account	18
BOARD OF TRUSTEES	20
MANAGING THE FUND	21
Investment Adviser	21
Portfolio Manager	21
Legal Proceedings	21
OTHER INVESTMENT STRATEGIES AND RISKS	23
The Information Edge	23
Long-Term Investing	23
Derivative Strategies	24
Temporary Defensive Strategies	24
FINANCIAL HIGHLIGHTS	25
APPENDIX	28

Although these securities have been registered with the Securities and Exchange Commission, the Commission has not approved or disapproved any shares offered in this prospectus or determined whether this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Acorn Select is a trademark owned and registered by Columbia Acorn Trust, Columbia, Columbia Management^® and Columbia Management Services, Inc. are service marks owned and/or registered by Bank of America

The Fund

INVESTMENT GOAL

Columbia Acorn Select (Acorn Select^SM) seeks long-term growth of capital.

PRINCIPAL INVESTMENT STRATEGIES

Acorn Select invests generally in the stocks of U.S. companies. The Fund is a non-diversified fund that takes advantage of its adviser's research and stock-picking capabilities to invest in a limited number of companies (between 20-40) with market capitalizations under $20 billion at the time of initial purchase, offering the potential to provide above-average growth over time.

Acorn Select believes that companies within this capitalization range, which are not as well known by financial analysts as the largest companies, may offer higher return potential than the stocks of companies with capitalizations above $20 billion.

Acorn Select typically looks for companies with:

•  A strong business franchise that offers growth potential.

•  Products and services that give the company a competitive advantage.

•  A stock price the Fund's investment adviser believes is reasonable relative to the assets and earning power of the company.

Although Acorn Select does not buy securities with a short-term view, there is no restriction on the length of time the Fund must hold a security. To the extent the Fund buys and sells securities frequently, its transaction costs will be higher (which may adversely affect the Fund's performance) and it may realize additional capital gains.

Acorn Select invests the majority of its assets in U.S. companies, but also may invest up to 25% of its assets, valued at the time of investment, in companies outside the United States in developed markets (for example, Japan, Canada and the United Kingdom) and emerging markets (for example, Mexico, Brazil and Korea).

Additional strategies that are not principal investment strategies and the risks associated with them are described later in this prospectus under "Other Investment Strategies and Risks."

PRINCIPAL INVESTMENT RISKS

The principal risks of investing in the Fund are described below. There are many circumstances (including additional risks that are not described here) which could prevent the Fund from achieving its investment goal. You may lose money by investing in the Fund.

Management risk means that the adviser's investment decisions might produce losses or cause the Fund to underperform when compared to other funds with a similar investment goal. Market risk means that security prices in a market, sector or industry may fall, reducing the value of your investment. Because of management and market risk, there is no guarantee that the Fund will achieve its investment goal or perform favorably among comparable funds.

Since the Fund purchases equity securities, it is subject to equity risk. This is the risk that stock prices will fall over short or extended periods of time. Although the stock market historically has outperformed other asset classes over the long term, the stock market tends to move in cycles. Individual stock prices may fluctuate drastically from day-to-day and may underperform other asset classes over an extended period of time. Individual companies may report poor results or be negatively affected by industry and/or economic trends and developments. The prices of securities issued by such companies may suffer a decline in response. These price movements may result from factors affecting individual companies, industries or the securities market as a whole.

2

The Fund

Because the Fund invests in stocks, the price of its shares — its net asset value (NAV) per share — fluctuates daily in response to changes in the market value of stocks.

Sector risk is inherent in the Fund's investment strategy. Companies that are in different but closely related industries are sometimes described as being in the same broad economic sector. The values of stocks of different companies in a market sector may be similarly affected by particular economic or market events. Although the Fund does not intend to focus on any particular sector, at times the Fund may have a large portion of its assets invested in a particular sector.

Small- or mid-cap companies may be more susceptible to market downturns, and their prices could be more volatile than large-cap companies. These companies are more likely than larger companies to have limited product lines, operating histories, markets or financial resources. They may depend heavily on a small management team and may trade less frequently, may trade in smaller volumes and may fluctuate more sharply in price than stocks of larger companies. In addition, such companies may not be widely followed by the investment community, which can lower the demand for their stocks.

Foreign securities are subject to special risks. Foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the dollar value of foreign securities denominated in foreign currencies and U.S. dollars, without a change in the intrinsic value of those securities. The liquidity of foreign securities may be more limited than that of domestic securities, which means that the Fund may, at times, be unable to sell foreign securities at desirable prices. Brokerage commissions, custodial fees and other fees are generally higher for foreign investments. In addition, foreign governments may impose withholding taxes that would reduce the amount of income and capital gains available to distribute to shareholders. Other risks include possible delays in the settlement of transactions or in the notification of income; less publicly av ailable information about companies; the impact of political, social or diplomatic events; possible seizure, expropriation or nationalization of the company or its assets; and possible imposition of currency exchange controls.

Investments in emerging markets are subject to additional risk. The risks of foreign investments are typically increased in less developed countries, which are sometimes referred to as emerging markets. For example, political and economic structures in these countries may be new and developing rapidly, which may cause instability. These countries are also more likely to experience high levels of inflation, deflation or currency devaluations, which could hurt their economies and securities markets.

As a non-diversified mutual fund, the Fund is allowed to invest a greater percentage of its total assets in the securities of fewer issuers than a "diversified" fund. The Fund may, therefore, have a greater risk of loss from a few issuers than a similar fund that invests more broadly.

An investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PORTFOLIO HOLDINGS DISCLOSURE

A description of the Fund's policies and procedures with respect to the disclosure of its portfolio securities is available in the Fund's Statement of Additional Information (SAI), which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611.

The Fund posts its complete portfolio holdings as of month-end at www.columbiafunds.com approximately 30-40 calendar days after such month-end. Additionally, the Fund discloses its top 15 month-end portfolio holdings at www.columbiafunds.com on or about 15 calendar days following such month-end.

Once posted, the above information will remain available on the website until at least the date on which the Fund files a Form N-CSR or Form N-Q for the period that includes the date as of which the information is current.

3

The Fund

PERFORMANCE HISTORY

The bar chart below shows the Fund's calendar-year total returns (before taxes) for its Class A shares, excluding sales charges. The performance table following the bar chart shows how the Fund's average annual total returns for Class A, B and C shares, including sales charges, compare with a broad measure of market performance for one year, five years and the life of the share class. The chart and table are intended to illustrate some of the risks of investing in the Fund by showing changes in the Fund's performance from year to year. As with all mutual funds, past performance (before and after taxes) does not predict the Fund's future performance.

UNDERSTANDING PERFORMANCE

Calendar Year Total Returns show the Fund's Class A share performance for each completed calendar year since the Class commenced operations. Those returns include the effects of Fund expenses, but not the effects of sales charges paid directly by a shareholder. If sales charges were included, these returns would be lower.

Average Annual Total Returns are a measure of the Fund's average performance over the past one year, five years and the life of the share class. The table shows returns of each share class and includes the effects of both Fund expenses and current sales charges. Class B share returns do not reflect Class A share returns after conversion of Class B shares to Class A shares — see the section "Your Account — Sales Charges (Commissions)."

The Fund's returns are compared to the Standard & Poor's MidCap 400 Index (S&P MidCap 400 Index). The S&P MidCap 400 Index is an unmanaged, market value-weighted index of 400 mid-cap U.S. companies. Unlike the Fund, an index is not an investment, does not incur fees, expenses or taxes, and is not professionally managed.

Calendar Year Total Returns (Class A)

For the periods shown in bar chart:
Best quarter: 4th quarter 2001, +17.47%
Worst quarter: 3rd quarter 2001, -11.43%

After-tax returns are calculated using the highest historical individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on each investor's own tax situation and may differ from those shown. After-tax returns may not be relevant to investors who hold Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

4

The Fund

Average Annual Total Returns — for periods ended December 31, 2006⁽¹⁾

Share Class	1 Year		5 Years		Life of the Share Class(2)
Class A (%)
Return Before Taxes		12.46		11.93		11.89
Return After Taxes on Distributions		11.96		11.64		11.60
Return After Taxes on Distributions and Sale of Fund Shares		8.50		10.37		10.40
Class B (%)
Return Before Taxes		13.54		12.24		12.20
Return After Taxes on Distributions		13.03		11.96		11.92
Return After Taxes on Distributions and Sale of Fund Shares		9.25		10.66		10.68
Class C (%)
Return Before Taxes		17.37		12.44		12.16
Return After Taxes on Distributions		16.86		12.16		11.88
Return After Taxes on Distributions and Sale of Fund Shares		11.74		10.84		10.65
Index
S&P MidCap 400 Index (%)		10.32		10.89		9.14	(3)

(1)  Performance may reflect any voluntary waiver or reimbursement of Fund expenses by the investment adviser or its affiliates. Absent these waivers or reimbursement arrangements, performance results would have been lower.

(2)  The inception date for Class A, Class B and Class C shares is October 16, 2000.

(3)  Performance information is from October 16, 2000.

COMMISSIONS AND OTHER EXPENSES

Expenses are one of several factors to consider before you invest in a mutual fund. The tables below describe the commissions and other expenses you may pay when you buy, hold and sell shares of the Fund.

UNDERSTANDING EXPENSES

Sales Charges (Commissions) are paid directly by shareholders to Columbia Management Distributors, Inc., the Fund's distributor, who compensates your financial advisor.

Annual Fund Operating Expenses are paid by the Fund. They include management and administration fees, 12b-1 fees and other expenses that generally include, but are not limited to, transfer agency, custody, and legal fees as well as costs related to state registration and printing of Fund documents. The specific fees and expenses that make up the Fund's other expenses will vary from time to time and may include fees or expenses not described here. The Fund will likely incur portfolio transaction costs that are in addition to the total annual fund operating expenses disclosed in the fee table. These transaction costs are made up of all costs that are associated with trading securities for the Fund's portfolio and include, but are not limited to, brokerage commissions and market spreads, as well as potential changes to the price of a security due to the Fund's efforts to purchase or sell it. While certain elements of transaction costs are readily identifiable and quantifiable, other elements that can make up a significant amount of the Fund's transaction costs are not. Higher transaction costs reduce the Fund's returns.

5

The Fund

Shareholder Fees (commissions paid directly from your investment)

	Class A			Class B		Class C
Maximum sales charge (load) on purchases (%) (as a percentage of the offering price)		5.75		None		None
Maximum deferred sales charge (load) on redemptions (%) (as a percentage of the lesser of purchase price or redemption price)		1.00	(1)		5.00		1.00
Redemption fee (%) (as a percentage of amount redeemed, if applicable)	None(2)			None(2)		None(2)

(1)  This charge applies only to certain purchases of Class A shares bought without an initial sales charge that are sold within 12 months of purchase.

(2)  There is a $7.50 charge for wiring sale proceeds to your bank.

Annual Fund Operating Expenses (deducted directly from Fund assets)

	Class A		Class B		Class C
Management fees(1) (%)		0.82		0.82		0.82
Distribution and service (12b-1) fees(2) (%)		0.25		0.75		1.00
Other expenses(3) (%)		0.20		0.31		0.26
Total annual fund operating expenses(4) (%)		1.27		1.88		2.08

(1)  The Fund pays an investment advisory fee of 0.82%. The Fund's adviser has implemented a breakpoint schedule for the Fund's investment advisory fees. The investment advisory fees charged to the Fund will decline as Fund assets grow and will continue to be based on a percentage of the Fund's average daily assets. The breakpoint schedule for the Fund is as follows: 0.85% for assets up to $700 million; 0.80% for assets in excess of $700 million and up to $2 billion; 0.75% for assets in excess of $2 billion and up to $3 billion; and 0.70% for assets in excess of $3 billion. In addition to the management fee, the Fund and the other funds of Columbia Acorn Trust (the "Trust") pay the adviser an administrative fee based on the average daily aggregate net assets of the Trust at the following annual rates: 0.05% of net assets up to $8 billion; 0.04% of the next $8billion; and 0.03% of net assets in excess of $16 billion. Based on the Trust's average daily net assets as of December 31, 2006, the administrative fee would be at a rate of 0.04% and is included in "Other expenses."

(2)  The distribution and service (12b-1) fees for Class B shares have been restated to reflect a reduction of the distribution fee rate by 0.10%, effective August 1, 2006.

(3)  "Other expenses" have been restated to reflect contractual changes to the transfer agency fees paid by the Fund.

(4)  The Fund's adviser has voluntarily agreed to reimburse the Fund for any ordinary operating expenses (exclusive of distribution and service fees, interest, taxes and extraordinary expenses, if any) exceeding the annual rate of 1.35% of the average daily net assets for Class A, Class B & Class C shares. This arrangement may be modified or terminated by either the Fund or its adviser on 30 days notice.

Example Expenses help you compare the cost of investing in the Fund to the cost of investing in other mutual funds. The table does not take into account the contractual expense waiver and any other expense reduction arrangements discussed in the footnotes to the Annual Fund Operating Expenses table. It uses the following hypothetical conditions:

•  $10,000 initial investment^†

•  5% total return for each year

•  Fund operating expenses remain the same

•  Reinvestment of all dividends and distributions

•  Class B shares convert to Class A shares after eight years

†  For example only, since the minimum initial investment in the Fund is $50,000.

6

The Fund

Example Expenses for a $10,000 investment (your actual costs may be higher or lower)

Class		1 Year		3 Years		5 Years		10 Years
Class A:		$	697	$	955	$	1,232	$	2,021
Class B:	did not sell your shares	$	191	$	591	$	1,016	$	2,042
	sold all your shares at the end of the period	$	691	$	891	$	1,216	$	2,042
Class C:	did not sell your shares	$	211	$	652	$	1,119	$	2,410
	sold all your shares at the end of the period	$	311	$	652	$	1,119	$	2,410

See the Appendix for additional hypothetical and expense information.

Your Account

CHOOSING A SHARE CLASS

The Fund offers three classes of shares in this prospectus — Class A, Class B and Class C. Each share class has its own commission and expense structure that affects the investment return of that class. Determining which share class is best for you depends on various factors, including the amount you are investing, how long you expect to hold your investment and your personal situation.

You should consult with your financial advisor before deciding which share class is most appropriate for you. The following considerations should be part of your assessment:

•  You will pay a commission if you buy Class A, B or C shares, either at the time of investment or redemption, or through ongoing distribution commission payments (Rule 12b-1 fees) made from your investment over time, or both.

•  Class A shares require an up-front commission payment, but pay lower ongoing Rule 12b-1 fees than Class B and Class C shares. Class B and Class C shares have no up-front commission paid by the shareholder but pay higher ongoing commissions (Rule 12b-1 fees), and a deferred commission is imposed on a redemption of Class B shares within six years after purchase, and a deferred commission is imposed on a redemption of Class C shares within one year of purchase. The differential between classes will vary depending on the actual investment return for any given period.

•  Class A shares can be more advantageous to an investor who intends to hold the shares for several years and invests an amount large enough to qualify for a reduced rate of initial sales commission, taking into account the commissions that investor may pay when redeeming shares of other classes. To project whether Class A shares might be more advantageous to you, you should consider, among other factors, the time period you intend to hold the shares, your initial sales commission and a comparison of the total annual expenses of Class A shares to the expenses of other share classes. Class A shares pay an ongoing annual commission (Rule 12b-1 fee) of up to 0.25% of the average value of the shares.

•  Class B shares are no longer offered to new investors. A Class B shareholder of the Fund whose account has a value of less than $50,000 (including for this purpose the combined value of all eligible accounts

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Your Account

maintained by that shareholder that would be used to determine eligibility for reduced sales charges on Class A shares) may purchase additional Class B shares of the Fund to increase the account value up to a maximum of $49,999; any additional investment by the shareholder in that Fund will be invested in Class A shares of the Fund, without regard to the normal investment minimum for Class A shares, but will be subject to the applicable Class A shares up-front commission. Class B shares pay an ongoing annual commission (Rule 12b-1 fee) of up to 0.75% of the average value of the shares and automatically convert to Class A shares after eight years.

•  Class C shares are generally more advantageous to an investor who intends to hold shares for only a few years. Class C shares pay an ongoing annual commission (Rule 12b-1 fee) of up to 1.00% of the average value of the shares.

•  If you invest $1 million or more, you can purchase Class A shares but not Class C shares.

The Fund also offers an additional class of shares, Class Z shares, exclusively to certain institutional and other eligible investors. Class Z shares are made available through a separate prospectus provided to eligible institutional and other investors.

HOW TO BUY SHARES

Your financial advisor can help you establish an appropriate investment portfolio, buy shares and monitor your investments. When the Fund receives your purchase request in "good form," your shares will be bought at the next calculated public offering price. "Good form" means that the Fund's transfer agent has all information and documentation it deems necessary to effect your order. For example "good form" may mean that you have properly placed your order with your financial advisor or the Fund's transfer agent has received your completed application, including all necessary signatures. The Fund reserves the right to refuse a purchase order for any reason, including if the Fund believes that doing so would be in the best interest of the Fund and its shareholders. The USA PATRIOT Act may require us to obtain certain personal information from that we will use to verify your identity. If you do not provide the information, we may n ot be able to open your account. If we are unable to verify your customer information, we reserve the right to close your account or take such other steps as we deem reasonable.

INVESTMENT MINIMUMS

The investment minimum for initial investments (by purchase, exchange or certain transfers) of Class A, B and C shares is $50,000. The investment minimum is applied at the class level. For group retirement plans, the investment minimum is determined based on the amount of the plan's investment rather than that of its individual participants. The Fund may establish exclusions from the investment minimum from time to time that it deems appropriate and consistent with the interests of shareholders. Please see the SAI for details on these exclusions. The Fund reserves the right to change these investment minimums.

The Fund also reserves the right to refuse a purchase order for any reason, including if it believes that doing so would be in the best interest of the Fund and its shareholders. Finally, pursuant to the Trust's Agreement and Declaration of Trust, the Fund reserves the right to redeem your shares if your account falls below the minimum investment requirements.

Please see the SAI for more details on investment minimums.

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Your Account

Outlined below are the various options for buying shares:

Method	Instructions
Through your financial advisor	Your financial advisor can help you establish your account and buy Fund shares on your behalf. To receive the current trading day's price, your financial advisor must receive your request prior to the close of regular trading on the New York Stock Exchange (NYSE), usually 4:00 p.m. Eastern time. Your financial advisor may charge you fees for executing the purchase for you.
By check (new account)	For new accounts, send a completed application and check made payable to the Fund to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By check (existing account)	For existing accounts, fill out and return the additional investment stub included in your account statement, or send a letter of instruction including your Fund name and account number with a check made payable to the Fund to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By exchange	You or your financial advisor may acquire Fund shares for your account by exchanging shares you own in a different fund distributed by Columbia Management Distributors, Inc. for shares of the same class (and, in some cases, certain other classes) of the Fund at no additional cost. An exchange to another fund may incur a sales charge if the original purchase was not assessed a sales charge. To exchange by telephone, call 1-800-422-3737. Please see "How to Exchange Shares" for more information.
By wire	You may purchase Fund shares by wiring money from your bank account to your Fund account. To wire funds to your Fund account, call 1-800-422-3737 for wiring instructions.
By electronic funds transfer	You may purchase Fund shares by electronically transferring money from your bank account to your Fund account by calling 1-800-422-3737. An electronic funds transfer may take up to two business days to settle and must be considered in "good form." You must set up this feature prior to your telephone request. Be sure to complete the appropriate section of the application for this feature.
Automatic investment plan	You may make monthly or quarterly investments ($50 minimum) automatically from your bank account to your Fund account. You may select a pre-authorized amount to be sent via electronic funds transfer. Be sure to complete the appropriate section of the application for this feature.
Automated dollar cost averaging	You may purchase Fund shares for your account by exchanging $100 or more each month from another fund for shares of the same class of the Fund at no additional cost. Exchanges will continue so long as your fund balance is sufficient to complete the transfers. You may terminate your program or change the amount of the exchange (subject to the $100 minimum) by calling 1-800-345-6611. There may be an additional sales charge if exchanging from a money market fund. Be sure to complete the appropriate section of the account application for this feature.
By dividend diversification	You may automatically invest dividends distributed by another fund into the same class of shares (and, in some cases, certain other classes) of the Fund at no additional sales charge. There may be an additional sales charge if automatically investing dividends from a money market fund. To invest your dividends in the Fund, call 1-800-345-6611.
Through the internet	You may purchase Fund shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet purchases. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

SALES CHARGES (COMMISSIONS)

You may be subject to an initial sales charge when you purchase, or a contingent deferred sales charge (CDSC) when you sell, shares of the Fund. These sales charges are described below. In certain circumstances, the sales charge may be reduced or waived, as described below and in the SAI.

Rule 12b-1 Plan The Fund has adopted a plan under Rule 12b-1 under the Investment Company Act that permits it to pay its distributor ongoing sales and marketing fees (commissions) to support the sale and distribution of Class A, B and C shares and certain services provided to you by your financial advisor, and your financial advisor may receive all or a portion of those fees attributable to your shares. The annual fee, as a percentage of the value of the shares, is normally 0.25% for Class A, 0.75% for Class B and 1.00% for Class C shares. These fees are paid out of

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Your Account

the assets of these share classes. Over time, these fees reduce the return on your investment. Class B shares automatically convert to Class A shares after eight years, eliminating a portion of the Rule 12b-1 fee thereafter.

Financial Intermediary Payments

The Fund's distributor, investment adviser or their affiliates may make payments, from their own resources, to certain financial intermediaries, including other Bank of America affiliates, for marketing support services. For purposes of this section the term "financial intermediary" includes any broker, dealer, bank, bank trust department, registered investment adviser, financial planner, retirement plan or other third-party administrator and any other institution having a selling, services or any similar agreement with the Fund's distributor, investment adviser or one of their affiliates. These payments are generally based upon one or more of the following factors: average net assets of the mutual funds distributed by the Fund's distributor attributable to that financial intermediary, gross sales of the mutual funds distributed by the Fund's distributor attributable to that financial intermediary, reimbursement of ticket charge s (fees that a financial intermediary firm charges its representatives for effecting transactions in fund shares) or a negotiated lump sum payment.

While the financial arrangements may vary for each financial intermediary, the support payments to any one financial intermediary are generally expected to be between 0.05% and 0.35% on an annual basis for payments based on average net assets of the Fund attributable to the financial intermediary, and between 0.10% and 0.25% on an annual basis for firms receiving a payment based on gross sales of the Fund attributable to the financial intermediary. The Fund's distributor, investment adviser or their affiliates may make payments in materially larger amounts or on a basis materially different from those described above when dealing with other affiliates of Bank of America. Such increased payments to the other Bank of America affiliate may enable the other Bank of America affiliate to offset credits that it may provide to its customers in order to avoid having such customers pay fees to multiple Bank of America entities in connecti on with the customer's investment in the Fund.

Payments also may be made to certain financial intermediaries, including other Bank of America affiliates, that provide investor services to retirement plans and other investment programs to compensate financial intermediaries for services they provide to such programs, including, but not limited to, sub-accounting, sub-transfer agency, similar shareholder or participant recordkeeping, shareholder or participant reporting, or shareholder or participant transaction processing. These payments for investor servicing support vary by financial intermediary but generally are not expected, with certain limited exceptions, to exceed 0.35% of the total Fund assets for Class A, B and C shares in the program on an annual basis.

The Trust's Board of Trustees has authorized the Fund to pay to any intermediary up to 0.05% of the average aggregate value of Fund shares in the intermediary's program on an annual basis for providing investor services. Charges of an intermediary in excess of that paid by the Fund will be borne by the Fund's distributor or its affiliates.

The Fund's distributor, investment adviser or their affiliates may make other payments or allow promotional incentives to financial intermediaries to the extent permitted by the rules of the Securities and Exchange Commission, the National Association of Securities Dealers and by other applicable laws and regulations.

Amounts paid by the Fund's distributor, investment adviser or their affiliates are paid out of the distributor's, investment adviser's or their affiliates' own resources and do not increase the amount paid by you or the Fund. You can find further details about the payments made by the Fund's distributor, investment adviser or their affiliates and the services provided by financial intermediaries as well as a list of the financial intermediaries to

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Your Account

which the Fund's distributor, investment adviser or their affiliates have agreed to make marketing support payments in the Fund's SAI, which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611. Your financial intermediary may charge you fees or commissions in addition to those disclosed in this prospectus. You can ask your financial intermediary for information about any payments it receives from the Fund's distributor, investment adviser and their affiliates and any services your financial intermediary provides, as well as fees and/or commissions it charges. In addition, depending on the financial arrangement in place at any particular time, a financial intermediary and its financial consultants also may have a financial incentive for recommending a particular f und or share class over others. You should consult with your financial adviser and review carefully any disclosure by the financial intermediary as to compensation received by your financial adviser.

Class A shares Your purchases of Class A shares are made at the public offering price for these shares. This price includes a sales charge that is based on the amount of your initial investment when you open your account. The sales charge you pay on an additional investment is based on the total amount of your purchase and the current value of your account. Shares you purchase with reinvested dividends or other distributions are not subject to a sales charge. A portion of the sales charge is paid as a commission to your financial advisor on your purchase of Class A shares. The amount of the sales charge differs depending on the amount you invest as shown in the table below.

Class A Sales Charges

	Sales Charge as % of:				% of offering price
Amount of purchase*	offering price		net amount invested		retained by your financial advisor
Less than $50,000**		5.75		6.10		5.00
$50,000 to less than $100,000		4.50		4.71		3.75
$100,000 to less than $250,000		3.50		3.63		2.75
$250,000 to less than $500,000		2.50		2.56		2.00
$500,000 or more		2.00		2.04		1.75

*  Mutual fund wrap programs and group retirement plans that invest $50,000 or more in Class A shares of the Fund will not be subject to a sales charge. Discretionary wrap programs that invest directly in the Fund, trade on an omnibus basis and were invested in the Fund prior to August 5, 2005 are subject to the $50,000 investment minimum.

**  Initial purchases of less than $50,000 are no longer accepted. However, for accounts opened prior to August 5, 2005, subsequent investments that do not meet the Fund's current investment minimum will be accepted.

In addition to the initial sales charge paid to your financial advisor and distributor, a 0.25% annual commission is paid to your financial advisor over the life of your investment out of your Fund assets as a 12b-1 fee.

The Fund's distributor may also pay additional compensation to financial advisors as an incentive for promoting the sale of shares of funds that it distributes.

Class A shares bought without an initial sales charge in accounts aggregating $1 million to $50 million at the time of purchase are subject to a 1.00% CDSC if the shares are sold within 12 months of the time of purchase. Subsequent Class A share purchases that bring your account value above $1 million (but less than $50 million) are subject to a CDSC if redeemed within 12 months of the date of purchase. The 12-month period begins on the first day of the month in which the purchase was made. The CDSC does not apply to retirement plans purchasing shares through a fee-based program.

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Your Account

For Class A share purchases of $1 million or more, financial advisors receive a cumulative commission from the distributor as follows:

Purchases Over $1 Million

Amount purchased	Commission %
$1 million to less than $3 million		1.00
$3 million to less than $50 million		0.50
$50 million or more		0.25

For group retirement plans, financial advisors are eligible to receive a 1.00% commission from the distributor on purchases, including those in amounts less than $1 million, that are coded as commission eligible trades. In determining the commission payable to a financial advisor in the above table, the breakpoint discount policies described in "Reduced Sales Charges (Commissions) for Larger Investments," below, shall apply.

UNDERSTANDING CONTINGENT DEFERRED SALES CHARGES (COMMISSIONS)

Certain investments in Class A, B and C shares are subject to a CDSC, a sales charge applied at the time you sell your shares. You will pay the CDSC only on shares you sell within a certain amount of time after purchase. The CDSC generally declines each year until there is no charge for selling shares. The CDSC is applied to the net asset value at the time of purchase or sale, whichever is lower. For purposes of calculating the CDSC, the start of the holding period is the first day of the month in which the purchase was made. Shares you purchase with reinvested dividends or other distributions are not subject to a CDSC. When you place an order to sell shares, the Fund will automatically sell first those shares not subject to a CDSC and then those you have held the longest.

Reduced Sales Charges ("Commissions") for Larger Investments.

A.  What are the principal ways to obtain a breakpoint discount?

There are two principal ways you may pay a lower sales charge (often referred to as "breakpoint discounts") when purchasing Class A shares of the Fund and other funds in the Columbia family of funds.

Rights of Accumulation The value of eligible accounts maintained by you and each member of your immediate family may be combined with the value of your current purchase to reach a sales charge discount level (according to the chart on the previous page) and to obtain the lower sales charge for your current purchase. To calculate the combined value of the accounts, the Fund will use the shares' current public offering price.

Statement of Intent You also may pay a lower sales charge when purchasing Class A shares by signing a Statement of Intent. By doing so, you would be able to pay the lower sales charge on all purchases made under the Statement of Intent within 13 months. As described in the chart on the previous page, the first breakpoint discount will be applied when total purchases reach $50,000. If your Statement of Intent purchases are not completed within 13 months, you will be charged the applicable sales charge on the amount you had invested to that date. To calculate the total value of your Statement of Intent purchases, the Fund will use the historic cost (i.e. dollars invested) of the shares held in each eligible account. You must retain all records necessary to substantiate historic costs because the Fund and your financial intermediary may not maintain this information.

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Your Account

B.  What accounts are eligible for breakpoint discounts?

The types of eligible accounts that may be aggregated to obtain one or both of the breakpoint discounts described above include:

•  Individual accounts

•  Joint accounts

•  Certain IRA accounts

•  Certain trusts

•  UTMA/UGMA accounts

For the purposes of obtaining a breakpoint discount, members of your "immediate family" include your spouse, parent, stepparent, legal guardian, child, stepchild, father-in-law and mother-in-law. Eligible accounts include those registered in the name of your dealer or other financial intermediary through which you own Columbia fund shares. An account is not eligible to the extent it holds an institutional class of shares of a Columbia money market fund or Class R shares of any Columbia fund. The value of your investment in a non-institutional class of a Columbia money market fund held in an eligible account may be aggregated with your investments in other funds in the Columbia family of funds to obtain a breakpoint discount through a Right of Accumulation. Non-institutional class investments in Columbia money market funds may also be included in the aggregation for a Statement of Intent for shares that have been charged a commis sion.

C.  How do I obtain a breakpoint discount?

The steps necessary to obtain a breakpoint discount depend on how your account is maintained with the Columbia family of funds. To obtain any of the above breakpoint discounts, you must notify your financial advisor at the time you purchase shares of the existence of each eligible account maintained by you or your immediate family. It is the sole responsibility of your financial advisor to ensure that you receive discounts for which you are eligible, and the Fund is not responsible for a financial advisor's failure to apply the eligible discount to your account. You may be asked by the Fund or your financial advisor for account statements or other records to verify your discount eligibility, including, where applicable, records for accounts opened with a different financial advisor and records of accounts established by members of your immediate family. If you own shares exclusively through an account maintained with the Fund's transfer agent, Columbia Management Services, Inc., you will need to provide the foregoing information to a Columbia Management Services, Inc. representative at the time you purchase shares.

D.  How can I obtain more information about breakpoint discounts?

Certain investors, including affiliates of the Fund, broker/dealers and their affiliates, investors in wrap-fee programs through fee-based advisers or certain retirement plans, certain shareholders of funds that were reorganized into other Columbia funds, and investors using the proceeds of redemptions of Fund shares or of certain Bank of America trust or similar accounts, may purchase shares at a reduced sales charge or net asset value, which is the value of a fund share excluding any sales charges. CDSCs may also be waived for redemptions under a systematic withdrawal program, in connection with the death or post-purchase disability of a shareholder, certain medical expenses, charitable gifts, involuntary and tax-related redemptions, or when the selling broker/dealer has agreed to waive or return its commission. Restrictions may apply to certain accounts and certain

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Your Account

transactions. Further information regarding these discounts may be found in the Fund's SAI, which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611.

Class B shares Your purchases of Class B shares are at Class B's net asset value. No new Class B share accounts may be established in the Fund. However, Class B share accounts established prior to August 5, 2005, may nonetheless purchase additional Class B shares, so long as those purchases do not result in the account holding $50,000 or more of Class B shares (including for this purpose the combined value of all eligible accounts maintained by you that would be used to determine eligibility for reduced sales charges on Class A shares). In the event that an existing Class B shareholder seeks to add funds to such an account so that the balance would be in excess of $49,999, the amount in excess may be invested in Class A shares without the imposition of the minimum investment requirement for Class A shares. Such purchases of Class A shares will be subj ect to the applicable sales load imposed on such purchases. See "Class A Sales Charges" on page 11.

Class B shares have no front-end sales charge, but they do carry a CDSC that is imposed only on shares sold within six years of purchase. The CDSC declines over the six years and disappears in the seventh year. The distributor pays your financial advisor an up-front commission on sales of Class B shares as described in the chart below. In addition, Class B shares bear ongoing service and distribution fees that are higher than those borne by Class A shares.

Purchases of less than $50,000⁽¹⁾:

Class B Sales Charges

Holding period after purchase	% deducted when shares are sold(2)
Through first year		5.00
Through second year		4.00
Through third year		3.00
Through fourth year		3.00
Through fifth year		2.00
Through sixth year		1.00
Longer than six years		0.00

(1)  Only applicable to accounts opened prior to August 5, 2005.

(2)  Applied to the net asset value at the time of purchase or sale, whichever is lower.

In addition, from the annual fee of 0.75% of the value of your shares paid out of your Fund assets as Rule 12b-1 fees, the distributor receives 0.50% of the value of the shares for each of the first eight years, or an aggregate 4.00% over eight years, which will offset the commission it paid to your financial advisor. Your financial advisor is paid the remaining 0.25% as an ongoing commission for the life of your investment.

The conversion of Class B shares to Class A shares occurs automatically eight years after purchase.

Class C shares Your purchases of Class C shares are at Class C's net asset value. Although Class C shares have no front-end sales charge, they carry a CDSC of 1.00% that is applied to shares sold within the first year after they are purchased. After holding shares for one year, you may sell them at any time without paying a CDSC. The distributor pays your financial advisor an up-front commission of 1.00% on your purchase of Class C shares, for which the distributor is repaid from the ongoing annual fee of 1.00% of the value of your shares paid out of your Fund assets as Rule 12b-1 fees, which is higher than the Rule 12b-1 fees borne by Class A and Class B shares.

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Class C Sales Charges

Holding period after purchase	% deducted when shares are sold(1)
Through one year		1.00
Longer than one year		0.00

(1)  Applied to the net asset value at the time of purchase or sale, whichever is lower.

A 1.00% annual commission is paid to your financial advisor and the distributor over the life of your investment out of your Fund assets.

HOW TO EXCHANGE SHARES

You may exchange your shares for shares of the same share class (and in some cases, certain other classes) of another fund distributed by Columbia Management Distributors, Inc. at net asset value. If your shares are subject to a CDSC, you will not be charged a CDSC upon the exchange. However, when you sell the shares acquired through the exchange, the shares sold may be subject to a CDSC, depending upon when you originally purchased the shares you are exchanging. For purposes of computing the CDSC, the length of time you have owned your shares will be computed from the date of your original purchase and the applicable CDSC will be the CDSC of the original fund. Shareholders of Columbia Acorn Funds that qualify to purchase Class A shares at net asset value may exchange their Class A shares for Class Z shares of another fund distributed by Columbia Management Distributors, Inc. (see the SAI for a description of these situations). Unless your account is part of a tax-deferred retirement plan, an exchange is a taxable event, and you may realize a gain or a loss for tax purposes. The Fund may terminate your exchange privilege if the adviser determines that your exchange activity is likely to adversely impact its ability to manage the Fund. See "Fund Policy on Trading of Fund Shares" for the Fund's policy. To exchange by telephone, call 1-800-422-3737. Please have your account and taxpayer identification numbers available when calling.

You also may exchange your shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet exchanges. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

HOW TO SELL SHARES

Your financial advisor can help you determine if and when you should sell your shares. You may sell shares of the Fund on any regular business day that the NYSE is open.

When the Fund receives your sales request in "good form," shares will be sold at the next calculated net asset value. "Good form" means that the Fund's transfer agent has all information and documentation it deems necessary to effect your order. For example, when selling shares by letter of instruction, "good form" means (i) your letter has complete instructions, the proper signatures and Medallion Signature Guarantees, (ii) if applicable, you have included any certificates for shares to be sold, and (iii) any other required documents are attached. For additional documents required for sales by corporations, agents, fiduciaries, surviving joint owners and other legal entities, please call 1-800-345-6611. Retirement plan accounts have special requirements; please call 1-800-799-7526 for more information.

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Your Account

The Fund will generally send proceeds from the sale to you within seven days (usually on the next business day after your request is received in "good form"). However, if you purchased your shares by check, the Fund may delay sending the proceeds from the sale of your shares for up to 10 days after your purchase to protect against checks that are returned. No interest will be paid on uncashed redemption checks. Redemption proceeds may be paid in securities rather than cash, under certain circumstances. For more information, see the paragraph "Non-Cash Redemptions" under the section "How to Sell Shares" in the SAI.

During any 90-day period for any one shareholder, the Fund is obligated to redeem shares solely in cash up to the lesser of $250,000 or 1% of the Fund's net assets. Redemptions in excess of these limits will normally be paid in cash, but may be paid wholly or partly by an in-kind distribution of securities.

Outlined below are the various options for selling shares:

Method	Instructions
Through your financial advisor	You may call your financial advisor to place your sell order. To receive the current trading day's price, your financial advisor must receive your request prior to the close of regular trading on the NYSE, usually 4:00 p.m. Eastern time. Your financial advisor may charge you fees for executing a redemption for you.
By exchange	You or your financial advisor may sell Fund shares by exchanging from the Fund into the same share class (and, in some cases, certain other classes) of another fund distributed by Columbia Management Distributors, Inc. at no additional cost. To exchange by telephone, call 1-800-422-3737.
By telephone	You or your financial advisor may sell Fund shares by telephone and request that a check be sent to your address of record by calling 1-800-422-3737, unless you have notified the Fund of an address change within the previous 30 days. The dollar limit for telephone sales is $100,000 in a 30-day period. You do not need to set up this feature in advance of your call. Certain restrictions apply to retirement accounts. For details, call 1-800-799-7526.
By mail	You may send a signed letter of instruction or, if applicable, stock power form along with any share certificates to be sold to the address below. In your letter of instruction, note the Fund's name, share class, account number, and the dollar value or number of shares you wish to sell. All account owners must sign the letter. Signatures must be guaranteed by either a bank, a member firm of a national stock exchange or another eligible guarantor that participates in the Medallion Signature Guarantee Program for amounts over $100,000 or for alternate payee or mailing instructions. Additional documentation is required for sales by corporations, agents, fiduciaries, surviving joint owners and individual retirement account owners. For details, call 1-800-345-6611. Mail your letter of instruction to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By wire	You may sell Fund shares and request that the proceeds be wired to your bank. You must set up this feature prior to your request. Be sure to complete the appropriate section of the account application for this feature. Generally, the value of your redemption must be at least equal to $500 in order to have the sale proceeds wired to your bank. There is a $7.50 charge for wiring sale proceeds to your bank. (The transfer agent may waive this fee for omnibus and nominee accounts.) Your bank may charge additional fees for such wire transfer.
By systematic withdrawal plan	You may automatically sell a specified dollar amount or percentage of your account on a monthly, quarterly or semiannual basis and have the proceeds sent to you if your account balance is at least $5,000. The $5,000 minimum account balance requirement is waived for wrap accounts. This feature is not available if you hold your shares in certificate form. All dividend and capital gains distributions must be reinvested. Be sure to complete the appropriate section of the account application for this feature.
By electronic funds transfer	You may sell Fund shares and request that the proceeds be electronically transferred to your bank. Proceeds may take up to two business days to be received by your bank. You must set up this feature prior to your request. Be sure to complete the appropriate section of the account application for this feature.
Through the internet	You may sell Fund shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet redemptions. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

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Your Account

FUND POLICY ON TRADING OF FUND SHARES

The interests of the Fund's long-term shareholders may be adversely affected by certain short-term trading activity by Fund shareholders. Such short-term trading activity, when excessive, has the potential to interfere with efficient portfolio management, generate transaction and other costs, dilute the value of Fund shares held by long-term shareholders and have other adverse effects on the Fund. This type of excessive short-term trading activity is referred to herein as "market timing." For purposes of this section, the "Columbia Funds" are the Columbia, Columbia Acorn Trust and Wanger Advisors Trust families of mutual funds. The Columbia Funds are not intended as vehicles for market timing. The Board of Trustees of the Fund has adopted the policies and procedures set forth below with respect to frequent trading of the Fund's shares.

The Fund, directly and through its agents, takes various steps designed to deter and curtail market timing. For example, if the Fund detects that any shareholder has conducted two "round trips" (as defined below) in the Fund in any 28-day period, except as noted below with respect to orders received through omnibus accounts, the Fund will reject the shareholder's future purchase orders, including exchange purchase orders, involving any Columbia fund (other than a money market fund). In addition, if the Fund determines that any person, group or account has engaged in any type of market timing activity (independent of the two-round-trip limit), the Fund may, in its discretion, reject future purchase orders by the person, group or account, including exchange purchase orders, involving the same or any other Columbia fund, and also retains the right to modify these market timing policies at any time without prior notice.

The rights of shareholders to redeem shares of the Fund are not affected by any of the limits mentioned above. However, certain funds (other than the Fund) impose a redemption fee on the proceeds of shares that are redeemed or exchanged within 60 days of their purchase.

For these purposes, a "round trip" is a purchase by any means into a Columbia fund followed by a redemption, of any amount, by any means out of the same Columbia fund. Under this definition, an exchange into the Fund followed by an exchange out of the Fund is treated as a single round trip. Also for these purposes, where known, accounts under common ownership or control generally will be counted together. Accounts maintained or managed by a common intermediary, such as an adviser, selling agent or trust department, generally will not be considered to be under common ownership or control.

Purchases, redemptions and exchanges made through the Columbia Funds' Automatic Investment Plan, Systematic Withdrawal Plan or similar automated plans are not subject to the two-round-trip limit. Purchases, redemptions and exchanges made by Columbia Thermostat Fund are also not subject to the two round-trip limit. The two-round-trip limit may be modified for, or may not be applied to, accounts held by certain retirement plans to conform to plan limits, considerations relating to the Employee Retirement Income Security Act of 1974 or regulations of the Department of Labor, and for certain asset allocation or wrap programs.

The practices and policies described above are intended to deter and curtail market timing in the Fund. However, there can be no assurance that these policies, individually or collectively, will be totally effective in this regard because of various factors. In particular, a substantial portion of purchase, redemption and exchange orders are received through omnibus accounts. Omnibus accounts, in which shares are held in the name of an intermediary on behalf of multiple beneficial owners, are a common form of holding shares among financial intermediaries and retirement plans. The Fund typically is not able to identify trading by a particular beneficial owner through an omnibus account, which may make it difficult or impossible to determine if a particular account is engaged in market timing. Consequently, there is

17

Your Account

the risk that the Fund may not be able to identify, deter or curtail certain market timing do anything in response to market timing that occurs in the Fund, which may result in certain shareholders being able to market time the Fund while the shareholders in the Fund bear the burden of such activities.

Certain financial intermediaries (including certain retirement plan service providers whose clients include, among others, various retirement plans sponsored by Bank of America and its affiliates for the benefit of its employees (the "Bank of America retirement plan service providers")) have different policies regarding monitoring and restricting market timing in the underlying beneficial owner accounts that they maintain through an omnibus account that may be more or less restrictive than the Fund practices discussed above. In particular, the Bank of America retirement plan service providers permit the reinstatement of future purchase orders for shares of the Fund following various suspension periods. If an intermediary does not enforce the Fund's policy, the intermediary must either provide data transparency to Columbia Management or Columbia Management must determine that the intermediary's policy taken in its entirety provid es protections to Fund shareholders that are generally commensurate with the Fund's policy.

The Fund seeks to act in a manner that it believes is consistent with the best interests of Fund shareholders in making any judgments regarding market timing. Neither the Fund nor its agents shall be held liable for any loss resulting from rejected purchase orders or exchanges.

OTHER INFORMATION ABOUT YOUR ACCOUNT

How the Fund's Share Price is Determined The price of each class of the Fund's shares is based on its net asset value. The net asset value is determined at the close of regular trading on the NYSE, usually 4:00 p.m. Eastern time, on each business day that the NYSE is open for trading (typically Monday through Friday). Net asset value is not determined on days on which the NYSE is closed for trading.

When you request a transaction, it will be processed at the net asset value per share (plus any applicable sales charges) next determined after your request is received in "good form" by the distributor. In most cases, in order to receive that day's price, the distributor must receive your order before that day's transactions are processed. If you request a transaction through your financial advisor, your financial advisor must receive your order by the close of trading on the NYSE to receive that day's price.

The Fund determines its net asset value for each share class by dividing each class's total net assets by the number of that class's outstanding shares. In determining the net asset value, the Fund must determine the value of each security in its portfolio at the close of each trading day. Securities for which market quotations are available are valued each day at the current market value. However, where market quotations are unavailable, or when the adviser believes that subsequent events have made them unreliable, the Fund may use other data to determine the fair value of the securities.

The Fund has retained an independent statistical fair value pricing service to assist in the fair valuation process for securities principally traded in a foreign market in order to adjust for possible changes in value that may occur between the close of the foreign exchange and the time at which Fund shares are priced. The use of an independent fair value pricing service is intended to and may decrease the opportunities for time zone arbitrage transactions. There can be no assurance that the use of an independent fair value pricing service will successfully decrease arbitrage opportunities. If a security is valued at a "fair value," that value may be different from the last quoted market price for the security.

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Your Account

You can find the daily prices of some share classes for the Fund in most major daily newspapers under the heading of "Columbia." You can find daily prices for all share classes by visiting www.columbiafunds.com.

Share Certificates Share certificates are not available for any class of shares offered by the Fund. If you currently hold previously issued share certificates, you will not be able to sell your shares until you have returned your share certificates to the transfer agent.

Dividends, Distributions, and Taxes The Fund has the potential to make the following distributions:

Types of Distributions

Dividends	Represents interest and dividends earned from securities held by the Fund, net of expenses incurred by the Fund.
Capital gains	Represents net long-term capital gains on sales of securities held for more than one year and net short-term capital gains, which are gains on sales of securities held for a one-year period or less.

Distribution Options The Fund distributes any dividends in June and December and any capital gains (including short-term capital gains) at least annually. You can choose one of the options listed in the table below for these distributions when you open your account. To change your distribution option call 1-800-345-6611.

If you do not indicate on your application or at the time your account is established your preference for handling distributions, the Fund will automatically reinvest all distributions in additional shares of the Fund.

UNDERSTANDING FUND DISTRIBUTIONS

The Fund may earn income from the securities it holds. The Fund also may realize capital gains or losses on sales of its securities. The Fund intends to distribute substantially all of its net investment income and capital gains to shareholders each year. As a shareholder, you are entitled to a portion of the Fund's income and capital gains based on the number of shares you own at the time these distributions are declared.

Distribution Options

Reinvest all distributions in additional shares of the Fund

Reinvest all distributions in shares of another fund

Receive dividends in cash (see options below) and reinvest capital gains

Receive all distributions in cash (with one of the following options):

•  send the check to your address of record

•  send the check to a third-party address

•  transfer the money to your bank via electronic funds transfer

Distributions of $10 or less will automatically be reinvested in additional Fund shares. If you elect to receive distributions by check and the check is returned as undeliverable, all subsequent distributions will be reinvested in additional shares of the Fund.

Taxes Unless you are an entity exempt from income taxes or invest under a retirement account, regardless of whether you receive your distributions in cash or reinvest them in additional Fund shares, all Fund distributions are subject to federal income tax. Depending on the state where you live, distributions also may be subject to state and local income taxes.

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Your Account

The Fund intends to elect to be treated and to qualify each year as a regulated investment company. A regulated investment company is not subject to tax at the corporate level on income and gains from investments that are distributed to shareholders in accordance with applicable law. However, the Fund's failure to qualify as a regulated investment company could result in corporate level taxation, and consequently, a reduction in income available for distribution to shareholders.

In general, any distributions of dividends, interest and short-term capital gains (determined by how long the Fund held the investments that generated them) are taxable as ordinary income, unless such dividends are "qualified dividend income" (as defined in the Internal Revenue Code) eligible for a reduced rate of tax. Properly designated distributions of long-term capital gains (determined by how long the Fund held the investments that generated them) are generally taxable as such, regardless of how long you have held your Fund shares. You will be provided with information each year regarding the amount of ordinary income and capital gains distributed to you for the previous year and any portion of your distribution which is exempt from state and local taxes. Long-term capital gain rates have been reduced — in general, to 15% with lower rates applying to taxpayers in the 10% and 15% rate brackets — for taxable years b eginning before January 1, 2011. Distributions are taxable to you even if they are paid from income or gains earned by the Fund before you made your investment (and thus were included in the price you paid). Your investment in the Fund may have additional personal tax implications. Please consult your tax advisor about foreign, federal, state, local or other applicable tax laws.

In addition to the dividends and capital gains distributions made by the Fund, you may realize a capital gain or loss when selling or exchanging shares of the Fund. Such transactions also may be subject to federal, state and local income tax.

Board of Trustees

The Fund is governed by its Board of Trustees. More than 75% of the Fund's Trustees are independent, meaning that they have no affiliation with the adviser or the Funds, apart from their positions as Trustees and the personal investments they may have made as private individuals.

The independent Trustees bring backgrounds in business and the professions and academia to their task of working with the Funds' officers to establish the policies and oversee the activities of the Funds. Among the Trustees' responsibilities are selecting the investment adviser for the Funds; negotiating the advisory agreements; reviewing other contracts; approving investment policies; monitoring Fund operations, performance, and costs; and nominating or selecting new Trustees.

Each Trustee serves until his or her retirement, resignation, death or removal; or otherwise as specified in the Trust's organizational documents. It is expected that every five years the Trustees will call a meeting of shareholders to elect Trustees. A Trustee must retire at the end of the year in which he or she attains the age of 75. Any Trustee may be removed at a shareholders' meeting by a vote representing two-thirds of the net asset value of all shares of the Funds of the Trust. The mailing address for the Trustees and officers is 227 W. Monroe, Suite 3000, Chicago, Illinois 60606.

For more detailed information on the Board of Trustees, please refer to the SAI.

20

Managing the Fund

INVESTMENT ADVISER

Columbia Wanger Asset Management, L.P. (CWAM), located at 227 West Monroe Street, Suite 3000, Chicago, Illinois 60606, is the Fund's investment adviser and is responsible for the Fund's management, subject to the oversight of the Fund's Board of Trustees. CWAM and its predecessor have managed mutual funds, including the Fund, since 1992. In its duties as investment adviser, CWAM runs the Fund's day-to-day business, including making investment decisions and placing all orders for the purchase and sale of the Fund's portfolio securities.

CWAM was previously named Liberty Wanger Asset Management, L.P. and its predecessor was named Wanger Asset Management, L.P. (WAM). CWAM is a wholly owned subsidiary of Columbia Management Group, LLC, which is an indirect wholly owned subsidiary of Bank of America Corporation. As of December 31, 2006, CWAM managed more than $32.9 billion in assets.

CWAM's advisory fee for managing the Fund in 2006 was 0.82% of the Fund's average daily net assets. CWAM also received an administrative fee from the Fund in 2006 of 0.04% of the Fund's average daily net assets. A discussion of the factors considered by the Fund's Board of Trustees in approving the Fund's investment advisory contract is included in the Fund's annual report to shareholders for the period ended December 31, 2006.

PORTFOLIO MANAGER

CWAM uses a team to assist the lead portfolio manager in managing the Fund. Team members share responsibility for providing ideas, information and knowledge in managing the Fund, and each team member has one or more particular areas of expertise. The portfolio manager is responsible for making daily investment decisions and utilizing the management team's input and advice when making buy and sell determinations.

Ben AndrewsLead portfolio manager

Ben Andrews has managed Columbia Acorn Select since March 2004. He is a vice president of the Trust and has been part of the CWAM investment team since 1998, most recently as a senior technology analyst. His analytical experience includes covering a broad range of industries and special situations. Mr. Andrews also is a vice president of Wanger Advisors Trust and the lead portfolio manager of Wanger Select, a mutual fund underlying variable insurance products.

The SAI provides additional information about the portfolio manager's compensation, other accounts managed and ownership of securities in the Fund.

LEGAL PROCEEDINGS

The Trust, CWAM and the trustees of the Trust (collectively, the "Columbia defendants") are named as defendants in class and derivative complaints, which were consolidated in a Multi-District Action in the federal district court for the District of Maryland on February 20, 2004 (the "MDL Action"). These lawsuits contend that defendants permitted certain investors to market time their trades in certain Columbia Acorn Funds. The MDL Action is ongoing. All claims against the Acorn Trust and its independent trustees have been dismissed; however, the interested trustees of the Trust are still parties to the MDL Action.

On March 21, 2005, a class action complaint was filed against the Trust in the Superior Court of the Commonwealth of Massachusetts seeking to rescind the contingent deferred sales charges assessed upon redemption of Class B shares of Columbia Acorn Funds due to the alleged market timing of the Columbia Acorn Funds. In addition to the rescission of sales charges, plaintiffs seek recovery of actual damages, attorneys' fees and costs. The case has been transferred to the MDL Action in the federal district court of Maryland.

21

Managing the Fund

The Trust and CWAM are also defendants in a class action lawsuit, filed on November 13, 2003 in the Circuit Court of the Third Judicial Circuit, Madison County, Illinois, that alleges, in summary, that the Trust and CWAM exposed shareholders of Columbia Acorn International to trading by market timers by allegedly (a) failing to properly evaluate daily whether a significant event affecting the value of that fund's securities had occurred after foreign markets had closed but before the calculation of the fund's net asset value (b) failing to implement the fund's portfolio valuation and share pricing policies and procedures; and (c) failing to know and implement applicable rules and regulations concerning the calculation of net asset value ("Fair Valuation Lawsuit"). On April 5, 2005, the United States Court of Appeals for the Seventh Circuit ruled that the plaintiffs' state law claims were preempted under federal law resulting in the dismissal of plaintiffs' complaint. Plaintiffs appealed the Seventh Circuit's ruling to the United States Supreme Court. On June 15, 2006, the Supreme Court reversed the Seventh Circuit's ruling on jurisdictional grounds, and the case ultimately was remanded to the state court.

On April 4, 2006, the plaintiffs and the Columbia defendants named in the MDL Action executed an agreement in principle intended to fully resolve all of the lawsuits consolidated in the MDL Action as well as the Fair Valuation Lawsuit. The court entered a stay after the parties executed a the agreement in principle. The settlement is subject to court approval.

In 2004, CWAM and the trustees of the Columbia Acorn Trust were named as defendants in certain purported shareholder class and derivative actions making claims, including claims under the Investment Company and the Investment Advisers Acts of 1940 and state law. Certain Columbia Acorn Funds were named as nominal defendants. The suits allege, inter alia, that the fees and expenses paid by the funds are excessive and that the funds' advisers and their affiliates inappropriately used fund assets to distribute the funds and for other improper purposes. On March 2, 2005, the actions were consolidated in the Massachusetts federal court as In re Columbia Entities Litigation. The plaintiffs filed a consolidated amended complaint on June 9, 2005. On November 30, 2005, the judge dismissed all claims by plaintiffs and entered final judgment in favor of the defendants. The plaintiffs appealed to the United States Court of Appeals for the First Circuit on December 30, 2005. A stipulation and settlement agreement dated January 19, 2007 was filed in the First Circuit on February 14, 2007, with a joint stipulation of dismissal and motion for remand to obtain district court approval of the settlement. The joint motion was granted and the appeal was dismissed. On March 6, 2007, the case was remanded to the District Court, where the parties will seek court approval of the settlement. The terms of the proposed settlement, if approved, will require payments by the funds' adviser and/or its affiliates, including payment of plaintiffs' attorneys' fees and notice to class members. In the event that the settlement is not approved, the plaintiffs may elect to g o forward with their appeal and no opinion is expressed regarding the likely outcome or financial impact of such an appeal on any fund.

On or about January 11, 2005, a putative class action lawsuit was filed in federal district court in Massachusetts against the Trust and its trustees, along with Columbia Management Advisors, LLC, the sub-administrator of the Wanger Advisors Funds and the Columbia Acorn Funds. The plaintiffs allege that the defendants failed to submit Proof of Claims in connection with settlements of securities class action lawsuits filed against companies in which the Columbia Acorn Funds held positions. The complaint seeks compensatory and punitive damages, and the disgorgement of all fees paid to Columbia Management Advisors, LLC. Plaintiffs have voluntarily dismissed the Trust and its independent trustees.

The Trust and CWAM intend to defend these suits vigorously.

As a result of these matters or any adverse publicity or other developments resulting from them, there may be increased redemptions or reduced sales of Fund shares, which could increase transaction costs or operating expenses, or have other adverse consequences for the Fund.

However, based on currently available information, the Trust believes that the likelihood that these lawsuits will have a material adverse impact on any fund is remote, and CWAM believes that the lawsuits are not likely to materially affect its ability to provide investment management services to the Fund.

22

Other Investment Strategies and Risks

The Fund's principal investment strategies and associated risks are described under "The Fund — Principal Investment Strategies" and "The Fund — Principal Investment Risks." This section describes other investments the Fund may make and the risks associated with them. In seeking to achieve its investment goal, the Fund may invest in various types of securities and engage in various investment techniques, which are not the principal focus of the Fund and therefore are not described in this prospectus. These types of securities and investment practices and their associated risks are identified and discussed in the Fund's SAI, which you may obtain free of charge (see back cover). The adviser may elect not to buy any of these securities or use any of these techniques. The Fund may not always achieve its investment goal. Except as otherwise noted, approval by the Fund's shareholders is not required to modify or change the F und's investment strategies.

THE INFORMATION EDGE

The Fund generally invests in entrepreneurially managed smaller- and mid-sized and larger companies that it believes are not as well known by financial analysts as the largest companies and whose position in a niche creates the opportunity for superior earnings-growth potential. CWAM may identify what it believes are important economic, social or technological trends (for example, the growth of outsourcing as a business strategy, or the productivity gains from the increasing use of technology) and try to identify companies it thinks will benefit from these trends.

In making investments for the Fund, CWAM relies primarily on independent, internally generated research to uncover companies that may be less well known than the more popular names. To find these companies, CWAM compares growth potential, financial strength and fundamental value among companies.

Growth Potential	Financial Strength	Fundamental Value
• superior technology • innovative marketing • managerial skill • market niche • good earnings prospects • strong demand for product	• low debt • adequate working capital • conservative accounting practices • adequate profit margin	• reasonable stock price relative to growth potential and financial strength • valuable assets
The realization of this growth potential would likely produce superior performance that is sustainable over time.	A strong balance sheet gives management greater flexibility to pursue strategic objectives and is important to maintaining a competitive advantage.	Once CWAM uncovers an attractive company, it identifies a price that it believes would also make the stock a good value.

LONG-TERM INVESTING

CWAM's analysts continually screen companies and make contact with more than 1,000 companies around the globe each year. To accomplish this, CWAM analysts often talk directly to top management, vendors, suppliers and competitors.

In managing the Fund, CWAM tries to maintain lower taxes and transaction costs by investing with a long-term time horizon (at least two to five years). However, securities purchased on a long-term basis may be sold within 12 months after purchase due to changes in the circumstances of a particular company or industry, or changes in general market or economic conditions.

23

Other Investment Strategies and Risks

DERIVATIVE STRATEGIES

The Fund may enter into a number of derivative strategies, including those that employ futures, options, straddles or similar transactions, to gain or reduce exposure to particular securities or markets. These strategies, commonly referred to as derivatives, involve the use of financial instruments whose values depend on, or are derived from, the value of an underlying security, index or currency. The Fund may use these strategies to adjust the Fund's sensitivity to changes in interest rates, or for other hedging purposes (i.e., attempting to offset a potential loss in one position by establishing an interest in an opposite position). Derivative strategies involve the risk that they may exaggerate a loss, potentially losing more money than the actual cost of the underlying security, or limit a potential gain. Also, with some derivative strategies there is a risk that the other party to the transaction may fail to honor its contr act terms, causing a loss to the Fund or that the Fund may not be able to find a suitable derivative transaction counterparty, and thus may be unable to invest in derivatives altogether.

TEMPORARY DEFENSIVE STRATEGIES

At times, CWAM may determine that adverse market conditions make it desirable to temporarily suspend the Fund's normal investment activities. During such times, the Fund may, but is not required to, invest in cash or high-quality, short-term debt securities, without limit. Taking a temporary defensive position may prevent the Fund from achieving its investment goal.

24

Financial Highlights

The financial highlights table is intended to help you understand the Fund's financial performance. Information is shown for the Fund's last five fiscal years, which run from January 1 to December 31. Certain information in the table reflects the financial results for a single Class A, B, or C share. The total returns in the table represent the return that you would have earned (or lost) on an investment in the Fund (assuming reinvestment of all dividends and distributions). This information has been derived from the Fund's financial statements, which have been audited for the years ended December 31, 2004, 2005 and 2006 by PricewaterhouseCoopers LLP, an independent registered public accounting firm, whose report, along with the Fund's financial statements, is included in the Fund's annual report. The information for the years ended December 31, 2002 and 2003 is included in the Fund's financial statements that have been audited by another independent registered public accounting firm, whose report expressed an unqualified opinion on those financial statements and highlights. You can request a free annual report containing those financial statements by calling 1-800-345-6611.

Columbia Acorn Select

	Year Ended December 31,
	2006			2005			2004			2003			2002
	Class A			Class A			Class A			Class A			Class A
Net asset value — Beginning of period ($)		22.47			20.83			18.01			13.93			15.17
Income from Investment Operations ($):
Net investment loss(a)		(0.13	)		(0.09	)		(0.16	)		(0.20)			(0.16	)
Net realized and unrealized gain (loss)		4.45			2.32			3.42			4.37			(1.08	)
Total from Investment Operations		4.32			2.23			3.26			4.17			(1.24	)
Less Distributions Declared to Shareholders ($):
From net investment income		(0.02	)		—			—			—			—
From net realized gains		(0.59	)		(0.59	)		(0.44	)		(0.09	)		—
Total Distributions Declared to Shareholders		(0.61	)		(0.59	)		(0.44	)		(0.09	)		—
Net asset value — End of period ($)		26.18			22.47			20.83			18.01			13.93
Total Return (%)(b)		19.32	(c)		10.78	(c)		18.16	(c)		29.95			(8.17	)(c)
Ratios to Average Net Assets/Supplemental Data (%):
Expenses(d)		1.24			1.26			1.47			1.63			1.70
Net investment loss		(0.54	)		(0.42	)(d)		(0.86	)(d)		(1.15	)(d)		(1.11	)(d)
Waiver/reimbursement		0.03			0.03			0.02			—			0.10
Portfolio turnover rate (%)		21			19			34			16			40
Net assets at end of period (000's) ($)		940,857			744,178			515,842			264,679			31,742

(a)  Per share data was calculated using average shares outstanding during the period.

(b)  Total return at net asset value assuming all distributions reinvested and no initial sales charge or contingent deferred sales charge.

(c)  Had the investment adviser and/or transfer agent not waived and/or reimbursed a portion of expenses, total return would have been reduced.

(d)  The benefits derived from custody fees paid indirectly had no impact.

25

Financial Highlights

Columbia Acorn Select

	Year Ended December 31,
	2006			2005			2004			2003			2002
	Class B			Class B			Class B			Class B			Class B
Net asset value — Beginning of period ($)		21.71			20.23			17.64			13.73			15.05
Income from Investment Operations ($):
Net investment loss(a)		(0.28	)		(0.23	)		(0.31	)		(0.29)			(0.25	)
Net realized and unrealized gain (loss)		4.29			2.24			3.34			4.29			(1.07)
Total from Investment Operations		4.01			2.01			3.03			4.00			(1.32	)
Less Distributions Declared to Shareholders ($):
From net realized gains		(0.59	)		(0.53	)		(0.44	)		(0.09)			—
Total Distributions Declared to Shareholders		(0.59	)		(0.53	)		(0.44	)		(0.09	)		—
Net asset value — End of period ($)		25.13			21.71			20.23			17.64			13.73
Total Return (%)(b)		18.54	(c)		10.01	(c)		17.24	(c)		29.14			(8.77)(c)
Ratios to Average Net Assets/Supplemental Data (%):
Expenses(d)		1.91			1.99			2.26			2.28			2.35
Net investment loss		(1.21	)		(1.15	)(d)		(1.65	)(d)		(1.80)(d)			(1.76	)(d)
Waiver/reimbursement		0.03			0.03			0.02			—			0.10
Portfolio turnover rate (%)		21			19			34			16			40
Net assets at end of period (000's) ($)		214,260			206,441			185,545			118,064			33,106

(a)  Per share data was calculated using average shares outstanding during the period.

(b)  Total return at net asset value assuming all distributions reinvested and no initial sales charge or contingent deferred sales charge.

(c)  Had the investment adviser and/or transfer agent not waived and/or reimbursed a portion of expenses, total return would have been reduced.

(d)  The benefits derived from custody fees paid indirectly had no impact.

26

Financial Highlights

Columbia Acorn Select

	Year Ended December 31,
	2006			2005			2004			2003			2002
	Class C			Class C			Class C			Class C			Class C
Net asset value — Beginning of period ($)		21.69			20.23			17.64			13.73			15.05
Income from Investment Operations ($):
Net investment loss(a)		(0.31	)		(0.25	)		(0.30	)		(0.30	)		(0.25	)
Net realized and unrealized gain (loss)		4.28			2.24			3.33			4.30			(1.07	)
Total from Investment Operations		3.97			1.99			3.03			4.00			(1.32)
Less Distributions Declared to Shareholders ($):
From net realized gains		(0.59	)		(0.53	)		(0.44	)		(0.09	)		—
Total Distributions Declared to Shareholders		(0.59	)		(0.53	)		(0.44	)		(0.09	)		—
Net asset value — End of period ($)		25.07			21.69			20.23			17.64			13.73
Total Return(%)(b)		18.37	(c)		9.91	(c)		17.24	(c)		29.14			(8.77	)(c)
Ratios to Average Net Assets/Supplemental Data (%):
Expenses(d)		2.04			2.08			2.25			2.28			2.35
Net investment loss		(1.34	)		(1.24	)(d)		(1.64	)(d)		(1.80	)(d)		(1.76	)(d)
Waiver/reimbursement		0.03			0.03			0.02			—			0.10
Portfolio turnover rate (%)		21			19			34			16			40
Net assets at end of period (000's) ($)		173,152			149,160			110,435			64,212			10,919

(a)  Per share data was calculated using average shares outstanding during the period.

(b)  Total return at net asset value assuming all distributions reinvested and no initial sales charge or contingent deferred sales charge.

(c)  Had the investment adviser and/or transfer agent not waived and/or reimbursed a portion of expenses, total return would have
been reduced.

(d)  The benefits derived from custody fees paid indirectly had no impact.

27

Appendix

Hypothetical Investment and Expense Information

The Fund is required to disclose the following supplemental hypothetical investment information, which provides additional information about the effect of the expenses paid by the Fund, including investment advisory fees and other Fund costs, on the Fund's returns over a 10-year period. The tables show the estimated expenses that would be charged on a hypothetical investment of $10,000 in each class of the Fund assuming a 5% return each year, the cumulative return after fees and expenses, and the hypothetical year-end balance after fees and expenses. The tables also assume that all dividends and distributions are reinvested and that Class B shares convert to Class A shares after eight years. The annual expense ratios used for the Fund, which are the same as those stated in the Annual Fund Operating Expenses table, are presented in the charts, and are net of any contractual fee waivers or expense reimbursements for the period of the contractual commitment. Your actual costs may be higher or lower. The tables shown below reflect the maximum initial sales charge for Class A shares but do not reflect any contingent deferred sales charges which may be payable on redemption. If contingent deferred sales charges were reflected, the "Hypothetical Year-End Balance After Fees and Expenses" amounts shown would be lower and the "Annual Fees and Expenses" amounts shown would be higher. As noted previously, the Fund's minimum investment for initial purchases or exchanges is $50,000.

Columbia Acorn Select — Class A Shares

Maximum Sales Charge 5.75%					Initial Hypothetical Investment Amount $10,000.00						Assumed Rate of Return 5%
Year		Cumulative Return Before Fees & Expenses			Annual Expense Ratio			Cumulative Return After Fees & Expenses			Hypothetical Year-End Balance After Fees & Expenses		Annual Fees & Expenses(1)
	1		5.00	%		1.27	%		-2.23	%(2)	$	9,776.55	$	696.93
	2		10.25	%		1.27	%		1.41	%	$	10,141.22	$	126.48
	3		15.76	%		1.27	%		5.19	%	$	10,519.49	$	131.20
	4		21.55	%		1.27	%		9.12	%	$	10,911.86	$	136.09
	5		27.63	%		1.27	%		13.19	%	$	11,318.87	$	141.17
	6		34.01	%		1.27	%		17.41	%	$	11,741.07	$	146.43
	7		40.71	%		1.27	%		21.79	%	$	12,179.01	$	151.89
	8		47.75	%		1.27	%		26.33	%	$	12,633.29	$	157.56
	9		55.13	%		1.27	%		31.05	%	$	13,104.51	$	163.44
	10		62.89	%		1.27	%		35.93	%	$	13,593.31	$	169.53
Total Gain After Fees and Expenses											$	3,593.31
Total Annual Fees and Expenses													$	2,020.72

(1)   Annual Fees and Expenses are calculated based on the average between the beginning and ending balance for each year. All information is calculated on an annual compounding basis.

(2)   Reflects deduction of the maximum initial sales charge.

28

Appendix

Columbia Acorn Select — Class B Shares

Maximum Sales Charge 0.00%					Initial Hypothetical Investment Amount $10,000.00						Assumed Rate of Return 5%
Year		Cumulative Return Before Fees & Expenses			Annual Expense Ratio			Cumulative Return After Fees & Expenses			Hypothetical Year-End Balance After Fees & Expenses		Annual Fees & Expenses(1)
	1		5.00	%		1.88	%		3.12	%	$	10,312.00	$	190.93
	2		10.25	%		1.88	%		6.34	%	$	10,633.73	$	196.89
	3		15.76	%		1.88	%		9.66	%	$	10,965.51	$	203.03
	4		21.55	%		1.88	%		13.08	%	$	11,307.63	$	209.37
	5		27.63	%		1.88	%		16.60	%	$	11,660.43	$	215.90
	6		34.01	%		1.88	%		20.24	%	$	12,024.23	$	222.64
	7		40.71	%		1.88	%		23.99	%	$	12,399.39	$	229.58
	8		47.75	%		1.88	%		27.86	%	$	12,786.25	$	236.75
	9		55.13	%		1.27	%		32.63	%	$	13,263.18	$	165.41
	10		62.89	%		1.27	%		37.58	%	$	13,757.89	$	171.58
Total Gain After Fees and Expenses											$	3,757.89
Total Annual Fees and Expenses													$	2,042.08

(1)   Annual Fees and Expenses are calculated based on the average between the beginning and ending balance for each year. All information is calculated on an annual compounding basis.

29

Appendix

Columbia Acorn Select — Class C Shares

Maximum Sales Charge 0.00%					Initial Hypothetical Investment Amount $10,000.00						Assumed Rate of Return 5%
Year		Cumulative Return Before Fees & Expenses			Annual Expense Ratio			Cumulative Return After Fees & Expenses			Hypothetical Year-End Balance After Fees & Expenses		Annual Fees & Expenses(1)
	1		5.00	%		2.08	%		2.92	%	$	10,292.00	$	211.04
	2		10.25	%		2.08	%		5.93	%	$	10,592.53	$	217.20
	3		15.76	%		2.08	%		9.02	%	$	10,901.83	$	223.54
	4		21.55	%		2.08	%		12.20	%	$	11,220.16	$	230.07
	5		27.63	%		2.08	%		15.48	%	$	11,547.79	$	236.79
	6		34.01	%		2.08	%		18.85	%	$	11,884.99	$	243.70
	7		40.71	%		2.08	%		22.32	%	$	12,232.03	$	250.82
	8		47.75	%		2.08	%		25.89	%	$	12,589.20	$	258.14
	9		55.13	%		2.08	%		29.57	%	$	12,956.81	$	265.68
	10		62.89	%		2.08	%		33.35	%	$	13,335.15	$	273.44
Total Gain After Fees and Expenses											$	3,335.15
Total Annual Fees and Expenses													$	2,410.42

(1)  Annual Fees and Expenses are calculated based on the average between the beginning and ending balance for each year. All information is calculated on an annual compounding basis.

30

Notes

31

FOR MORE INFORMATION

Additional information about the Fund's investments is available in the Fund's semiannual and annual reports to shareholders. The annual report contains a discussion of the market conditions and investment strategies that significantly affected the Fund's performance during its last fiscal year.

You may wish to read the SAI for more information on the Fund and the securities in which it invests. The SAI is incorporated into this prospectus by reference, which means that it is considered to be part of this prospectus.

You can get free copies of annual and semiannual reports and the SAI, request other information and discuss your questions about the Fund by visiting www.columbiafunds.com or by writing or calling the Fund's transfer agent at:

Columbia Management Services, Inc.
P.O. Box 8081
Boston, MA 02266-8081
1-800-345-6611

Text-only versions of all Fund documents can be viewed online or downloaded from the EDGAR database on the Securities and Exchange Commission internet site at www.sec.gov.

You can review and copy information about the Fund, including the SAI, by visiting the following location, and you can obtain copies upon payment of a duplicating fee, by electronic request at the e-mail address publicinfo@sec.gov or by writing the:

Public Reference Room
Securities and Exchange Commission
Washington, DC 20549-0102

Information on the operation of the Public Reference Room may be obtained by calling 1-202-942-8090.

Investment Company Act file number:
Columbia Acorn Trust: 811-01829
•  Columbia Acorn Select

©2007 Columbia Management Distributors, Inc.
One Financial Center, Boston, MA 02111-2621
800.426.3750 www.columbiafunds.com

INT-36/130216-0507

Columbia^SM

Acorn Select^SM  Prospectus, May 1, 2007

Class Z Shares

Advised by Columbia Wanger Asset Management, L.P.

TABLE OF CONTENTS

THE FUND	2
Investment Goal	2
Principal Investment Strategies	2
Principal Investment Risks	2
Portfolio Holdings Disclosure	3
Performance History	4
Your Expenses	5
YOUR ACCOUNT	7
How to Buy Shares	7
Eligible Investors	8
Sales Charges (Commissions)	10
How to Exchange Shares	10
How to Sell Shares	11
Fund Policy on Trading of Fund Shares	12
Financial Intermediary Payments	13
Other Information About Your Account	14
BOARD OF TRUSTEES	17
MANAGING THE FUND	17
Investment Adviser	17
Portfolio Manager	17
Legal Proceedings	18
OTHER INVESTMENT STRATEGIES AND RISKS	19
The Information Edge	20
Long-Term Investing	20
Derivative Strategies	21
Temporary Defensive Strategies	21
FINANCIAL HIGHLIGHTS	22
APPENDIX	23

Only eligible investors may purchase Class Z shares. See "Your Account — Eligible Investors" for more information.

Although these securities have been registered with the Securities and Exchange Commission, the Commission has not approved or disapproved any shares offered in this prospectus or determined whether this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Acorn Select is a trademark owned and registered by Columbia Acorn Trust, Columbia, Columbia Management^® and Columbia Management Services, Inc. are service marks owned and/or registered by Bank of America

The Fund

INVESTMENT GOAL

Columbia Acorn Select (Acorn Select^SM) seeks long-term growth of capital.

PRINCIPAL INVESTMENT STRATEGIES

Acorn Select generally invests in the stocks of U.S. companies. The Fund is a non-diversified fund that takes advantage of its adviser's research and stock-picking capabilities to invest in a limited number of companies (between 20-40) with market capitalizations under $20 billion at the time of initial purchase, offering the potential to provide above-average growth over time.

Acorn Select believes that companies within this capitalization range, which are not as well known by financial analysts as the largest companies, may offer higher return potential than the stocks of companies with capitalizations above $20 billion.

Acorn Select typically looks for companies with:

•  A strong business franchise that offers growth potential.

•  Products and services that give the company a competitive advantage.

•  A stock price the Fund's investment adviser believes is reasonable relative to the assets and earning power of the company.

Although Acorn Select does not buy securities with a short-term view, there is no restriction on the length of time the Fund must hold a security. To the extent the Fund buys and sells securities frequently, its transaction costs will be higher (which may adversely affect the Fund's performance) and it may realize additional capital gains.

Acorn Select invests the majority of its assets in U.S. companies, but also may invest up to 25% of its assets, valued at the time of investment, in companies outside the United States in developed markets (for example, Japan, Canada and the United Kingdom) and emerging markets (for example, Mexico, Brazil and Korea).

Additional strategies that are not principal investment strategies and the risks associated with them are described later in this prospectus under "Other Investment Strategies and Risks."

PRINCIPAL INVESTMENT RISKS

The principal risks of investing in the Fund are described below. There are many circumstances (including additional risks that are not described here) that could prevent the Fund from achieving its investment goal. You may lose money by investing in the Fund.

Management risk means that the adviser's investment decisions might produce losses or cause the Fund to underperform when compared to other funds with a similar investment goal. Market risk means that security prices in a market, sector or industry may fall, reducing the value of your investment. Because of management and market risk, there is no guarantee that the Fund will achieve its investment goal or perform favorably among comparable funds.

Since the Fund purchases equity securities, it is subject to equity risk. This is the risk that stock prices will fall over short or extended periods of time. Although the stock market historically has outperformed other asset classes over the long term, the stock market tends to move in cycles. Individual stock prices may fluctuate drastically from day-to-day and may underperform other asset classes over an extended period of time.

2

The Fund

Individual companies may report poor results or be negatively affected by industry and/or economic trends and developments. The prices of securities issued by such companies may suffer a decline in response. These price movements may result from factors affecting individual companies, industries or the securities market as a whole.

Because the Fund invests in stocks, the price of its shares — its net asset value (NAV) per share — fluctuates daily in response to changes in market value of stocks.

Sector risk is inherent in the Fund's investment strategy. Companies that are in different but closely related industries are sometimes described as being in the same broad economic sector. The values of stocks of different companies in a market sector may be similarly affected by particular economic or market events. Although the Fund does not intend to focus on any particular sector, at times the Fund may have a large portion of its assets invested in a particular sector.

Small- or mid-cap companies may be more susceptible to market downturns, and their prices could be more volatile. These companies are more likely than larger companies to have limited product lines, operating histories, markets or financial resources. They may depend heavily on a small management team and may trade less frequently, may trade in smaller volumes and may fluctuate more sharply in price than stocks of larger companies. In addition, such companies may not be widely followed by the investment community, which can lower the demand for their stocks.

Foreign securities are subject to special risks. Foreign markets may be extremely volatile. Fluctuations in currency exchange rates will impact the dollar value of foreign securities denominated in foreign currencies and U.S. dollars, without a change in the intrinsic value of those securities. The liquidity of foreign securities may be more limited than that of domestic securities, which means that the Fund may, at times, be unable to sell foreign securities at desirable prices. Brokerage commissions, custodial fees and other fees are generally higher for foreign investments. In addition, foreign governments may impose withholding taxes that would reduce the amount of income and capital gains available to distribute to shareholders. Other risks include possible delays in the settlement of transactions or in the notification of income; less publicly a vailable information about companies; the impact of political, social or diplomatic events; possible seizure, expropriation or nationalization of the company or its assets; and possible imposition of currency exchange controls.

Investments in emerging markets are subject to additional risk. The risks of foreign investments are typically increased in less developed countries, which are sometimes referred to as emerging markets. For example, political and economic structures in these countries may be new and developing rapidly, which may cause instability. These countries are also more likely to experience high levels of inflation, deflation or currency devaluations, which could hurt their economies and securities markets.

As a non-diversified mutual fund, the Fund is allowed to invest a greater percentage of its total assets in the securities of fewer issuers than a "diversified" fund. The Fund may, therefore, have a greater risk of loss from a few issuers than a similar fund that invests more broadly.

An investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PORTFOLIO HOLDINGS DISCLOSURE

A description of the Fund's policies and procedures with respect to the disclosure of its portfolio securities is available in the Fund's Statement of Additional Information (SAI), which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611.

3

The Fund

The Fund posts its complete portfolio holdings at as of month-end www.columbiafunds.com approximately 30-40 calendar days after such month-end. Additionally, the Fund discloses its top 15 month-end portfolio holdings at www.columbiafunds.com on or about 15 calendar days following such month-end.

Once posted, the above information will remain available on the website until at least the date on which the Fund files a Form N-CSR or Form N-Q for the period that includes the date as of which the information is current.

PERFORMANCE HISTORY

The bar chart below shows the Fund's calendar-year total returns (before taxes) for its Class Z shares. The performance table following the bar chart shows how the Fund's average annual total returns for Class Z shares compare with a broad measure of market performance for one year, five years and the life of the share class. The chart and table are intended to illustrate some of the risks of investing in the Fund by showing changes in the Fund's performance from year to year. All returns include the reinvestment of dividends and distributions. Performance results include the effect of expense reduction arrangements. If these arrangements had not been in place, then performance would have been lower. Any expense reduction arrangements may be discontinued at any time. As with all mutual funds, past performance (before and after taxes) does not predict the Fund's future performance.

UNDERSTANDING PERFORMANCE

Calendar Year Total Returns show the Fund's Class Z share performance for each completed calendar year since the Fund commenced operations. Those returns include the effects of Fund expenses.

Average Annual Total Returns are a measure of the Fund's Class Z average performance over the past one year, five years and life of the share class. They include the effects of Fund expenses.

The Fund's returns are compared to the Standard & Poor's MidCap 400 Index (S&P MidCap 400 Index). The S&P MidCap 400 Index is an unmanaged, market value-weighted index of 400 mid-cap U.S. companies. Unlike the Fund, an index is not an investment, does not incur fees, expenses or taxes, and is not professionally managed.

Calendar Year Total Returns (Class Z)

For the periods shown in bar chart:
Best quarter: 4th quarter 2001, +17.57%
Worst quarter: 3rd quarter 2001, -11.34%

4

The Fund

After tax returns are calculated using the highest historical individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on each investor's own tax situation and may differ from those shown. After-tax returns may not be relevant to investors who hold Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Average Annual Total Returns — for periods ended December 31, 2006

Share Class	1 Year		5 Years		Life of the Share Class(1)
Class Z (%)
Return Before Taxes		19.68		13.67		15.30
Return After Taxes on Distributions		19.11		13.36		14.76
Return After Taxes on Distributions and Sale of Fund Shares		13.21		11.93		13.46
Index
S&P MidCap 400 Index (%)		10.32		10.89		11.94	(2)

(1)  The inception date for Class Z shares is November 23, 1998.

(2)  Performance information is from November 23, 1998.

YOUR EXPENSES

Expenses are one of several factors to consider before you invest in a mutual fund. The tables below describe the fees and expenses you may pay when you buy, hold and sell shares of the Fund.

UNDERSTANDING EXPENSES

Annual Fund Operating Expenses are paid by the Fund. They include management and administration fees and other expenses that generally include, but are not limited to, transfer agency, custody, and legal fees as well as costs related to state registration and printing of Fund documents. The specific fees and expenses that make up the Fund's other expenses will vary from time to time and may include fees or expenses not described here. The Fund will likely incur portfolio transaction costs that are in addition to the total annual fund operating expenses disclosed in the fee table. These transaction costs are made up of all costs that are associated with trading securities for the Fund's portfolio and include, but are not limited to, brokerage commissions and market spreads, as well as potential changes to the price of a security due to the Fund's effor ts to purchase or sell it. While certain elements of transaction costs are readily identifiable and quantifiable, other elements that can make up a significant amount of the Fund's transaction costs are not. Higher transaction costs reduce the Fund's returns.

Shareholder Fees (commissions paid directly from your investment)

Maximum sales charge (load) on purchases (%) (as a percentage of offering price)	None
Maximum deferred sales charge (load) on redemptions (%) (as a percentage of the lesser of purchase price or redemption price)	None
Redemption fee (%) (as a percentage of amount redeemed, if applicable)	None(1)

(1)  There is a $7.50 charge for wiring sale proceeds to your bank.

5

The Fund

Annual Fund Operating Expenses (deducted directly from Fund assets)

Management fees(1) (%)	0.82
Distribution and service (12b-1) fees (%)	None
Other expenses(2) (%)	0.16
Total annual fund operating expenses(3) (%)	0.98

(1)  The Fund pays an investment advisory fee of 0.82%. The Fund's adviser has implemented a breakpoint schedule for the Fund's investment advisory fees. The investment advisory fees charged to the Fund will decline as Fund assets grow and will continue to be based on a percentage of the Fund's average daily assets. The breakpoint schedule for the Fund is as follows: 0.85% for assets up to $700 million; 0.80% for assets in excess of $700 million and up to $2 billion; 0.75% for assets in excess of $2 billion and up to $3 billion; and 0.70% for assets in excess of $3 billion. In addition to the management fee, the Fund and the other funds of Columbia Acorn Trust (the "Trust") pay the adviser an administrative fee based on the average daily aggregate net assets of the Trust at the following annual rates: 0.05% of net assets up to $8 billion; 0.04% of the next $8 billion; and 0.03% of net assets in excess of $16 billion. B ased on the Trust's average daily net assets as of December 31, 2006, the administrative fee would be at a rate of 0.04% and is included in "Other expenses."

(2)  "Other expenses" have been restated to reflect contractual changes to the transfer agency fees paid by the Fund.

(3)  The Fund's adviser has voluntarily agreed to reimburse the Fund for any ordinary operating expenses (exclusive of distribution and service fees, interest, taxes and extraordinary expenses, if any) exceeding the annual rate of 1.35% of the average daily net assets for Class Z shares. This arrangement may be modified or terminated by either the Fund or its adviser on 30 days notice.

Example Expenses help you compare the cost of investing in the Fund to the cost of investing in other mutual funds. The table does not take into account any expense reduction arrangements discussed in the footnotes to the Annual Fund Operating Expenses table. It uses the following hypothetical conditions:

•  $10,000 initial investment^†

•  5% total return for each year

•  Fund operating expenses remain the same

•  Reinvestment of all dividends and distributions

†  For example only, since the minimum initial investment in the Fund is $50,000, subject to certain exceptions  described in the section "Eligible Investors" on page 8.

Example Expenses for a $10,000 investment (your actual costs may be higher or lower)

1 Year		3 Years		5 Years		10 Years
$	100	$	312	$	542	$	1,201

See the Appendix for additional hypothetical investment and expense information.

6

Your Account

HOW TO BUY SHARES

If you are an eligible investor (described on page 8), when the Fund receives your purchase request in "good form," your shares will be bought at the next calculated price. "Good form" means that the Fund's transfer agent has all information and documentation it deems necessary to effect your order. For example "good form" may mean that you have properly placed your order with Columbia Management Services, Inc. or your financial advisor or the Fund's transfer agent has received your completed application, including all necessary signatures. The Fund reserves the right to refuse a purchase order for any reason, including if the Fund believes that doing so would be in the best interest of the Fund and its shareholders. The USA PATRIOT Act may require us to obtain certain personal information from you that we will use to verify your identity. If you do not provide the information, we may not be able to open your account. If we are unable to verify your customer information, we reserve the right to close your account or take such other steps as we deem reasonable.

You or your financial advisor may acquire shares of the Fund for your account by exchanging shares you own in a different fund distributed by Columbia Management Distributors, Inc. for shares of the same class or Class A of the Fund at no additional cost. To exchange by telephone, call 1-800-422-3737. Please see "How to Exchange Shares" for more information.

Outlined below are the various options for buying shares:

Method	Instructions
Through your financial advisor	Your financial advisor can help you establish your account and buy Fund shares on your behalf. To receive the current trading day's price, your financial advisor must receive your request prior to the close of regular trading on the New York Stock Exchange (NYSE), usually 4:00 p.m. Eastern time. Your financial advisor may charge you fees for executing the purchase for you.
By check (new account)	For new accounts, send a completed application and check made payable to the Fund to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By check (existing account)	For existing accounts, fill out and return the additional investment stub included in your account statement, or send a letter of instruction including the Fund name and account number with a check made payable to the Fund and mailed to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By exchange	You may acquire Fund shares for your account by exchanging shares you own in a different fund distributed by Columbia Management Distributors, Inc. for shares of the same class or Class A shares of the Fund at no additional cost. To exchange by telephone, call 1-800-422-3737. Please see "How to Exchange Shares" for more information.
By wire	You may purchase Fund shares by wiring money from your bank account to your Fund account. To wire funds to your Fund account, call 1-800-422-3737 for wiring instructions.
By electronic funds transfer	You may purchase Fund shares by electronically transferring money from your bank account to your Fund account by calling 1-800-422-3737. An electronic fund transfer may take up to two business days to settle and must be considered in "good form." You must set up this feature prior to your telephone request. Be sure to complete the appropriate section of the application for this feature.
Automatic investment plan	You may make monthly or quarterly investments ($50 minimum) automatically from your bank account to your Fund account. You may select a pre-authorized amount to be sent via electronic funds transfer. Be sure to complete the appropriate section of the application for this feature.
Automated dollar cost averaging	You may purchase Fund shares for your account by exchanging $100 or more each month from another fund for shares of the same class of the Fund at no additional cost. Exchanges will continue so long as your fund balance is sufficient to complete the transfers. You may terminate your program or change the amount of the exchange (subject to the $100 minimum) by calling 1-800-345-6611. Be sure to complete the appropriate section of the account application for this feature.
By dividend diversification	You may automatically invest dividends distributed by another fund into the same class of shares of the Fund at no additional sales charge. There may be an additional sales charge if automatically investing dividends from a money market fund. To invest your dividends in the Fund, call 1-800-345-6611.

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Method	Instructions
Through the internet	You may purchase Fund shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet purchases. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

ELIGIBLE INVESTORS

Only certain eligible investor may purchase Class Z shares of the Fund (Eligible Investor), directly or by exchange. Please read the following section for a more detailed description of the eligibility requirements. The Eligible Investors described below are subject to different minimum initial investment requirements.

Eligibility for certain waivers, exemptions or share classes by new or existing investors may not be readily available or accessible through all intermediaries or all types of accounts offered by a broker-dealer, bank, third-party administrator or other financial institution (each commonly referred to as an "intermediary"). Accessibility of these waivers through a particular intermediary also may change at any time. If you believe you are eligible to purchase shares under a specific exemption, but are not permitted by your intermediary to do so, please contact your intermediary. You may be asked to provide information, including account statements and other records, regarding your eligibility.

Eligible Investors and their applicable investment minimums are as follows:

No minimum initial investment

•  Any trustee or director (or family member of a trustee or director) of Columbia Acorn Trust;

•  An employee (or family member of an employee) of Columbia Wanger Asset Management, L.P.; or

•  Any group retirement plan, holding Fund shares in an omnibus manner, for which an intermediary or other entity provides services and is not compensated by the Funds for those services, other than payments for shareholder servicing or sub-accounting performed in place of the transfer agent.

$50,000 minimum initial investment

•  Any individual retirement account of an Eligible Investor;

•  Any group retirement plan, not holding Fund shares in an omnibus manner, for which an intermediary or other entity provides services and is not compensated by the Fund for those services, other than compensation for shareholder servicing or sub-accounting performed in place of the transfer agent;

•  Any shareholder (as well as any family member of a shareholder or person listed on an account registration for any account of the shareholder) of a fund distributed by Columbia Management Distributors, Inc. (CMD) (i) who holds Class Z shares; (ii) who holds shares issued upon conversion of Primary A shares held prior to August 22, 2005; (iii) who holds Class A shares that were obtained by exchange of Class Z shares; or (iv) who holds no-load shares issued upon the merger of a fund distributed by CMD;

•  Any trustee or director (or family member of a trustee or director) of any fund distributed by CMD (other than the Columbia Acorn Funds);

•  Any employee (or family member of an employee) of Bank of America Corporation or a subsidiary (other than Columbia Wanger Asset Management L.P.);

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•  Any investor participating in an account offered by an intermediary or other entity that provides services to such an account, is paid an asset-based fee by the investor and is not compensated by the Funds for those services, other than payments for shareholder servicing or sub-accounting performed in place of the Fund's transfer agent (each investor purchasing through an intermediary must independently satisfy the $50,000 minimum investment requirement);

•  Any client of Bank of America Corporation or a subsidiary purchasing through an asset management company, trust, fiduciary, retirement plan administration or similar arrangement with Bank of America Corporation or the subsidiary;

•  Any person investing all or part of the proceeds of a distribution, rollover or transfer of assets into a Columbia Management Individual Retirement Account from any deferred compensation plan which was a shareholder of any of the funds of Columbia Acorn Trust (formerly named Liberty Acorn Trust) on September 29, 2000, in which the investor was a participant and through which the investor invested in one or more of the funds of Columbia Acorn Trust immediately prior to the distribution, transferor rollover;

•  Any investor purchasing through a Columbia Management state tuition plan organized under Section 529 of the Internal Revenue Code;

•  Any institutional investor which is a corporation, partnership, trust, foundation, endowment, institution, government entity, or similar organization; which meets the respective qualifications for an accreditedinvestor, as defined under the Securities Act of 1933; or

•  Certain financial institutions and intermediaries, such as insurance companies, trust companies, banks, endowments, investment companies or foundations, purchasing shares for its own account, including Bank of America Corporation, its affiliates, or subsidiaries.

The investment minimum is applied at the class level. For group retirement plans, the investment minimum is determined based on the amount of the plan's investment rather than that of its individual participants. The Fund may establish exclusions from the investment minimum from time to time that it deems appropriate and consistent with the interests of shareholders. Please see the SAI for details on these exclusions.

The Fund reserves the right to change the criteria for eligible investors and the investment minimums. For accounts opened prior to August 5, 2005, minimum investment applies to accounts participating in the automatic investment plan; however, each investment requires a $50 minimum purchase. The Fund also reserves the right to refuse a purchase order for any reason, including if it believes that doing so would be in the best interest of the Fund and its shareholders. Finally, pursuant to the Trust's Agreement and Declaration of Trust, the Fund reserves the right to redeem your shares if your account falls below the minimum investment requirements.

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SALES CHARGES (COMMISSIONS)

Your purchases of Class Z shares are at net asset value, which is the value of a Class Z share excluding any sales charge. Class Z shares are not subject to an initial sales charge when purchased, or a contingent deferred sales charge when sold.

CHOOSING A SHARE CLASS

The Fund offers one class of shares in this prospectus — Class Z.

The Fund also offers three additional classes of shares — Class A, B and C shares are available through a separate prospectus. Each other share class has its own sales charge and expense structure.

Broker-dealers, investment advisers or financial planners selling mutual fund shares may offer their clients more than one class of shares in a fund with different pricing options. This allows you and your financial advisor to choose among different types of sales charges and different levels of ongoing operating expenses, depending on the investment programs your financial advisor offers. Investors should consider carefully any separate transactions and other fees charged by these programs in connection with investing in any available share class before selecting a share class.

Determining which share class is best for you depends on the dollar amount you are investing and the number of years for which you are willing to invest. Based on your personal situation, your financial advisor can help you decide which class of shares makes the most sense for you. In general, anyone who is eligible to purchase Class Z shares, which do not incur Rule 12b-1 fees or sales charges, should do so in preference over other classes.

If you purchase Class Z shares of the Fund through certain intermediaries, they may charge a fee for their services. They may also place limits on your ability to use services the Fund offers. There are no sales charges or limitations if you purchase shares directly from the Fund, except as described in this prospectus.

If an intermediary is an agent or designee of the Fund, orders are processed at the net asset value next calculated after the intermediary receives the order. The intermediary must segregate any orders it receives after the close of regular trading on the NYSE and transmit those orders separately for execution at the net asset value next determined.

HOW TO EXCHANGE SHARES

You may exchange your shares for Class Z or Class A (only if Class Z is not offered) shares of another fund distributed by CMD at net asset value. Unless your account is part of a tax-deferred retirement plan, an exchange is a taxable event, and you may realize a gain or a loss for tax purposes. The Fund may terminate your exchange privilege if the adviser determines that your exchange activity is likely to adversely impact its ability to manage the Fund. See "Fund Policy on Trading of Fund Shares" for the Fund's policy. To exchange by telephone, call 1-800-422-3737. Please have your account and taxpayer identification numbers available when calling.

You also may exchange your shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet exchanges. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

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HOW TO SELL SHARES

You may sell shares of the Fund on any regular business day that the NYSE is open.

When the Fund receives your sales request in "good form," shares will be sold at the next calculated net asset value. "Good form" means that the Fund's transfer agent has all information and documentation it deems necessary to effect your order. For example, when selling shares by letter of instruction, "good form" means (i) your letter has complete instructions, the proper signatures and Medallion Signature Guarantees, and (ii) any other required documents are attached. For additional documents required for sales by corporations, agents, fiduciaries, surviving joint owners and other legal entities, please call 1-800-422-3737. Retirement plan accounts have special requirements; please call 1-800-799-7526 for more information.

The Fund will generally send proceeds from the sale to you within seven days (usually on the next business day after your request is received in "good form"). However, if you purchased your shares by check, the Fund may delay sending the proceeds from the sale of your shares for up to 10 days after your purchase to protect against checks that are returned. No interest will be paid on uncashed redemption checks. Redemption proceeds may be paid in securities, rather than cash, under certain circumstances. For more information, see the paragraph "Non-Cash Redemptions" under the section "How to Sell Shares" in the SAI.

During any 90-day period for any one shareholder, the Fund is obligated to redeem shares solely in cash up to the lesser of $250,000 or 1% of the Fund's net assets. Redemptions in excess of these limits will normally be paid in cash, but may be paid wholly or partly by an in-kind distribution of securities.

Outlined below are the various options for selling shares:

Method	Instructions
Through your financial advisor	You may call your financial advisor to place your sell order. To receive the current trading day's price, your financial advisor must receive your request prior to the close of regular trading on the NYSE, usually 4:00 p.m. Eastern time. Your financial advisor may charge you fees for executing a redemption for you.
By exchange	You or your financial advisor may sell Fund shares by exchanging from the Fund into Class Z shares or Class A shares (only if Class Z is not offered) of another fund distributed by Columbia Management Distributors, Inc. at no additional cost. To exchange by telephone, call 1-800-422-3737.
By telephone	You or your financial advisor may sell Fund shares by telephone and request that a check be sent to your address of record by calling 1-800-422-3737, unless you have notified the Fund of an address change within the previous 30 days. The dollar limit for telephone sales is $100,000 in a 30-day period. You do not need to set up this feature in advance of your call. Certain restrictions apply to retirement accounts. For details, call 1-800-799-7526.
By mail	You may send a signed letter of instruction to the address below. In your letter of instruction, note the Fund's name, share class, account number, and the dollar value or number of shares you wish to sell. All account owners must sign the letter. Signatures must be guaranteed by either a bank, a member firm of a national stock exchange or another eligible guarantor that participates in the Medallion Signature Guarantee Program for amounts over $100,000 or for alternate payee or mailing instructions. Additional documentation is required for sales by corporations, agents, fiduciaries, surviving joint owners and individual retirement account owners. For details, call 1-800-345-6611. Mail your letter of instruction to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.

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Method	Instructions
By wire	You may sell Fund shares and request that the proceeds be wired to your bank. You must set up this feature prior to your request. Be sure to complete the appropriate section of the account application for this feature. Generally, the value of your redemption must be at least equal to $500 in order to have the sale proceeds wired to your bank. There is a $7.50 charge for wiring sale proceeds to your bank. (The transfer agent may waive this fee for omnibus and nominee accounts.) Your bank may charge additional fees for such wire transfer.
By systematic withdrawal plan	You may automatically sell a specified dollar amount or percentage of your account on a monthly, quarterly or semiannual basis and have the proceeds sent to you if your account balance is at least $5,000. The $5,000 minimum account balance requirement is waived for wrap accounts. All dividend and capital gains distributions must be reinvested. Be sure to complete the appropriate section of the account application for this feature.
By electronic funds transfer	You may sell Fund shares and request that the proceeds be electronically transferred to your bank. Proceeds may take up to two business days to be received by your bank. You must set up this feature prior to your request. Be sure to complete the appropriate section of the account application for this feature.
Through the internet	You may sell Fund shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet redemptions. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

FUND POLICY ON TRADING OF FUND SHARES

The interests of the Fund's long-term shareholders may be adversely affected by certain short-term trading activity by Fund shareholders. Such short-term trading activity, when excessive, has the potential to interfere with efficient portfolio management, generate transaction and other costs, dilute the value of Fund shares held by long-term shareholders and have other adverse effects on the Fund. This type of excessive short-term trading activity is referred to herein as "market timing." For purposes of this section "Columbia Funds" are the Columbia, Columbia Acorn Trust and Wanger Advisors Trust families of mutual funds. The Columbia Funds are not intended as vehicles for market timing. The Board of Trustees of the Fund has adopted the policies and procedures set forth below with respect to frequent trading of the Fund's shares.

The Fund, directly and through its agents, takes various steps designed to deter and curtail market timing. For example, if the Fund detects that any shareholder has conducted two "round trips" (as defined below) in the Fund in any 28-day period, except as noted below with respect to orders received through omnibus accounts, the Fund will reject the shareholder's future purchase orders, including exchange purchase orders, involving any Columbia fund (other than a money market fund). In addition, if the Fund determines that any person, group or account has engaged in any type of market timing activity (independent of the two-round-trip limit), the Fund may, in its discretion, reject future purchase orders by the person, group or account, including exchange purchase orders, involving the same or any other Columbia fund, and also retains the right to modify these market timing policies at any time without prior notice.

The rights of shareholders to redeem shares of the Fund are not affected by any of the limits mentioned above. However, certain funds (other than the Fund) impose a redemption fee on the proceeds of fund shares that are redeemed or exchanged within 60 days of their purchase.

For these purposes, a "round trip" is a purchase by any means into a Columbia fund followed by a redemption, of any amount, by any means out of the same Columbia fund. Under this definition, an exchange into the Fund followed by an exchange out of the Fund is treated as a single round trip. Also for these purposes, where known, accounts under common ownership or control generally will be counted together. Accounts maintained or managed by a common intermediary, such as an adviser, selling agent or trust department, generally will not be considered to be under common ownership or control.

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Purchases, redemptions and exchanges made through the Columbia Funds' Automatic Investment Plan, Systematic Withdrawal Plan or similar automated plans are not subject to the two-round-trip limit. Purchases, redemptions and exchanges made by Columbia Thermostat Fund are also not subject to the two round-trip limit. The two-round-trip limit may be modified for, or may not be applied to, accounts held by certain retirement plans to conform to plan limits, considerations relating to the Employee Retirement Income Security Act of 1974 or regulations of the Department of Labor, and for certain asset allocation or wrap programs.

The practices and policies described above are intended to deter and curtail market timing in the Fund. However, there can be no assurance that these policies, individually or collectively, will be totally effective in this regard because of various factors. In particular, a substantial portion of purchase, redemption and exchange orders are received through omnibus accounts. Omnibus accounts, in which shares are held in the name of an intermediary on behalf of multiple beneficial owners, are a common form of holding shares among financial intermediaries and retirement plans. The Fund typically is not able to identify trading by a particular beneficial owner through an omnibus account, which may make it difficult or impossible to determine if a particular account is engaged in market timing. Consequently, there is the risk that the Fund may not be able to identify, deter or curtail market timing that occurs in the Fund, which ma y result in certain shareholders being able to market time the Fund while the shareholders in the Fund bear the burden of such activities.

Certain financial intermediaries, including certain retirement plan service providers whose clients include, among others, various retirement plans sponsored by Bank of America and its affiliates for the benefit of its employees (the "Bank of America retirement plan service providers"), have different policies regarding monitoring and restricting market timing in the underlying beneficial owner accounts that they maintain through an omnibus account that may be more or less restrictive than the Fund practices discussed above. In particular, the Bank of America retirement plan service providers permit the reinstatement of future purchase orders for shares of the Fund following various suspension periods. If an intermediary does not enforce the Fund's policy, the intermediary must provide either data transparency to Columbia Management or Columbia Management must determine that the intermediary's policy taken in its entirety provid es protections to Fund shareholders that are generally commensurate with the Fund's policy.

The Fund seeks to act in a manner that it believes is consistent with the best interests of Fund shareholders in making any judgments regarding market timing. Neither the Fund nor its agents shall be held liable for any loss resulting from rejected purchase orders or exchanges.

FINANCIAL INTERMEDIARY PAYMENTS

The Fund's distributor, investment adviser or their affiliates may make payments, from their own resources, to certain financial intermediaries, including other Bank of America affiliates, for marketing support services. For purposes of this section the term "financial intermediary" includes any broker, dealer, bank, bank trust department, registered investment adviser, financial planner, retirement plan or other third-party administrator and any other institution having a selling, services or any similar agreement with the Fund's distributor, investment adviser or one of their affiliates. These payments are generally based upon one or more of the following factors: average net assets of the mutual funds distributed by the Fund's distributor attributable to that financial intermediary, gross sales of the mutual funds distributed by the Fund's distributor attributable to that financial intermediary, reimbursement of ticket charge s (fees that a financial intermediary firm charges its representatives for effecting transactions in fund shares) or a negotiated lump sum payment.

While the financial arrangements may vary for each financial intermediary, the support payments to any one financial intermediary are generally expected to be between 0.05% and 0.45% on an annual basis for payments

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based on average net assets of the Fund attributable to the financial intermediary, and between 0.10% and 0.25% on an annual basis for firms receiving a payment based on gross sales of the Fund attributable to the financial intermediary. The Fund's distributor, investment adviser or their affiliates may make payments in materially larger amounts or on a basis materially different from those described above when dealing with other affiliates of Bank of America. Such increased payments to the other Bank of America affiliate may enable the other Bank of America affiliate to offset credits that it may provide to its customers in order to avoid having such customers pay fees to multiple Bank of America entities in connection with the customer's investment in the Fund.

Payments also may be made to certain financial intermediaries, including other Bank of America affiliates, that provide investor services to retirement plans and other investment programs to compensate financial intermediaries for services they provide to such programs, including, but not limited to, sub-accounting, sub-transfer agency, similar shareholder or participant recordkeeping, shareholder or participant reporting, or shareholder or participant transaction processing. These payments for investor servicing support vary by financial intermediary but generally are not expected, with certain limited exceptions, to exceed 0.45% of the total Fund assets for Class Z shares in the program on an annual basis.

The Trust's Board of Trustees has authorized the Fund to pay to any intermediary up to 0.05% of the average aggregate value of Fund shares in the intermediary's program on an annual basis for providing investor services. Charges of an intermediary in excess of that paid by the Fund will be borne by the Fund's distributor or its affiliates.

The Fund's distributor, investment adviser or their affiliates may make other payments or allow promotional incentives to financial intermediaries to the extent permitted by the rules of the Securities and Exchange Commission, the National Association of Securities Dealers and by other applicable laws and regulations.

Amounts paid by the Fund's distributor, investment adviser or their affiliates are paid out of the distributor's, investment adviser's or their affiliates' own resources and do not increase the amount paid by you or the Fund. You can find further details about the payments made by the Fund's distributor, investment adviser or their affiliates and the services provided by financial intermediaries as well as a list of the financial intermediaries to which the Fund's distributor, investment adviser or their affiliates have agreed to make marketing support payments in the Fund's SAI, which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611. Your financial intermediary may charge you fees or commissions in addition to those disclosed in this prospectus. You can ask y our financial intermediary for information about any payments it receives from the Fund's distributor, investment adviser and their affiliates and any services your financial intermediary provides, as well as fees and/or commissions it charges. In addition, depending on the financial arrangement in place at any particular time, a financial intermediary and its financial consultants also may have a financial incentive for recommending a particular fund or share class over others. You should consult with your financial adviser and review carefully any disclosure by the financial intermediary as to compensation received by your financial adviser.

OTHER INFORMATION ABOUT YOUR ACCOUNT

How the Fund's Share Price is Determined The Fund's Class Z share price is based on its net asset value. The net asset value is determined at the close of regular trading on the NYSE, usually 4:00 p.m. Eastern time, on each business day that the NYSE is open for trading (typically Monday through Friday). Net asset value is not determined on days on which the NYSE is closed for trading.

When you request a transaction, it will be processed at the net asset value per share next determined after your request is received in "good form" by the distributor. In most cases, in order to receive that day's price, the Fund must receive your order before that day's transactions are processed. If you request a transaction through your

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financial advisor, your financial advisor must receive your order by the close of trading on the NYSE to receive that day's price.

The Fund determines its net asset value for its Class Z shares by dividing total net assets attributable to Class Z shares by the number of outstanding Class Z shares. In determining the net asset value, the Fund must determine the value of each security in its portfolio at the close of each trading day. Securities for which market quotations are available are valued each day at the current market value. However, where market quotations are unavailable, or when the adviser believes that subsequent events have made them unreliable, the Fund may use other data to determine the fair value of the securities.

The Fund has retained an independent statistical fair value pricing service to assist in the fair valuation process for securities principally traded in a foreign market in order to adjust for possible changes in value that may occur between the close of the foreign exchange and the time at which Fund shares are priced. The use of an independent fair value pricing service is intended to and may decrease the opportunities for time zone arbitrage transactions. There can be no assurance that the use of an independent fair value pricing service will successfully decrease arbitrage opportunities. If a security is valued at a "fair value," that value may be different from the last quoted market price for the security.

You can find the daily prices of some share classes for the Fund in most major daily newspapers under the heading of "Columbia." You can find daily prices for all share classes by visiting www.columbiafunds.com.

Share Certificates Share certificates are not available for Class Z shares.

Dividends, Distributions, and Taxes The Fund has the potential to make the following distributions:

Types of Distributions

Dividends	Represents interest and dividends earned from securities held by the Fund, net of expenses incurred by the Fund.
Capital gains	Represents net long-term capital gains on sales of securities held for more than one year and net short-term capital gains, which are gains on sales of securities held for a one-year period or less.

Distribution Options The Fund distributes any dividends in June and December and any capital gains (including short term capital gains) at least annually. You can choose one of the options listed in the table below for these distributions when you open your account. To change your distribution option call 1-800-345-6611.

If you do not indicate on your application or at the time your account is established your preference for handling distributions, the Fund will automatically reinvest all distributions in additional shares of the Fund.

UNDERSTANDING FUND DISTRIBUTIONS

The Fund may earn income from the securities it holds. The Fund also may realize capital gains or losses on sales of its securities. The Fund intends to distribute substantially all of its net investment income and capital gains to shareholders each year. As a shareholder, you are entitled to a portion of the Fund's income and capital gains based on the number of shares you own at the time these distributions are declared.

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Distribution Options

Reinvest all distributions in additional shares of the Fund

Reinvest all distributions in shares of another fund

Receive dividends in cash (see options below) and reinvest capital gains

Receive all distributions in cash (with one of the following options):

•  send the check to your address of record

•  send the check to a third-party address

•  transfer the money to your bank via electronic funds transfer

Distributions of $10 or less will automatically be reinvested in additional Fund shares. If you elect to receive distributions by check and the check is returned as undeliverable, all subsequent distributions will be reinvested in additional shares of the Fund.

Taxes Unless you are an entity exempt from income taxes or invest under a retirement account, regardless of whether you receive your distributions in cash or reinvest them in additional Fund shares, all Fund distributions are subject to federal income tax. Depending on where you live, distributions also may be subject to state and local income taxes.

The Fund intends to elect to be treated and to qualify each year as a regulated investment company. A regulated investment company is not subject to tax at the corporate level on income and gains from investments that are distributed to shareholders in accordance with applicable law. However, the Fund's failure to qualify as a regulated investment company could result in corporate level taxation, and consequently, a reduction in income available for distribution to shareholders.

In general, any distributions of dividends, interest and short-term capital gains (determined by how long the Fund held the investments that generated them) are taxable as ordinary income, unless such dividends are "qualified dividend income" (as defined in the Internal Revenue Code) eligible for a reduced rate of tax. Properly designated distributions of long-term capital gains (determined by how long the Fund held the investments that generated them) are generally taxable as such, regardless of how long you have held your Fund shares. You will be provided with information each year regarding the amount of ordinary income and capital gains distributed to you for the previous year and any portion of your distribution which is exempt from state and local taxes. Long-term capital gain rates have been reduced — in general, to 15% with lower rates applying to taxpayers in the 10% and 15% rate brackets — for taxable years b eginning before January 1, 2011. Distributions are taxable to you even if they are paid from income or gains earned by the Fund before you made your investment (and thus were included in the price you paid). Your investment in the Fund may have additional personal tax implications. Please consult your tax advisor about foreign, federal, state, local or other applicable tax laws.

In addition to the dividends and capital gains distributions made by the Fund, you may realize a capital gain or loss when selling or exchanging shares of the Fund. Such transactions also may be subject to federal, state and local income tax.

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Board of Trustees

The Fund is governed by its Board of Trustees. More than 75% of the Fund's Trustees are independent, meaning that they have no affiliation with the adviser or the Funds, apart from their positions as Trustees and the personal investments they may have made as private individuals.

The independent Trustees bring backgrounds in business and the professions and academia to their task of working with the Funds' officers to establish the policies and oversee the activities of the Funds. Among the Trustees' responsibilities are selecting the investment adviser for the Funds; negotiating the advisory agreements; reviewing other contracts; approving investment policies; monitoring Fund operations, performance, and costs; and nominating or selecting new Trustees.

Each Trustee serves until his or her retirement, resignation, death or removal; or otherwise as specified in the Trust's organizational documents. It is expected that every five years the Trustees will call a meeting of shareholders to elect Trustees. A Trustee must retire at the end of the year in which he or she attains the age of 75. Any Trustee may be removed at a shareholders' meeting by a vote representing two-thirds of the net asset value of all shares of the Funds of the Trust. The mailing address for the Trustees and officers is 227W.Monroe, Suite 3000, Chicago, Illinois 60606.

For more detailed information on the Board of Trustees, please refer to the SAI.

Managing the Fund

INVESTMENT ADVISER

Columbia Wanger Asset Management, L.P. (CWAM), located at 227 West Monroe Street, Suite 3000, Chicago, Illinois 60606, is the Fund's investment adviser and is responsible for the Fund's management, subject to the oversight of the Fund's Board of Trustees. CWAM and its predecessor have managed mutual funds, including the Fund, since 1992. In its duties as investment adviser, CWAM runs the Fund's day-to-day business, including making investment decisions and placing all orders for the purchase and sale of the Fund's portfolio securities.

CWAM was previously named Liberty Wanger Asset Management, L.P. and its predecessor was named Wanger Asset Management, L.P. (WAM). CWAM is a wholly owned subsidiary of Columbia Management Group, LLC, which is an indirect wholly owned subsidiary of Bank of America Corporation. As of December 31, 2006, CWAM managed more than $32.9 billion in assets.

CWAM's advisory fee for managing the Fund in 2006 was 0.82% of the Fund's average daily net assets. CWAM also received an administrative fee from the Fund in 2006 of 0.04% of the Fund's average daily net assets. A discussion of the factors considered by the Fund's Board of Trustees in approving the Fund's investment advisory contract is included in the Fund's annual report to shareholders for the period ended December 31, 2006.

PORTFOLIO MANAGER

CWAM uses a team to assist the lead portfolio manager in managing the Fund. Team members share responsibility for providing ideas, information and knowledge in managing the Fund, and each team member has

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Managing the Fund

one or more particular areas of expertise. The portfolio manager is responsible for making daily investment decisions and utilizing the management team's input and advice when making buy and sell determinations.

Ben Andrews
Lead portfolio manager
Ben Andrews has managed Columbia Acorn Select since March 2004. He is a vice president of the Trust and has been part of the CWAM investment team since 1998, most recently as a senior technology analyst. His analytical experience includes covering a broad range of industries and special situations. Mr. Andrews also is a vice president of Wanger Advisors Trust and the lead portfolio manager of Wanger Select, a mutual fund underlying variable insurance products.

The SAI provides additional information about the portfolio manager's compensation, other accounts managed and ownership of securities in the Fund.

LEGAL PROCEEDINGS

The Trust, CWAM and the trustees of the Trust (collectively the "Columbia defendants") are named as defendants in class and derivative complaints, which were consolidated in a Multi-District Action in the federal district court for the District of Maryland on February 20, 2004 (the "MDL Action"). These lawsuits contend that defendants permitted certain investors to market time their trades in certain Columbia Acorn Funds. The MDL Action is ongoing. All claims against the Trust and its independent trustees have been dismissed; however, the interested trustees of the Trust are still parties to the MDL Action.

On March 21, 2005, a class action complaint was filed against the Trust in the Superior Court of the Commonwealth of Massachusetts seeking to rescind the contingent deferred sales charges assessed upon redemption of Class B shares of Columbia Acorn Funds due to the alleged market timing of the Columbia Acorn Funds. In addition to the rescission of sales charges, plaintiffs seek recovery of actual damages, attorneys' fees and costs. The case has been transferred to the MDL Action in the federal district court of Maryland.

The Trust and CWAM are also defendants in a class action lawsuit, filed on November 13, 2003 in the Circuit Court of the Third Judicial Circuit, Madison County, Illinois, that alleges, in summary, that the Trust and CWAM exposed shareholders of Columbia Acorn International to trading by market timers by allegedly (a) failing to properly evaluate daily whether a significant event affecting the value of that fund's securities had occurred after foreign markets had closed but before the calculation of the Fund's net asset value; (b) failing to implement the fund's portfolio valuation and share pricing policies and procedures; and (c) failing to know and implement applicable rules and regulations concerning the calculation of net asset value ("Fair Valuation Lawsuit"). On April 5, 2005, the United States Court of Appeals for the Seventh Circuit ruled that the plaintiffs' state law claims were preempted under federal law resulting in the dismissal of plaintiffs' complaint. Plaintiffs appealed the Seventh Circuit's ruling to the United States Supreme Court. On June 15, 2006, the Supreme Court reversed the Seventh Circuit's ruling on jurisdictional grounds, and the case ultimately was remanded to the state court.

On April 4, 2006, the plaintiffs and the Columbia defendants named in the MDL Action executed an agreement in principle intended to fully resolve all of the lawsuits consolidated in the MDL Action as well as the Fair Valuation Lawsuit. The court entered a stay after the parties executed the agreement in principle. The settlement is subject to court approval.

18

Managing the Fund

In 2004, CWAM and the trustees of the Columbia Acorn Trust were named as defendants in certain purported shareholder class and derivative actions making claims, including claims under the Investment Company and the Investment Advisers Acts of 1940 and state law. Certain Columbia Acorn Funds were named as nominal defendants. The suits allege, inter alia, that the fees and expenses paid by the funds are excessive and that the funds' advisers and their affiliates inappropriately used fund assets to distribute the funds and for other improper purposes. On March 2, 2005, the actions were consolidated in the Massachusetts federal court as In re Columbia Entities Litigation. The plaintiffs filed a consolidated amended complaint on June 9, 2005. On November 30, 2005, the judge dismissed all claims by plaintiffs and entered final judgment in favor of the defendants. The plaintiffs appealed to the United States Court of Appeals for the First Circuit on December 30, 2005. A stipulation and settlement agreement dated January 19, 2007 was filed in the First Circuit on February 14, 2007, with a joint stipulation of dismissal and motion for remand to obtain district court approval of the settlement. The joint motion was granted and the appeal was dismissed. On March 6, 2007, the case was remanded to the District Court, where the parties will seek court approval of the settlement. The terms of the proposed settlement, if approved, will require payments by the funds' adviser and/or its affiliates, including payment of plaintiffs' attorneys' fees and notice to class members. In the event that the settlement is not approved, the plaintiffs may elect to g o forward with their appeal and no opinion is expressed regarding the likely outcome or financial impact of such an appeal on any fund.

On or about January 11, 2005, a putative class action lawsuit was filed in federal district court in Massachusetts against the Trust and its trustees, along with Columbia Management Advisors, LLC, the sub-administrator of the Wanger Advisors Funds and the Columbia Acorn Funds. The plaintiffs allege that the defendants failed to submit Proof of Claims in connection with settlements of securities class action lawsuits filed against companies in which the Columbia Acorn Funds held positions. The complaint seeks compensatory and punitive damages, and the disgorgement of all fees paid to Columbia Management Advisors, LLC. Plaintiffs have voluntarily dismissed the Trust and its independent trustees.

The Trust and CWAM intend to defend these suits vigorously.

As a result of these matters or any adverse publicity or other developments resulting from them, there may be increased redemptions or reduced sales of Fund shares, which could increase transaction costs or operating expenses, or have other adverse consequences for the Fund.

However, based on currently available information, the Trust believes that the likelihood that these lawsuits will have a material adverse impact on any fund is remote, and CWAM believes that the lawsuits are not likely to materially affect its ability to provide investment management services to the Fund.

Other Investment Strategies and Risks

The Fund's principal investment strategies and associated risks are described under "The Fund — Principal Investment Strategies" and "The Fund — Principal Investment Risks." This section describes other investments the Fund may make and the risks associated with them. In seeking to achieve its investment goal, the Fund may

19

Other Investment Strategies and Risks

invest in various types of securities and engage in various investment techniques which are not the principal focus of the Fund and therefore are not described in this prospectus. The Fund may not always achieve its investment goal. These types of securities and investment practices and their associated risks are identified and discussed in the Fund's SAI, which you may obtain free of charge (see back cover). The adviser may elect not to buy any of these securities or use any of these techniques. The Fund may not always achieve its investment goal. Except as otherwise noted, approval by the Fund's shareholders is not required to modify or change the Fund's investment strategies.

THE INFORMATION EDGE

The Fund generally invests in entrepreneurially managed smaller- and mid-sized companies that it believes are not as well known by financial analysts as the largest companies and whose position in a niche creates the opportunity for superior earnings-growth potential. CWAM may identify what it believes are important economic, social or technological trends (for example, the growth of outsourcing as a business strategy, or the productivity gains from the increasing use of technology) and try to identify companies it thinks will benefit from those trends.

In making investments for the Fund, CWAM relies primarily on independent, internally generated research to uncover companies that may be less well known than the more popular names. To find these companies, CWAM compares growth potential, financial strength and fundamental value among companies.

Growth Potential	Financial Strength	Fundamental Value
• superior technology • innovative marketing • managerial skill • market niche • good earnings prospects • strong demand for product	• low debt • adequate working capital • conservative accounting practices • adequate profit margin	• reasonable stock price relative to growth potential and financial strength • valuable assets
The realization of this growth potential would likely produce superior performance that is sustainable over time.	A strong balance sheet gives management greater flexibility to pursue strategic objectives and is important to maintaining a competitive advantage.	Once CWAM uncovers an attractive company, it identifies a price that it believes would also make the stock a good value.

LONG-TERM INVESTING

CWAM's analysts continually screen companies and make contact with more than 1,000 companies around the globe each year. To accomplish this, CWAM analysts often talk directly to top management, vendors, suppliers and competitors.

In managing the Fund, CWAM tries to maintain lower taxes and transaction costs by investing with a long-term time horizon (at least two to five years). However, securities purchased on a long-term basis may be sold within 12 months after purchase due to changes in the circumstances of a particular company or industry, or changes in general market or economic conditions.

20

Other Investment Strategies and Risks

DERIVATIVE STRATEGIES

The Fund may enter into a number of derivative strategies, including those that employ futures, options, straddles or similar transactions, to gain or reduce exposure to particular securities or markets. These strategies, commonly referred to as derivatives, involve the use of financial instruments whose values depend on, or are derived from, the value of an underlying security, index or currency. The Fund may use these strategies to adjust the Fund's sensitivity to changes in interest rates, or for other hedging purposes (i.e., attempting to offset a potential loss in one position by establishing an interest in an opposite position). Derivative strategies involve the risk that they may exaggerate a loss, potentially losing more money than the actual cost of the underlying security, or limit a potential gain. Also, with some derivative strategies there is a risk that the other party to the transaction may fail to honor its contr act terms, causing a loss to the Fund or that the Fund may not be able to find a suitable derivative transaction counterparty, and thus may be unable to invest in derivatives altogether.

TEMPORARY DEFENSIVE STRATEGIES

At times, CWAM may determine that adverse market conditions make it desirable to temporarily suspend the Fund's normal investment activities. During such times, the Fund may, but is not required to, invest in cash or high-quality, short-term debt securities, without limit. Taking a temporary defensive position may prevent the Fund from achieving its investment goal.

21

Financial Highlights

The financial highlights table is intended to help you understand the Fund's Class Z financial performance. Information is shown for the Fund's last five fiscal years, which run from January 1 to December 31. Certain information in the table reflects the financial results for a single Class Z share. The total returns in the table represent the return that you would have earned (or lost) on an investment in the Fund (assuming reinvestment of all dividends and distributions). This information has been derived from the Fund's financial statements, which have been audited for the years ended December 31, 2004, 2005 and 2006 by PricewaterhouseCoopers LLP, an independent registered public accounting firm, whose report, along with the Fund's financial statements, is included in the Fund's annual report. The information for the years ended December 31, 2002 and 2003 is included in the Fund's financial statements that have been audited b y another independent registered public accounting firm, whose report expressed an unqualified opinion on those financial statements and highlights. You can request a free annual report containing those financial statements by calling 1-800-345-6611.

Columbia Acorn Select

	Year Ended December 31,
	2006			2005			2004			2003			2002
	Class Z			Class Z			Class Z			Class Z			Class Z
Net asset value — Beginning of period ($)		22.77			21.13			18.20			14.04			15.23
Income from Investment Operations ($)
Net investment loss(a)		(0.06	)		(0.03	)		(0.10	)		(0.10	)		(0.10	)
Net realized and unrealized gain (loss)		4.51			2.35			3.47			4.39			(1.09	)
Total from Investment Operations		4.45			2.32			3.37			4.29			(1.19	)
Less Distributions Declared to Shareholders ($):
From net investment income		(0.04	)		—			—			—			—
From net realized gains		(0.59	)		(0.68	)		(0.44	)		(0.13	)		—
Total Distributions Declared to Shareholders		(0.63	)		(0.68	)		(0.44	)		(0.13	)		—
Net asset value — End of period ($)		26.59			22.77			21.13			18.20			14.04
Total return (%)(b)		19.68	(c)		11.08	(c)		18.58	(c)		30.61			(7.81	)(c)
Ratios to Average Net Assets/Supplemental Data (%):
Expenses(d)		0.96			0.99			1.13			1.12			1.26
Net investment loss		(0.26	)		(0.16	)(d)		(0.52	)(d)		(0.63	)(d)		(0.67	)(d)
Waiver/reimbursement		0.02			0.03			0.02			—			0.01
Portfolio turnover rate (%)		21			19			34			16			40
Net assets at end of period (in millions) ($)		909			688			445			294			93

(a)  Per share data was calculated using average shares outstanding during the period.

(b)  Total return at net asset value assuming all distributions reinvested.

(c)  Had the investment adviser and/or transfer agent not waived and/or reimbursed a portion of expenses, total return would have been reduced.

(d)  The benefits derived from custody fees paid indirectly had no impact.

22

Appendix

Hypothetical Investment and Expense Information

The Fund is required to disclose the following supplemental hypothetical investment information, which provides additional information about the effect of the expenses paid by the Fund, including investment advisory fees and other Fund costs, on the Fund's returns over a 10-year period. The table shows the estimated expenses that would be charged on a hypothetical investment of $10,000 in Class Z shares of the Fund assuming a 5% return each year, the cumulative return after fees and expenses, and the hypothetical year-end balance after fees and expenses. The table also assumes that all dividends and distributions are reinvested. The annual expense ratio used for the Fund, which is the same as that stated in the Annual Fund Operating Expenses table, is presented in the table, and is net of any contractual fee waivers or expense reimbursements for the period of the contractual commitment. Your actual costs may be higher or lower. As noted previously, the Fund's minimum investment for initial purchases or exchanges is $50,000.

Columbia Acorn Select — Class Z Shares

Maximum Sales Charge 0.00%					Initial Hypothetical Investment Amount $10,000.00						Assumed Rate of Return 5%
Year		Cumulative Return Before Fees & Expenses			Annual Expense Ratio			Cumulative Return After Fees & Expenses			Hypothetical Year-End Balance After Fees & Expenses		Annual Fees & Expenses(1)
	1		5.00	%		0.98	%		4.02	%	$	10,402.00	$	99.97
	2		10.25	%		0.98	%		8.20	%	$	10,820.16	$	103.99
	3		15.76	%		0.98	%		12.55	%	$	11,255.13	$	108.17
	4		21.55	%		0.98	%		17.08	%	$	11,707.59	$	112.52
	5		27.63	%		0.98	%		21.78	%	$	12,178.23	$	117.04
	6		34.01	%		0.98	%		26.68	%	$	12,667.80	$	121.75
	7		40.71	%		0.98	%		31.77	%	$	13,177.04	$	126.64
	8		47.75	%		0.98	%		37.07	%	$	13,706.76	$	131.73
	9		55.13	%		0.98	%		42.58	%	$	14,257.77	$	137.03
	10		62.89	%		0.98	%		48.31	%	$	14,830.93	$	142.53
Total Gain After Fees and Expenses											$	4,830.93
Total Annual Fees and Expenses													$	1,201.37

(1)  Annual Fees and Expenses are calculated based on the average between the beginning and ending balance for each year. All information is calculated on an annual compounding basis.

23

Notes

24

Notes

25

Notes

26

FOR MORE INFORMATION

Additional information about the Fund's investments is available in the Fund's semiannual and annual reports to shareholders. The annual report contains a discussion of the market conditions and investment strategies that significantly affected the Fund's performance during its last fiscal year.

You may wish to read the SAI for more information on the Fund and the securities in which it invests. The SAI is incorporated into this prospectus by reference, which means that it is considered to be part of this prospectus.

You can get free copies of annual and semiannual reports and the SAI, request other information and discuss your questions about the Fund by visiting www.columbiafunds.com or by writing or calling the Fund's transfer agent at:

Columbia Management Services, Inc.
P.O. Box 8081
Boston, MA 02266-8081
1-800-345-6611

Text-only versions of all Fund documents can be viewed online or downloaded from the EDGAR database on the Securities and Exchange Commission internet site at www.sec.gov.

You can review and copy information about the Fund, including the SAI, by visiting the following location, and you can obtain copies upon payment of a duplicating fee, by electronic request at the e-mail address publicinfo@sec.gov or by writing the:

Public Reference Room
Securities and Exchange Commission
Washington, DC 20549-0102

Information on the operation of the Public Reference Room may be obtained by calling 1-202-942-8090.

Investment Company Act file number:
Columbia Acorn Trust: 811-01829
•  Columbia Acorn Select

©2007 Columbia Management Distributors, Inc.
One Financial Center, Boston, MA 02111-2621
800.426.3750 www.columbiafunds.com

INT-36/130311-0507

Columbia^SM

Thermostat Fund^SM  Prospectus, May 1, 2007

Class A, B and C Shares

Advised by Columbia Wanger Asset Management, L.P.

TABLE OF CONTENTS

THE FUND	2
Investment Goal	2
Principal Investment Strategies	2
Principal Investment Risks	10
Portfolio Holdings Disclosure	14
Performance History	14
Commissions and Other Expenses	16
YOUR ACCOUNT	19
Choosing a Share Class	19
How to Buy Shares	20
Investment Minimums	20
Sales Charges (Commissions)	21
How to Exchange Shares	26
How to Sell Shares	27
Fund Policy on Trading of Fund Shares	28
Other Information About Your Account	30
BOARD OF TRUSTEES	33
MANAGING THE FUND	33
Investment Adviser	33
Portfolio Manager	34
Legal Proceedings	34
OTHER INVESTMENT STRATEGIES AND RISKS	36
Derivative Strategies	36
When-Issued Securities and Forward Commitments	37
Short Sales	37
Asset-Backed Securities	37
Mortgage-Backed Securities	37
Zero Coupon Bonds	38
Illiquid Investments	38
Temporary Defensive Strategies	38
FINANCIAL HIGHLIGHTS	39
APPENDIX A	42
APPENDIX B	45

Although these securities have been registered with the Securities and Exchange Commission, the Commission has not approved or disapproved any shares offered in this prospectus or determined whether this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Acorn Thermostat is a trademark owned and registered by Columbia Acorn Trust, Columbia, Columbia Management^® and Columbia Management Services, Inc. are service marks owned and/or registered by Bank of America

The Fund

INVESTMENT GOAL

Columbia Thermostat Fund (Thermostat Fund^SM or Thermostat) seeks to provide long-term total return.

PRINCIPAL INVESTMENT STRATEGIES

Thermostat Fund pursues its investment goal by investing in other mutual funds. As a "fund of funds," under normal circumstances, Thermostat allocates at least 95% of its net assets (stock/bond assets) among a selected group of stock and bond mutual funds (Portfolio Funds) according to the current level of the Standard & Poor's 500 Stock Index (S&P 500) in relation to predetermined ranges set by the Fund's investment adviser. When the S&P 500 goes up, the Fund sells a portion of its stock funds and invests more in the bond funds; and when the S&P 500 goes down, the Fund increases its investment in the stock funds. Under normal circumstances, Thermostat may invest up to 5% of its net assets plus any cash received that day in cash, high quality short-term paper and government securities.

Asset allocation funds generally move assets from stocks to bonds when the market goes up, and from bonds to stocks when the market goes down. Most asset allocation funds are run by sophisticated investment professionals, who make subjective decisions based on economic and financial data and complex graphs of market behavior. By contrast, the day-to-day investment decisions for Thermostat are made according to a single predetermined rule. The temperature in your house is run by a single rule; your thermostat turns on the furnace if your house is too cold or turns on the air conditioner if your house is too warm. This Fund works the same way, so it is named Thermostat Fund.

Because Thermostat invests according to a pre-set program, there is no need for subjective day-to-day management. Although another successful asset allocation strategy might do better than Thermostat, Thermostat is designed for those who doubt the wisdom of trying to "time" the market and are unsure of the long-term trend of the stock market. Thermostat takes psychology out of investing; it avoids the temptation to buy more stocks because the stock market is currently going up or to sell stocks because the market is declining. Thermostat operates continuously and substantially automatically, subject to periodic review of the pre-set program by Thermostat Fund's adviser and its Board of Trustees. As described on page 3, the portfolio manager has Thermostat's adviser will have authority to review the structure and allocation ranges of the stock-bond allocation table and to make any changes considered appropriate.

The Portfolio Funds are chosen by Thermostat's adviser to provide participation in the major sectors of the stock and bond markets. If you believe that the stock market will tend to go up most of the time, then you should probably own a fully-invested stock fund and use a buy-and-hold strategy. Buy-and-hold was an excellent strategy in the 1982-1999 bull market. However, there have been long periods in the past when buy-and-hold was not the best strategy, such as 1930-1954 and 1969-1981, when the market fluctuated but did notmake significant new highs. Thermostat may be a good investment choice for you if you believe that the market may fluctuate in a trading range for many years, a remarkable bull market ended early in 2000 and that the market may not reach significant new highs for many years.

2

The Fund

Thermostat invests the stock/bond assets among the Portfolio Funds according to an asset allocation table. The current allocation table is set forth below:

Stock/Bond Allocation Table

	How Thermostat will Invest the Stock/Bond Assets
Level of the S&P 500	Stock Percentage			Bond Percentage
over 1800		0	%		100	%
over 1750-1800		5			95
over 1700-1750		10			90
over 1650-1700		15			85
over 1600-1650		20			80
over 1550-1600		25			75
over 1500-1550		30			70
over 1450-1500		35			65
over 1400-1450		40			60
over 1350-1400		45			55
over 1300-1350		50			50
over 1250-1300		55			45
over 1200-1250		60			40
over 1150-1200		65			35
over 1100-1150		70			30
over 1050-1100		75			25
over 1000-1050		80			20
over 950-1000		85			15
over 900-950		90			10
over 850-900		95			5
850 and under		100			0

When the S&P 500 moves into a new band on the table, the Fund promptly will rebalance the stock-bond mix to reflect the new S&P price level by redeeming shares of some Portfolio Funds and purchasing shares of other Portfolio Funds. The only exception will be a "31-day Rule"; in order to reduce taxable events, after the Fund has increased its percentage allocation to either stock funds or bond funds, it will not decrease that allocation for at least 31 days. Following a change in the Fund's stock-bond mix, if the S&P 500 remains within the same band for a while, normal market fluctuations will change the values of the Fund's holdings of stock Portfolio Funds and bond Portfolio Funds. We will invest cash flows from sales (or redemptions) of Fund shares to bring the stock-bond mix back toward the allocation percentages for that S&P 500 band. For example, if the S&P 500 is in the 1000-1050 band, and the value of the holdings of the stock Portfolio Funds has dropped to 68% of the value of the holdings of all Portfolio Funds, new cash would be invested in the stock Portfolio Funds (or cash for redemptions would come from the bond Portfolio Funds). If the 31-day Rule is in effect, new cash flows will be invested at the stock-bond percentage allocation as of the latest rebalancing.

3

The Fund

As an illustrative example, suppose the following market events occurred:

Date	Level of the S&P 500	How Thermostat will invest the Stock/Bond Assets
Nov. 1	We begin when the market is 1340	50% stocks, 50% bonds
Dec. 1	The S&P 500 goes to 1351	rebalance 45% stocks, 55% bonds
Dec. 6	The S&P 500 drops back to 1345	no reversal for 31 days
Jan. 2	The S&P 500 is at 1342	rebalance 50% stocks, 50% bonds
Jan. 20	The S&P 500 drops to 1299	rebalance 55% stocks, 45% bonds
	The market has made a continuation move by going through a second action level, not a reversal move, so the 31-day Rule does not apply in this case.
Jan. 30	The S&P 500 goes up to 1305	no reversal for 31 days
Feb. 20	The S&P 500 is at 1310	rebalance 50% stocks, 50% bonds

The following table shows the six stock Portfolio Funds and three bond Portfolio Funds that Thermostat currently uses in its fund-of-funds structure and the current allocation percentage for each Portfolio Fund within the stock or bond category. The allocation percentage within each category is achieved by rebalancing the investments within the category whenever the S&P 500 moves into a new band on the allocation table, subject to the 31-day Rule described above. Thermostat does not liquidate its investment in one Portfolio Fund in order to invest in another Portfolio Fund except in connection with a rebalancing due to a move of the S&P 500 into a new band (or due to a change by the portfolio manager in the stock-bond allocation table in the Portfolio Funds or in the relative allocation among Portfolio Funds). Until a subsequent rebalancing, Thermostat's investments in, and redemptions from, the stock Portfolio Funds or the bond Portfolio Funds are allocated among such Portfolio Funds in a manner that will reduce any deviation of the relative values of Thermostat's holdings of such funds from the allocation percentages shown below.

Allocation of Stock/Bond Assets within Asset Classes

Stock Funds	Type of Fund	Allocation
Columbia Acorn Fund	Small-/Mid-cap growth		15	%
Columbia Acorn Select	Mid-cap growth		10	%
Columbia Marsico Growth Fund	Large-cap growth		15	%
Columbia Acorn International	Small/mid-cap international growth		15	%
Columbia Dividend Income Fund	Large-cap value		20	%
Columbia Large Cap Enhanced Core Fund(1)	Large-cap blend		25	%
Total			100	%
Bond Funds	Type of Fund	Allocation
Columbia Federal Securities Fund	U.S. government securities		30	%
Columbia Intermediate Bond Fund	Intermediate-term bonds		50	%
Columbia Conservative High Yield Fund	High-yield bonds		20	%
Total			100	%

(1)  Nations LargeCap Enhanced Core Fund changed its name on September 26, 2005 to Columbia Large Cap Enhanced Core Fund.

As described below, Thermostat's portfolio manager will have authority to review the Portfolio Funds and the relative allocation percentages among the stock funds and among the bond funds and to make any changes considered appropriate.

4

The Fund

Thermostat is advised by Columbia Wanger Asset Management, L.P. (CWAM or the adviser). Each of the Portfolio Funds is managed by CWAM or an affiliate of CWAM. The Fund will not pay any sales load on its purchases of shares of the Portfolio Funds.

On an annual basis, or on an "emergency" basis if necessary, the portfolio manager reviews the structure, allocation percentages and Portfolio Funds of Thermostat and makes any changes considered appropriate. The portfolio manager typically addresses the following questions:

Should the stock-bond allocation table be revised? (perhaps because the stock market has made a long-term move outside of the 750-1700 S&P 500 bands)

Should there be a change in the Portfolio Funds in which Thermostat invests, or should there be a change in the percentage allocations among the stock funds or the bond funds? (perhaps because of a change of portfolio managers, change of investment style or reorganization of a Portfolio Fund)

Any changes by the portfolio manager are expected to be infrequent.

The S&P 500 is a broad market-weighted average of 500 widely-held large capitalization U.S. stocks.

The investment objectives and strategies of the current Portfolio Funds are described below:

Additional strategies that are not principal investment strategies and the risks associated with them are described below under "Other Investment Strategies and Risks."

Columbia Acorn Fund, Class Z (Acorn^® Fund)

Acorn Fund seeks to provide long-term growth of capital.

Acorn Fund generally invests in the stocks of small- and medium-sized companies. The Fund generally invests in the stocks of companies with market capitalizations of less than $5 billion at the time of initial purchase. As long as a stock continues to meet the Fund's other investment criteria, the Fund may choose to hold the stock even if it grows beyond an arbitrary capitalization limit.

Acorn Fund believes that these smaller companies, which are not as well known by financial analysts, may offer higher return potential than the stocks of larger companies.

Acorn Fund typically looks for companies with:

•  A strong business franchise that offers growth potential.

•  Products and services that give a company a competitive advantage.

•  A stock price the Fund's adviser believes is reasonable relative to the assets and earning power of the company.

Acorn Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its assets in companies outside the United States in developed markets (for example, Japan, Canada and the United Kingdom) and emerging markets (for example, Mexico, Brazil and Korea).

Columbia Acorn Select, Class Z (Acorn Select^SM)

Acorn Select seeks long-term growth of capital.

Acorn Select generally invests in the stocks of U.S. companies. The Fund is a non-diversified fund that takes advantage of its adviser's research and stock-picking capabilities to invest in a limited number of companies

5

The Fund

(between 20-40) with market capitalizations under $20 billion at the time of initial purchase, offering the potential to provide above-average growth over time.

Acorn Select believes that companies within this capitalization range, which are not as well known by financial analysts as the largest companies, may offer higher return potential than the stocks of companies with capitalizations above $20 billion.

Acorn Select typically looks for companies with:

•  A strong business franchise that offers growth potential.

•  Products and services that give a company a competitive advantage.

•  A stock price the Fund's adviser believes is reasonable relative to the assets and earning power of the company.

Although Acorn Select does not buy securities with a short-term view, there is no restriction on the length of time the Fund must hold a security. To the extent the Fund buys and sells securities frequently, its transaction costs will be higher (which may adversely affect the Fund's performance) and it may realize additional capital gains.

The Fund invests the majority of its assets in U.S. companies, but also may invest up to 25% of its assets in companies outside the United States in developed markets (for example, Japan, Canada and the United Kingdom) and emerging markets (for example, Mexico, Brazil and Korea).

Columbia Marsico Growth Fund, Class Z (Marsico Growth Fund)

Marsico Growth Fund seeks long-term growth of capital.

Marsico Growth Funds invests all of its assets in Columbia Marsico Growth Master Portfolio (the Master Portfolio). The Master Portfolio has the same investment objective as Marsico Growth Fund.

The Master Portfolio invests primarily in equity securities of large-capitalization companies with a market capitalization of $4 billion or more that are selected for their growth potential. It generally holds a core position of between 35 and 50 common stocks. It may hold up to 25% of its assets in foreign securities.

The Master Portfolio may also invest in securities that aren't part of its principal investment strategies, but it won't hold more than 10% of its assets in any one type of these securities.

In selecting investments for the Master Portfolio, the investment adviser uses an approach that combines "top-down" macroeconomic analysis with "bottom-up" stock selection.

The "top-down" approach may take into consideration macroeconomic factors such as, without limitation, interest rates, inflation, demographics, the regulatory environment and the global competitive landscape. In addition, the investment adviser may also examine other factors that may include, without limitation, the most attractive global investment opportunities, industry consolidation, and the sustainability of financial trends observed. As a result of the "top-down" analysis, the investment adviser seeks to identify sectors, industries and companies that may benefit from the overall trends the investment adviser has observed.

The investment adviser then looks for individual companies or securities with earnings growth potential that may not be recognized by the market at large. In determining whether a particular company or security may be a suitable investment, the investment adviser may focus on any of a number of different attributes that may include, without limitation, the company's specific market expertise or dominance; its franchise durability and pricing

6

The Fund

power; solid fundamentals (e.g., a strong balance sheet, improving returns on equity, the ability to generate free cash flow, apparent use of conservative accounting standards and transparent financial disclosure); strong and ethical management; commitment to shareholder interests; reasonable valuations in the context of projected growth rates; and other indications that a company or security may be an attractive investment prospect.

This process is called "bottom-up" stock selection.

As part of this fundamental, "bottom-up" research, the investment adviser may visit with various levels of a company's management, as well as with its customers and (as relevant) suppliers, distributors and competitors. The investment adviser also may prepare detailed earnings and cash flow models of companies. These models may assist the investment adviser in projecting potential earnings growth and other important company financial characteristics under different scenarios. Each model is typically customized to follow a particular company and is generally intended to replicate and describe a company's past, present and potential future performance. The models may include quantitative information and detailed narratives that reflect updated interpretations of corporate data and company and industry developments.

The investment adviser may reduce or sell investments in portfolio companies if, in the opinion of the investment adviser, a company's fundamentals change substantially, its stock price appreciates excessively in relation to fundamental earnings growth prospects, the company appears not to realize its growth potential, or there are more attractive investment opportunities elsewhere. The Master Portfolio's core investments generally are comprised of established companies and securities that exhibit growth characteristics. However, the Master Portfolio also may typically include companies with more aggressive growth characteristics and companies undergoing significant changes: e.g., the introduction of a new product line, the appointment of a new management team, or an acquisition.

Marsico Growth Fund could withdraw its entire investment from the Master Portfolio if it believes it's in the best interests of the Fund to do so (for example, if the Master Portfolio changed its investment objective). It is unlikely that this would happen, but if it did, Marsico Growth Fund's portfolio could be less diversified and therefore less liquid, and expenses could increase. Marsico Growth Fund might also have to pay brokerage, tax or other charges.

Columbia Acorn International, Class Z (Acorn International^®)

Acorn International seeks to provide long-term growth of capital.

Acorn International generally invests in stocks of non-U.S. small- and medium-sized companies. The Fund generally invests in the stocks of companies based outside the United States with market capitalizations of less than $5 billion at the time of initial purchase. As long as a stock continues to meet the Fund's other investment criteria, the Fund may choose to hold the stock even if it grows beyond an arbitrary capitalization limit.

Acorn International believes that smaller companies, predominantly outside the United States, that are not as well known by financial analysts, may offer higher return potential than the stocks of larger companies.

Acorn International typically looks for companies with:

•  A strong business franchise that offers growth potential.

•  Products and services that give the company a competitive advantage.

•  A stock price the Fund's investment adviser believes is reasonable relative to the assets and earning power of the company.

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The Fund

Acorn International is an international fund and invests the majority (under normal market conditions, at least 75%) of its total assets in the stocks of foreign companies based in developed markets (for example, Japan, Canada and the United Kingdom) and emerging markets (for example, Mexico, Brazil and Korea).

Columbia Dividend Income Fund, Class Z (Dividend Income Fund)

Dividend Income Fund seeks current income and capital appreciation.

Under normal market conditions, Dividend Income Fund invests at least 80% of its net assets (plus any borrowings for investment purposes) in a diversified portfolio of income-producing (dividend-paying) equity securities, which will consist primarily of common stocks but may also include preferred stocks and convertible securities. The Fund's investment adviser looks for investments that it believes offer prospects for dividend growth and capital appreciation.

The Fund generally will emphasize value stocks, but may purchase growth securities when such securities pay dividends or the adviser believes such securities have particularly good prospects for capital appreciation. In addition to equity securities, the Fund may also invest up to 20% of its net assets in debt securities, including lower-quality debt securities. The Fund may invest up to 20% of its net assets in securities of foreign issuers.

At times, the investment adviser may determine that adverse market conditions make it desirable to suspend temporarily the Fund's normal investment activities. During such times, the Fund may, but is not required to, invest in cash or high-quality, short-term debt securities, without limit. Taking a temporary defensive position may prevent the Fund from achieving its investment goal.

Columbia Large Cap Enhanced Core Fund, Class Z (Core Fund)

Core Fund seeks, over the long term, to provide a total return that (before fees and expenses) exceeds the total return of the S&P 500 Index.

Under normal circumstances, Core Fund will invest at least 80% of its assets in a portfolio consisting of common stocks that are included in the S&P 500 Index, convertible securities that are convertible into stocks included in that index, and other derivatives whose economic returns are, by design, closely equivalent to the returns of the S&P 500 Index or its components. The S&P 500 Index is an unmanaged index of 500 widely held common stocks, and is not available for investment.

The portfolio manager tries to maintain a portfolio that matches the risk characteristics of the S&P 500 Index. The portfolio manager will, from time to time, vary the number and percentages of the Fund's holdings to try to provide higher returns than the S&P 500 Index and to reduce the risk of underperforming the index over time. The Fund generally holds fewer stocks than the index, and may hold securities that are not in the index.

Columbia Federal Securities Fund, Class Z (Federal Securities Fund)

Federal Securities Fund seeks as high a level of current income and total return as is consistent with prudent risk.

Under normal market conditions, Federal Securities Fund invests at least 80% of its net assets (plus any borrowings for investment purposes) in U.S. government securities, including U.S. treasuries and securities of various U.S. government agencies and instrumentalities. Agency securities include mortgage-backed securities, which represent interests in pools of mortgages. Certain securities of U.S. government agencies and instrumentalities in which the Fund invests are neither issued nor guaranteed by the U.S. Treasury. Such securities may be supported by the ability to borrow from the U.S. Treasury or only by the credit of the issuing agency or

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The Fund

instrumentality, and, as a result, may be subject to greater issuer risk than securities issued or guaranteed by the U.S. Treasury. The Fund may also invest up to 20% of its assets in corporate bonds or mortgage- or asset-backed securities that are issued by private entities. These securities must be rated investment grade by Moody's Investors Service, Inc. (Moody's), Standard & Poor's Corporation (S&P) or Fitch, Inc. (Fitch). The Fund has wide flexibility to vary its allocation among different types of U.S. government securities and the securities of non-governmental issuers based on the investment adviser's judgment of which types of securities will outperform the others. In selecting investments for the Fund, the adviser considers a security's expected income together with its potential to rise or fall in price.

Federal Securities Fund generally maintains a duration of greater than three years and less than 10 years. As a result, the Fund's portfolio has market risks and an expected average life comparable to intermediate- to long-term bonds. The Fund's adviser may vary the Fund's duration depending on its forecast of interest rates and market conditions. For example, when interest rates are expected to increase, the adviser may shorten the duration, and vice versa.

Columbia Intermediate Bond Fund, Class Z (Intermediate Bond Fund)

Intermediate Bond Fund seeks its total return by pursuing current income and opportunities for capital appreciation.

As part of its investment strategy, Intermediate Bond Fund may buy and sell securities frequently. Such trading usually increases portfolio turnover rates, which usually increases the chance that the Fund will pay investors short-term capital gains (which are taxable at higher rates than long-term capital gains). Such trading may also result in higher brokerage commissions and other transaction costs and additional tax liability, which could reduce the Fund's returns.

Under normal circumstances, Intermediate Bond Fund invests at least 80% of its net assets (plus any borrowings for investment purposes) in bonds, including:

•  debt securities issued by the U.S. government, including U.S. treasury securities and agency securities (agency securities include certain mortgage-backed securities, which represent interests in pools of mortgages),

•  debt securities of corporations, and

•  mortgage-backed and asset-backed securities issued by private (non-governmental) entities.

Intermediate Bond Fund will invest at least 60% of its net assets in high-quality debt securities that are at the time of purchase:

•  rated at least A by S&P;

•  rated at least A by Moody's;

•  given a comparable rating by another nationally recognized rating agency; or

•  unrated securities that the Fund's adviser believes to be of comparable quality.

Intermediate Bond Fund may invest up to 20% of its net assets in lower-rated debt securities. These securities are sometimes referred to as "junk bonds" and are at the time of purchase:

•  rated below BBB by S&P;

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The Fund

•  rated below Baa by Moody's;

•  given a comparable rating by another nationally recognized rating agency; or

•  unrated securities that the Fund's adviser believes to be of comparable quality.

Normally, Intermediate Bond Fund expects to maintain a dollar-weighted average effective maturity of three to 10 years. The Fund seeks to achieve capital appreciation through purchasing bonds that increase in market value. In addition, to a limited extent, the Fund may seek capital appreciation by using hedging techniques such as futures and options.

Intermediate Bond Fund's adviser has wide flexibility to vary the allocation among different types of debt securities based on its judgment of which types of securities will outperform the others.

Columbia Conservative High Yield Fund, Class Z (High Yield Fund)

High Yield Fund seeks a high level of income, with capital appreciation as a secondary goal.

High Yield Fund pursues its objective by investing in non-investment-grade corporate debt securities, commonly referred to as "junk" or "high-yield" bonds. Normally, the Fund will invest at least 80% of its assets (plus any borrowings for investment purposes) in bonds rated Ba or B by Moody's or BB or B by S&P. No more than 10% of the Fund's assets will be invested in bonds rated Caa by Moody's or CCC by S&P, and no Fund assets will be invested in bonds below these grades. By focusing on higher quality junk bonds, the Fund seeks access to higher yielding bonds without assuming all the risk associated with the broader junk bond market.

PRINCIPAL INVESTMENT RISKS

The principal risks of investing in the Fund are described below. The value of an investment in the Fund is based primarily on the performance of the Portfolio Funds and the allocation of the Fund's assets among them. There are many circumstances (including additional risks that are not described here) which could prevent the Fund from achieving its investment goal. You may lose money by investing in the Fund.

Management risk. Management risk means that the adviser's investment decisions might produce losses or cause the Fund to underperform when compared to other funds with a similar investment goal. The Fund does not have the ability to affect how the portfolio managers of the Portfolio Funds manage those funds.

Market risk. Market risk means that security prices in a market, sector or industry may fall, reducing the value of your investment. Because of management and market risk, there is no guarantee that the Fund will achieve its investment goal or perform favorably among comparable funds.

Interest rate risk. Since the Fund may invest in bond Portfolio Funds, it is subject to interest rate risk. This is the risk of a change in the price of a bond when prevailing interest rates increase or decline. In general, if interest rates rise, bond prices fall, and if interest rates fall, bond prices rise. Changes in the values of bonds usually will not affect the amount of income the Fund receives from them but will affect the value of the Fund's shares. Interest rate risk is generally greater for bonds with longer maturities.

Issuer risk. Because a Portfolio Fund may invest in debt securities issued or supported by private entities, including corporate bonds and mortgage-backed and asset backed securities, the Fund is subject to issuer risk. Issuer risk is the possibility that changes in the financial condition of the issuer of a security, changes in general economic conditions or changes in economic conditions that affect the issuer may impact its actual or perceived

10

The Fund

willingness or ability to make timely payments of interest or principal. This could result in a decrease in the price of the security and in some cases a decrease in income.

Credit risk. Credit risk is the possibility that changes in the obligated entity's financial condition, changes in general economic conditions, or changes in economic conditions that affect the obligated entity, may impact the obligated entity's actual or perceived willingness or ability to make timely payments of interest or principal. This could result in a decrease in the price of the security and, in some cases, a decrease in income. Bonds that are backed by an issuer's taxing authority, including general obligation bonds, may be vulnerable to legal limits on a government's power to raise revenue or increase taxes. These bonds may depend for payment on legislative appropriation and/or aid from other governments. Other municipal bonds, known as revenue obligations, are payable from revenues earned by a particular project or other revenue source. So me revenue obligations are backed by private companies, some are asset-backed securities, such as bonds backed by mortgage payments, and some are for municipally owned utilities, such as water or sewer systems. Revenue obligations are subject to greater risk of default than general obligation bonds because investors can look only to the revenue generated by the project, assets, or private company backing the project, rather than to the taxing power of the state or local government issuer of the bonds.

Structure risk and prepayment risk. Structure risk is the risk that an event will occur (such as a security being prepaid or called) that alters the security's cash flows. Prepayment risk is a particular type of structure risk that is associated with investments in asset-backed and mortgage-backed securities. With respect to investments in mortgage-backed securities, prepayment risk is the possibility that, as prevailing interest rates fall, homeowners are more likely to refinance their home mortgages. When mortgages are refinanced, the principal on mortgage-backed securities is paid earlier than expected. In an environment of declining interest rates, asset-backed and mortgage-backed securities may offer less potential for gain than other debt securities. During periods of rising interest rates, asset-backed and mortgage-backed securities have a high risk of declining in price because the declining prepayment rates effectively increase the expected life of the security. In addition, the potential impact of prepayment on the price of an asset-backed and mortgage-backed security may be difficult to predict and result in greater volatility.

Lower-rated debt securities. Lower-rated debt securities, commonly referred to as "junk bonds," involve greater risk of loss due to credit deterioration and are less liquid, especially during periods of economic uncertainty or change, than higher-quality debt securities. Lower-rated debt securities generally have a higher risk that the issuer of the security may default and not make payment of interest or principal.

Medium-quality debt securities. Medium-quality debt securities, although considered investment grade, may have some speculative characteristics.

Equity risk. Since the Fund invests in equity Portfolio Funds, it is subject to equity risk. This is the risk that stock prices will fall over short or extended periods of time. Although the stock market has historically outperformed other asset classes over the long term, the stock market tends to move in cycles. Individual stock prices may fluctuate drastically from day to day and may underperform other asset classes over an extended period of time. Individual companies may report poor results or be negatively affected by industry and/or economic trends and developments. The prices of securities issued by such companies may suffer a decline in response. These price movements may result from factors affecting individual companies, industries or the securities market as a whole.

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The Fund

Value stocks. Value stocks are stocks of companies that may have experienced adverse business or industry developments or may be subject to special risks that have caused the stocks to be out of favor and, in the adviser's opinion, undervalued. If the adviser's assessment of a company's prospects is wrong, the price of the company's stock may fall, or may not approach the value the adviser has placed on it.

Growth stocks. Because some of the Portfolio Funds invest in growth stocks, the Fund is subject to the risk that growth stocks may be out of favor with investors for an extended period of time. Growth stocks are stocks of companies believed to have above-average potential for growth in revenue and earnings. Prices of growth stocks may be more sensitive to changes in current or expected earnings than the prices of other stocks. Growth stocks may not perform as well as value stocks or the stock market in general.

Market trends. The Fund is also subject to the risk that the adviser's decisions regarding asset classes and Portfolio Funds will not anticipate market trends successfully. For example, weighting Portfolio Funds that invest in common stocks too heavily during a stock market decline may result in a failure to preserve capital. Conversely, investing too heavily in Portfolio Funds that invest in bonds during a period of stock market appreciation may result in lower total return. Of course, the risks associated with investing in the Fund will vary depending upon how the assets are allocated among Portfolio Funds.

Management has no control over the portfolio managers or investment decisions of the Portfolio Funds. However, decisions made by the Portfolio Funds' managers will have a significant effect on a Fund's performance.

Affiliated fund risk. In managing the Fund, the portfolio manager will have authority to change the Portfolio Funds in which Thermostat invests or to change the percentage allocations among the stock funds or the bond funds. Since different Portfolio Funds pay different rates of management fees to CWAM or its affiliates, CWAM may have a conflict of interest selecting the Portfolio Funds or in determining the relative percentage allocations among Portfolio Funds.

Sector risk. Sector risk is inherent in the Portfolio Funds' investment strategies. Companies that are in different but closely related industries are sometimes described as being in the same broad economic sector. The values of stocks of different companies in a market sector may be similarly affected by particular economic or market events. Although the Fund does not intend to focus on any particular sector, at times the Portfolio Funds may have a large portion of their assets invested in a particular sector.

Foreign securities. Foreign securities are subject to special risks. Foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the dollar value of foreign securities denominated in foreign currencies and U.S. dollars, without a change in the intrinsic value of those securities. The liquidity of foreign securities may be more limited than that of domestic securities, which means that a Portfolio Fund may, at times, be unable to sell foreign securities at desirable prices. Brokerage commissions, custodial fees and other fees are generally higher for foreign investments. The Fund may have limited legal recourse in the event of default with respect to certain debt securities issued by foreign governments. In addition, foreign governments may impose withholding taxes that would reduce the amount of income and capital gai ns available to distribute to shareholders. Other risks include possible delays in the settlement of transactions or in the notification of income; less publicly available information about companies; the impact of political, social or diplomatic events; possible seizure, expropriation or nationalization of the company or its assets; and possible imposition of currency exchange controls.

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The Fund

Emerging markets. Investments in emerging markets are subject to additional risk. The risks of foreign investments are typically increased in less developed countries, which are sometimes referred to as emerging markets. For example, political and economic structures in these countries may be new and developing rapidly, which may cause instability. These countries are also more likely to experience high levels of inflation, deflation or currency devaluations, which could hurt their economies and securities markets.

Small- or mid-cap companies. Small- or mid-cap companies may be more susceptible to market downturns, and their prices could be more volatile than large-cap companies. These companies are more likely than larger companies to have limited product lines, operating histories, markets or financial resources. They may depend heavily on a small management team and may trade less frequently, may trade in smaller volumes and may fluctuate more sharply in price than stocks of larger companies. In addition, such companies may not be widely followed by the investment community, which can lower the demand for their stocks.

Futures risk. Core Fund may use futures contracts periodically to manage liquidity. There is a risk that this could result in losses, reduce returns, increase transaction costs or increase the Fund's volatility.

Derivatives risk. The use of derivatives presents risks different from, and possibly greater than, the risks associated with investing directly in traditional securities. Among the risks presented are market risk, credit risk, management risk and liquidity risk. The use of derivatives can lead to losses because of adverse movements in the price or value of the underlying asset, index or rate, which may be magnified by certain features of the derivatives. These risks are heightened when the portfolio manager uses derivatives to enhance a Fund's return or as a substitute for a position or security, rather than solely to hedge (or offset) the risk of a position or security held by the Fund. The success of management's derivatives strategies will depend on its ability to assess and predict the impact of market or economic developments on the underlying as set, index or rate and the derivative itself, without the benefit of observing the performance of the derivative under all possible market conditions. Liquidity risk exists when a security cannot be purchased or sold at the time desired, or cannot be purchased or sold without adversely affecting the price. The portfolio manager is not required to utilize derivatives to reduce risks.

Investing in the Master Portfolio. Marsico Growth Fund invests in the Master Portfolio, in which other mutual funds and eligible investors can buy shares. All investors in the Master Portfolio invest under the same terms and conditions as Marsico Growth Fund and pay a proportionate share of the Master Portfolio's expenses. Other feeder funds that invest in the Master Portfolio may have different share prices and returns than Marsico Growth Fund because different feeder funds typically have varying sales charges, and ongoing administrative and other expenses.

Convertible securities. Convertible securities are securities that can be converted into common stock, such as certain debt securities and preferred stock. Convertible securities are subject to the usual risks associated with fixed income investments, such as interest rate risk and credit risk. In addition, because they react to changes in the value of the equity securities into which they will convert, convertible securities are also subject to market risk.

Market timers. Because Acorn International invests predominantly in foreign securities, it may be particularly susceptible to market timers. Market timers generally attempt to take advantage of the way a fund prices its shares by trading based on market information they expect will lead to a change in the fund's net asset value on the next pricing day. Market timing activity may be disruptive to fund management and, since a market timer's profits are effectively paid directly out of the fund's assets, may negatively impact the investment returns of other shareholders. Although Acorn International has adopted certain policies and methods intended to identify and

13

The Fund

discourage frequent trading based on this strategy, it cannot ensure that all such activity can be identified or terminated.

Portfolio turnover. The Fund may buy and sell shares of the Portfolio Funds frequently. This may result in more realized income and greater income taxes, and could increase the transaction costs of the Portfolio Funds.

An investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PORTFOLIO HOLDINGS DISCLOSURE

A description of the Fund's policies and procedures with respect to the disclosure of its portfolio securities is available in the Fund's Statement of Additional Information (SAI), which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611.

The Fund posts its complete portfolio holdings at as of month-end www.columbiafunds.com approximately 30-40 calendar days after such month-end. Additionally, the Fund discloses its top 15 month-end portfolio holdings at www.columbiafunds.com on or about 15 calendar days following such month-end.

Once posted, the above information will remain available on the website until at least the date on which the Fund files a Form N-CSR or Form N-Q for the period that includes the date as of which the information is current.

PERFORMANCE HISTORY

The bar chart below shows the Fund's calendar-year total returns (before taxes) for its Class A shares, excluding sales charges. The performance table following the bar chart shows how the Fund's average annual total returns for Class A, B and C shares, including sales charges, compare with broad measures of market performance for one year and the life of the share class. The chart and table are intended to illustrate some of the risks of investing in the Fund by showing changes in the Fund's performance from year to year. All returns include the reinvestment of dividends and distributions. As with all mutual funds, past performance (before and after taxes) does not predict the Fund's future performance.

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The Fund

UNDERSTANDING PERFORMANCE

Calendar Year Total Returns show the Fund's Class A share performance for each completed calendar year since the Class commenced operations. Those returns include the effects of Fund expenses, but not the effects of sales charges paid directly by the shareholder. If sales charges were included, these returns would be lower.

Average Annual Total Returns are a measure of the Fund's average performance over the past one-year and the life of the share class. The table shows returns of each share class and includes the effects of both Fund expenses and current sales charges. Class B share returns do not reflect Class A share returns after conversion of Class B shares to Class A shares — see the section "Your Account — Sales Charges (Commissions)."

The Fund's returns are compared to the S&P 500 Index, its benchmark with respect to equity securities, the Lehman Brothers U.S. Credit Intermediate Bond Index, the intermediate component of the Lehman Brothers U.S. Credit Index, its benchmark with respect to debt securities, and the Lipper Flexible Portfolio Funds Index. The S&P 500 Index is a broad market-weighted average of 500 widely-held large capitalization U.S. stocks. The Lehman Brothers U.S. Credit Index includes publicly issued U.S. corporate and foreign debentures and secured notes that meet specified maturity, liquidity and quality requirements. The Lipper Flexible Portfolio Funds Index is an equal dollar-weighted index of the 30 largest mutual funds within the Flexible Portfolio fund classification, as defined by Lipper. Unlike the Fund, indices are not investments, do not incur fees, expenses or taxes, and are not professionally managed.

Calendar Year Total Returns (Class A)

For the periods shown in bar chart:
Best quarter: 4th quarter 2004, +5.75%
Worst quarter: 1st quarter 2005, -1.14%

After-tax returns are calculated using the highest historical individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on each investor's own tax situation and may differ from those shown. After-tax returns may not be relevant to investors who hold Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

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The Fund

Average Annual Total Returns — for periods ended December 31, 2006

Share Class	1 Year		Life of the Share Class(1)
Class A (%)
Return Before Taxes		4.20		10.57
Return After Taxes on Distributions		1.98		9.03
Return After Taxes on Distributions and Sale of Fund Shares		3.71		8.49
Class B (%)
Return Before Taxes		4.91		11.00
Return After Taxes on Distributions		2.80		9.67
Return After Taxes on Distributions and Sale of Fund Shares		4.24		9.01
Class C (%)
Return Before Taxes		8.72		11.47
Return After Taxes on Distributions		6.68		10.20
Return After Taxes on Distributions and Sale of Fund Shares		6.71		9.45
Indices
S&P 500 Index (%)		15.79		16.67	(2)
Lehman Brothers U.S. Credit Intermediate Bond Index (%)		4.49		3.84	(2)
Lipper Flexible Portfolio Funds Index (%)		12.77		14.12	(2)

(1)  The inception date for Class A, Class B and Class C shares is March 3, 2003.

(2)  Performance information is from March 3, 2003.

COMMISSIONS AND OTHER EXPENSES

Expenses are one of several factors to consider before you invest in a mutual fund. The tables below describe the commissions and other expenses you may pay when you buy, hold and sell shares of the Fund.

UNDERSTANDING EXPENSES

Sales Charges (Commissions) are paid directly by shareholders to Columbia Management Distributors, Inc., the Fund's distributor, who compensates your financial advisor.

Annual Fund Operating Expenses are paid by the Fund. They include management and administration fees, 12b-1 fees and other expenses that generally include, but are not limited to, transfer agency, custody, and legal fees as well as costs related to state registration and printing of Fund documents. The specific fees and expenses that make up the Fund's other expenses will vary from time to time and may include fees or expenses not described here.

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The Fund

Shareholder Fees (commissions paid directly from your investment)

	Class A			Class B		Class C
Maximum sales charge (load) on purchases (%) (as a percentage of the offering price)		5.75		None		None
Maximum deferred sales charge (load) on redemptions (%) (as a percentage of the lesser of purchase price or redemption price)		1.00	(1)		5.00		1.00
Redemption fee (%) (as a percentage of amount redeemed, if applicable) (as a percentage of amount redeemed, if applicable)	None(2)			None(2)		None(2)

(1)  This charge applies only to certain purchases of Class A shares bought without an initial sales charge that are sold within 12 months of purchase.

(2)  There is a $7.50 charge for wiring sale proceeds to your bank.

Annual Fund Operating Expenses (deducted from Fund assets)

	Class A			Class B			Class C
Management fees(1) (%)		0.10			0.10			0.10
Distribution and service (12b-1) fees(2) (%)		0.25			0.75			1.00
Other expenses(3) (%)		0.31			0.34			0.36
Total annual fund operating expenses (%)		0.66			1.19			1.46
Expense reimbursement (%)		(0.16	)		(0.19	)		(0.21	)
Net expense ratio(4) (%)		0.50			1.00			1.25
Acquired Fund (Portfolio Fund) fees and expenses(5) (%)		0.69			0.69			0.69
Net expense ratio including expenses of Portfolio Funds(6) (%)		1.19			1.69			1.94
Gross expense ratio including expenses of Portfolio Funds (%)		1.35			1.88			2.15

(1)  The Fund pays an investment advisory fee of 0.10%. In addition to the management fee, the Fund and the other funds of Columbia Acorn Trust (the "Trust") pay the adviser an administrative fee based on the average daily aggregate net assets of the Trust at the following annual rates: 0.05% of net assets up to $8 billion; 0.04% of the next $8 billion; and 0.03% of net assets in excess of $16 billion. Based on the Trust's average daily net assets as of December 31, 2006, the administrative fee would be at a rate of 0.04% and is included in "Other expenses."

(2)  The distribution and service (12b-1) fees for Class B shares have been restated to reflect a reduction of the distribution fee rate by 0.10%, effective August 1, 2006.

(3)  "Other expenses" have been restated to reflect contractual changes to the transfer agency fees paid by the Fund.

(4)  The Fund's adviser has contractually agreed to bear a portion of the Fund's expenses so that the Fund's ordinary operating expenses (excluding any distribution and service fees, interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies) do not exceed 0.25% annually of the average daily net assets for Class A, Class B and Class C shares through April 30, 2008. The adviser will have the right to recoup expense reimbursement payments made to the Fund through December 31, 2007. This will be accomplished by the payment of an expense reimbursement fee by the Fund to the adviser computed and paid monthly, with a limitation that immediately after such payment the Fund's ordinary operating expenses (excluding any distribution and service fees, interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies) will not exce ed 0.25% annually.

(5)  Represents fees and expenses associated with the Fund's investments in other investment companies.

(6)  Includes the fees and expenses incurred by the Fund directly and indirectly from the underlying Portfolio Funds in which the Fund invests. The ratios shown above are based on the average invested balance of the Portfolio Funds, based on the respective net expense ratios of the Portfolio Funds for their respective last annual or semiannual report. Based on this allocation, the Fund's estimated indirect annual expenses would have been 0.69%. The indirect expense ratio of the Fund may be higher or lower depending on the portion of the Fund's assets allocated to each Portfolio Fund from time to time. As a result, the amount shown is higher than the ratio of expenses to average net assets included in the section entitled "Financial Highlights," which reflects only those expenses paid directly by the Fund.

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The Fund

Example Expenses help you compare the cost of investing in the Fund to the cost of investing in other mutual funds. The table does not take into account any expense reduction arrangements discussed in the footnotes to the Annual Fund Operating Expenses table. It uses the following hypothetical conditions:

•  $10,000 initial investment

•  5% total return for each year

•  Fund operating expenses remain the same

•  Reinvestment of all dividends and distributions

•  Class B shares convert to Class A shares after eight years

Example Expenses for a $10,000 investment⁽¹⁾ (your actual costs may be higher or lower)

Class		1 Year		3 Years		5 years		10 years
Class A:		$	689	$	963	$	1,257	$	2,092
Class B:	did not sell your shares	$	172	$	572	$	999	$	2,047
	sold all your shares
	at the end of the period	$	672	$	872	$	1,199	$	2,047
Class C:	did not sell your shares	$	197	$	653	$	1,135	$	2,466
	sold all your shares at
	the end of the period	$	297	$	653	$	1,135	$	2,466

(1)  Includes the fees and expenses incurred by the Fund directly and indirectly from the underlying Portfolio Funds in which the Fund invests. The example expenses for the one-year period reflect the contractual cap on expenses referred to in footnote (4), but this arrangement is not reflected in the example expenses for the second and third years of the three-year period, the second through fifth years of the five year period, or the second through tenth years of the ten year period.

See Appendix B for additional hypothetical investment and expense information.

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CHOOSING A SHARE CLASS

The Fund offers three classes of shares in this prospectus — Class A, Class B and Class C. Each of those share classes has its own commission and expense structure that affects the investment return of that class. Determining which share class is best for you depends on various factors, including the amount you are investing, how long you expect to hold your investment and your personal situation.

You should consult with your financial advisor before deciding which share class is most appropriate for you. The following considerations should be part of your assessment:

•  You will pay a commission if you buy Class A, B or C shares, either at the time of investment or redemption, or through ongoing distribution commission payments (Rule 12b-1 fees) made from your investment over time, or both.

•  Class A shares require an up-front commission payment, but pay lower ongoing Rule 12b-1 fees than Class B and Class C shares. Class B and Class C shares have no up-front commission paid by the shareholder but pay higher ongoing commissions (Rule 12b-1 fees), and a deferred commission is imposed on a redemption of Class B shares within six years after purchase, and a deferred commission is imposed on a redemption of Class C shares within one year of purchase. The differential between classes will vary depending on the actual investment return for any given period.

•  Class A shares can be more advantageous to an investor who intends to hold the shares for several years and invests an amount large enough to qualify for a reduced rate of initial sales commission, taking into account the commissions that investor may pay when redeeming shares of other classes. To project whether Class A shares might be more advantageous to you, you should consider, among other factors, the time period you intend to hold the shares, your initial sales commission and a comparison of the total annual expenses of Class A shares to the expenses of other share classes. Class A shares pay an ongoing annual commission (Rule 12b-1 fee) of up to 0.25% of the average value of the shares.

•  Class B shares pay an ongoing annual commission (Rule 12b-1 fee) of up to 0.75% of the average value of the shares and automatically convert to Class A shares after eight years. A Class B shareholder of the Fund whose account has a value of less than $50,000 (including for this purpose the combined value of all eligible accounts maintained by that shareholder that would be used to determine eligibility for reduced sales charges on Class A shares) may purchase additional Class B shares of the Fund to increase the account value up to a maximum of $49,999; any additional investment by the shareholder in that Fund will be invested in Class A shares of the Fund, without regard to the normal investment minimum for Class A shares, but will be subject to the applicable Class A shares up-front commission.

•  Class C shares are generally more advantageous to an investor who intends to hold shares for only a few years. Class C shares pay an ongoing annual commission (Rule 12b-1 fee) of up to 1.00% of the average value of the shares.

•  If you invest $1 million or more, you can purchase Class A shares but not Class C shares.

The Fund also offers an additional class of shares, Class Z shares, exclusively to certain institutional and other eligible investors. Class Z shares are made available through a separate prospectus provided to eligible institutional and other investors.

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HOW TO BUY SHARES

Your financial advisor can help you establish an appropriate investment portfolio, buy shares and monitor your investments. When the Fund receives your purchase request in "good form," your shares will be bought at the next calculated public offering price. "Good form" means that the Fund's transfer agent has all information and documentation it deems necessary to effect your order. For example "good form" may mean that you have properly placed your order with your financial advisor or the Fund's transfer agent has received your completed application, including all necessary signatures. The Fund reserves the right to refuse a purchase order for any reason, including if the Fund believes that doing so would be in the best interest of the Fund and its shareholders. The USA PATRIOT Act may require us to obtain certain personal information from you that we will use to verify your identity. If you do not provide the information, we m ay not be able to open your account. If we are unable to verify your customer information, we reserve the right to close your account or take such other steps as we deem reasonable.

INVESTMENT MINIMUMS

The minimum initial investment for Class A, Class B and Class C shares generally is $2,500. The investment minimum is applied at the class level. For individual retirement plans (including traditional IRAs, Roth IRAs and Coverdell Education Savings Accounts) and non-omnibus group retirement accounts, the minimum initial investment is $1,000. For non-omnibus group retirement plans, the investment minimum is determined based on the plan's investment rather than on the separate investments of its individual participants. For investors establishing an automatic investment plan, the minimum initial investment is $50. There is no minimum initial investment for omnibus accounts or wrap accounts.

The minimum investment for additional purchases of Class A, Class B and Class C shares is $50 for all investors.

The Fund reserves the right to change these investment minimums. The Fund also reserves the right to refuse a purchase order for any reason, including if it believes that doing so would be in the best interest of the Fund and its shareholders. In addition, pursuant to the Trust's Agreement and Declaration of Trust, the Fund reserves the right to redeem your shares if your account falls below the minimum investment restrictions.

Please see the SAI for more details on investment minimums.

Outlined below are the various options for buying shares:

Method	Instructions
Through your financial advisor	Your financial advisor can help you establish your account and buy Fund shares on your behalf. To receive the current trading day's price, your financial advisor must receive your request prior to the close of regular trading on the New York Stock Exchange (NYSE), usually 4:00 p.m. Eastern time. Your financial advisor may charge you fees for executing the purchase for you.
By check (new account)	For new accounts, send a completed application and check made payable to the Fund to the transfer agent, Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By check (existing account)	For existing accounts, fill out and return the additional investment stub included in your account statement, or send a letter of instruction including your name, the Fund's share class and account number with a check made payable to the Fund to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By exchange	You or your financial advisor may acquire Fund shares for your account by exchanging shares you own in a different fund distributed by Columbia Management Distributors, Inc. for shares of the same class (and, in some cases, certain other classes) of the Fund at no additional cost. An exchange to another fund may incur a sales charge if the original purchase was not assessed a sales charge. To exchange by telephone, call 1-800-422-3737. Please see "How to Exchange Shares" for more information.

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Method	Instructions
By wire	You may purchase Fund shares by wiring money from your bank account to your Fund account. To wire funds to your Fund account, call 1-800-422-3737 for wiring instructions.
By electronic funds transfer	You may purchase Fund shares by electronically transferring money from your bank account to your Fund transfer by calling 1-800-422-3737. An electronic funds transfer may take up to two business days to settle and be considered in "good form." You must set up this feature prior to your telephone request. Be sure to complete the appropriate section of the application for this feature.
Automatic investment plan	You may make monthly or quarterly investments automatically ($50 minimum) from your bank account to your Fund account. You may select a pre-authorized amount to be sent via electronic funds transfer. Be sure to complete the appropriate section of the application for this feature.
Automated dollar costaveraging	You may purchase Fund shares for your account by exchanging $100 or more each month from another fund for shares of the same class of the Fund at no additional cost. Exchanges will continue so long as your fund balance is sufficient to complete the transfers. You may terminate your program or change the amount of the exchange (subject to the $100 minimum) by calling 1-800-345-6611. There may be an additional sales charge if exchanging from a money market fund. Be sure to complete the appropriate section of the account application for this feature.
By dividend diversification	You may automatically invest dividends distributed by another fund into the same class of Fund shares (and, in some cases, certain other classes) at no additional sales charge. There may be an additional sales charge if automatically investing dividends from a money market fund. To invest your other dividends in the Fund, call 1-800-345-6611.
Through the internet	You may purchase Fund shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet purchases. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1 800-345-6611.

SALES CHARGES (COMMISSIONS)

You may be subject to an initial sales charge when you purchase, or a contingent deferred sales charge (CDSC) when you sell, shares of the Fund. These sales charges are described below. In certain circumstances, the sales charge may be reduced or waived, as described below and in the SAI.

Rule 12b-1 Plan The Fund has adopted a plan under Rule 12b-1 under the Investment Company Act that permits it to pay its distributor ongoing sales and marketing fees (commissions) to support the sale and distribution of Class A, B and C shares and certain services provided to you by your financial advisor, and your financial advisor may receive all or a portion of those fees attributable to your shares. The annual fee, as a percentage of the value of the shares, is normally 0.25% for Class A, 0.75% for Class B and 1.00% for Class C shares. These fees are paid out of the assets of these share classes. Over time, these fees reduce the return on your investment. Class B shares automatically convert to Class A shares after eight years, eliminating a portion of the Rule 12b-1 fee thereafter.

Financial Intermediary Payments

The Fund's distributor, investment adviser or their affiliates may make payments, from their own resources, to certain financial intermediaries, including other Bank of America affiliates, for marketing support services. For purposes of this section the term "financial intermediary" includes any broker, dealer, bank, bank trust department, registered investment adviser, financial planner, retirement plan or other third-party administrator and any other institution having a selling, services or any similar agreement with the Fund's distributor, investment adviser or one of their affiliates. These payments are generally based upon one or more of the following factors: average net assets of the mutual funds distributed by the Fund's distributor attributable to that financial intermediary, gross sales of the mutual funds distributed by the Fund's distributor attributable to that financial intermediary, reimbursement of ticket charge s (fees that a financial intermediary firm charges its representatives for effecting transactions in fund shares) or a negotiated lump sum payment.

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While the financial arrangements may vary for each financial intermediary, the support payments to any one financial intermediary are generally expected to be between 0.05% and 0.35% on an annual basis for payments based on average net assets of the Fund attributable to the financial intermediary, and between 0.10% and 0.25% on an annual basis for firms receiving a payment based on gross sales of the Fund attributable to the financial intermediary. The Fund's distributor, investment adviser or their affiliates may make payments in materially larger amounts or on a basis materially different from those described above when dealing with other affiliates of Bank of America. Such increased payments to the other Bank of America affiliate may enable the other Bank of America affiliate to offset credits that it may provide to its customers in order to avoid having such customers pay fees to multiple Bank of America entities in connecti on with the customer's investment in the Fund.

Payments also may be made to certain financial intermediaries, including other Bank of America affiliates, that provide investor services to retirement plans and other investment programs to compensate financial intermediaries for services they provide to such programs, including, but not limited to, sub-accounting, sub-transfer agency, similar shareholder or participant recordkeeping, shareholder or participant reporting, or shareholder or participant transaction processing. These payments for investor servicing support vary by financial intermediary but generally are not expected, with certain limited exceptions, to exceed 0.35% of the total Fund assets for Class A, B and C shares in the program on an annual basis.

The Trust's Board of Trustees has authorized the Fund to pay to any intermediary up to 0.05% of the average aggregate value of Fund shares in the intermediary's program on an annual basis for providing investor services. Charges of an intermediary in excess of that paid by the Fund will be borne by the Fund's distributor or its affiliates.

The Fund's distributor, investment adviser or their affiliates may make other payments or allow promotional incentives to financial intermediaries to the extent permitted by the rules of Securities and Exchange Commission, the National Association of Securities Dealers and by other applicable laws and regulations.

Amounts paid by the Fund's distributor, investment adviser or their affiliates are paid out of the distributor's, investment adviser's or their affiliates' own resources and do not increase the amount paid by you or the Fund. You can find further details about the payments made by the Fund's distributor, investment adviser or their affiliates and the services provided by financial intermediaries as well as a list of the financial intermediaries to which the Fund's distributor, investment adviser or their affiliates have agreed to make marketing support payments in the Fund's SAI, which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611. Your financial intermediary may charge you fees or commissions in addition to those disclosed in this prospectus. You can ask y our financial intermediary for information about any payments it receives from the Fund's distributor, investment adviser and their affiliates and any services your financial intermediary provides, as well as fees and/or commissions it charges. In addition, depending on the financial arrangement in place at any particular time, a financial intermediary and its financial consultants also may have a financial incentive for recommending a particular fund or share class over others. You should consult with your financial adviser and review carefully any disclosure by the financial intermediary as to compensation received by your financial adviser.

Class A shares Your purchases of Class A shares are made at the public offering price for these shares. This price includes a sales charge that is based on the amount of your initial investment when you open your account. The sales charge you pay on an additional investment is based on the total amount of your purchase and the current value of your account. Shares you purchase with reinvested dividends or other distributions are not subject to a sales charge. A

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portion of the sales charge is paid as a commission to your financial advisor on the sale of Class A shares. The amount of the sales charge differs depending on the amount you invest as shown in the table below.

Class A Sales Charges

	Sales Charges as % of:				% of offering price
Amount of purchase	offering price		net amount invested		retained by your financial advisor
Less than $50,000		5.75		6.10		5.00
$50,000 to less than $100,000		4.50		4.71		3.75
$100,000 to less than $250,000		3.50		3.63		2.75
$250,000 to less than $500,000		2.50		2.56		2.00
$500,000 to less than $1,000,000		2.00		2.04		1.75
$1,000,000 or more		0.00		0.00		0.00

In addition to the initial sales charge paid to your financial advisor and distributor, a 0.25% annual commission is paid to your financial advisor over the life of your investment out of your Fund assets as a 12b-1 fee.

The Fund's distributor may also pay additional compensation to financial advisors as an incentive for promoting the sale of shares of funds that it distributes.

Class A shares bought without an initial sales charge in accounts aggregating up to $50 million at the time of purchase are subject to a 1.00% CDSC if the shares are sold within 12 months of the time of purchase. Subsequent Class A share purchases that bring your account value above $1 million (but less than $50 million) are subject to a CDSC if redeemed within 12 months of the date of purchase. The 12-month period begins on the first day of the month in which the purchase was made. The CDSC does not apply to retirement plans purchasing shares through a fee-based program.

For Class A share purchases of $1 million or more, financial advisors receive a cumulative commission from the distributor as follows:

Purchases Over $1 Million

Amount purchased	Commission %
$1 million to less than $3 million		1.00
$3 million to less than $50 million		0.50
$50 million or more		0.25

For group retirement plans, financial advisors are eligible to receive a 1.00% commission from the distributor on purchases, including those in amounts less than $1 million, that are coded as commission eligible trades. In determining the commission payable to a financial advisor in the above table, the breakpoint discount policies described in "Reduced Sales Charges (Commissions) for Larger Investments," on page 24, shall apply.

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UNDERSTANDING CONTINGENT DEFERRED SALES CHARGES (COMMISSIONS)

Certain investments in Class A, B and C shares are subject to a CDSC, a sales charge applied at the time you sell your shares. You will pay the CDSC only on shares you sell within a certain amount of time after purchase. The CDSC generally declines each year until there is no charge for selling shares. The CDSC is applied to the net asset value at the time of purchase or sale, whichever is lower. For purposes of calculating the CDSC, the start of the holding period is the first day of the month in which the purchase was made. Shares you purchase with reinvested dividends or other distributions are not subject to a CDSC. When you place an order to sell shares, the Fund will automatically sell first those shares not subject to a CDSC and then those you have held the longest.

Reduced Sales Charges (Commissions) for Larger Investments.

A.  What are the principal ways to obtain a breakpoint discount?

There are two principal ways you may pay a lower sales charge (often referred to as "breakpoint discounts") when purchasing Class A shares of the Fund and other funds in the Columbia family of funds.

Rights of Accumulation The value of eligible accounts maintained by you and each member of your immediate family may be combined with the value of your current purchase to reach a sales charge discount level (according to the chart on the previous page) and to obtain the lower sales charge for your current purchase. To calculate the combined value of the accounts, the Fund will use the shares' current public offering price.

Statement of Intent You also may pay a lower sales charge when purchasing Class A shares by signing a Statement of Intent. By doing so, you would be able to pay the lower sales charge on all purchases made under the Statement of Intent within 13 months. As described in the chart on the previous page, the first breakpoint discount will be applied when total purchases reach $50,000. If your Statement of Intent purchases are not completed within 13 months, you will be charged the applicable sales charge on the amount you had invested to that date. To calculate the total value of your Statement of Intent purchases, the Fund will use the historic cost (i.e. dollars invested) of the shares held in each eligible account. You must retain all records necessary to substantiate historic costs because the Fund and your financial intermediary may not maintain this information.

B.  What accounts are eligible for breakpoint discounts?

The types of eligible accounts that may be aggregated to obtain one or both of the breakpoint discounts described above include:

•  Individual accounts

•  Joint accounts

•  Certain IRA accounts

•  Certain trusts

•  UTMA/UGMA accounts

For the purposes of obtaining a breakpoint discount, members of your "immediate family" include your spouse, parent, stepparent, legal guardian, child, stepchild, father in-law and mother in-law. Eligible accounts include those registered in the name of your dealer or other financial intermediary through which you own Columbia

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fund shares. An account is not eligible to the extent it holds an institutional class of shares of a Columbia money market fund or Class R shares of any Columbia fund. The value of your investment in a non-institutional class of a Columbia money market fund held in an eligible account may be aggregated with your investments in other funds in the Columbia family of funds to obtain a breakpoint discount through a Right of Accumulation. Non-institutional class investments in Columbia money market funds may also be included in the aggregation for a Statement of Intent for shares that have been charged a commission.

C.  How do I obtain a breakpoint discount?

The steps necessary to obtain a breakpoint discount depend on how your account is maintained with the Columbia family of funds. To obtain any of the above breakpoint discounts, you must notify your financial advisor at the time you purchase shares of the existence of each eligible account maintained by you or your immediate family. It is the sole responsibility of your financial advisor to ensure that you receive discounts for which you are eligible, and the Fund is not responsible for a financial advisor's failure to apply the eligible discount to your account. You may be asked by the Fund or your financial advisor for account statements or other records to verify your discount eligibility, including, where applicable, records for accounts opened with a different financial advisor and records of accounts established by members of your immediate family. If you own shares exclusively through an account maintained with the Fund's transfer agent, Columbia Management Services, Inc., you will need to provide the foregoing information to a Columbia Management Services, Inc. representative at the time you purchase shares.

D.  How can I obtain more information about breakpoint discounts?

Certain investors, including affiliates of the Fund, broker/dealers and their affiliates, investors in wrap-fee programs through fee-based advisers or certain retirement plans, certain shareholders of funds that were reorganized into other Columbia funds, and investors using the proceeds of redemptions of Fund shares or of certain Bank of America trust or similar accounts, may purchase shares at a reduced sales charge or net asset value, which is the value of a fund share excluding any sales charges. CDSCs may also be waived for redemptions under a systematic withdrawal program, in connection with the death or post-purchase disability of a shareholder, certain medical expenses, charitable gifts, involuntary and tax-related redemptions, or when the selling broker/dealer has agreed to waive or return its commission. Restrictions may apply to certain accounts and certain transactions. Further information regarding these discounts m ay be found in the Fund's SAI, which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611.

Class B shares Your purchases of Class B shares are at Class B's net asset value. Purchases in Class B shares may not result in the account holding $50,000 or more of Class B shares (including for this purpose the combined value of all eligible accounts maintained by you that would be used to determine eligibility for reduced sales charges on Class A shares). In the event that an existing Class B shareholder seeks to add funds to such an account so that the balance would be in excess of $49,999, the amount in excess may be invested in Class A shares without the imposition of the minimum investment requirement for Class A shares. Such purchases of Class A shares will be subject to the applicable sales load imposed on such purchases. See "Class A Sales Charges" on page 23.

Class B shares have no front-end sales charge, but they do carry a CDSC that is imposed only on shares sold within six years of purchase. The CDSC declines over the six years and disappears in the seventh year. The distributor pays your financial advisor an up-front commission on sales of Class B shares as described in the

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chart below. In addition, Class B shares bear ongoing service and distribution fees that are higher than those borne by Class A shares.

Purchases of less than $50,000:

Class B Sales Charges

Holding period after purchase	% deducted when shares are sold(1)
Through first year		5.00
Through second year		4.00
Through third year		3.00
Through fourth year		3.00
Through fifth year		2.00
Through sixth year		1.00
Longer than six years		0.00

(1)  Applied to the net asset value at the time of purchase or sale, whichever is lower.

In addition, from the annual fee of 0.75% of the value of your shares paid out of your Fund assets as Rule 12b-1 fees, the distributor receives 0.50% of the value of the shares for each of the first eight years, or an aggregate 4.00% over eight years, which will offset the commission it paid to your financial advisor. Your financial advisor is paid the remaining 0.25% as an ongoing commission for the life of your investment.

The conversion of Class B shares to Class A shares occurs automatically eight years after purchase.

Class C shares Your purchases of Class C shares are at Class C's net asset value. Although Class C shares have no front-end sales charge, they carry a CDSC of 1.00% that is applied to shares sold within the first year after they are purchased. After holding shares for one year, you may sell them at any time without paying a CDSC. The distributor pays your financial advisor an up-front commission of 1.00% on your purchase of Class C shares, for which the distributor is repaid from the ongoing annual fee of 1.00% of the value of your shares paid out of your Fund assets as Rule 12b-1 fees, which is higher than the Rule 12b-1 fees borne by Class A and Class B shares.

Class C Sales Charges

Holding period after purchase	% deducted when shares are sold(1)
Through one year		1.00
Longer than one year		0.00

(1)  Applied to the net asset value at the time of purchase or sale, whichever is lower.

A 1.00% annual commission is paid to your financial advisor and the distributor over the life of your investment out of your Fund assets.

HOW TO EXCHANGE SHARES

You may exchange your shares for shares of the same share class (and in some cases, certain other classes) of another fund distributed by Columbia Management Distributors, Inc. at net asset value. If your shares are subject to a CDSC, you will not be charged a CDSC upon the exchange. However, when you sell the shares acquired through the exchange, the shares sold may be subject to a CDSC, depending upon when you originally purchased

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the shares you are exchanging. For purposes of computing the CDSC, the length of time you have owned your shares will be computed from the date of your original purchase and the applicable CDSC will be the CDSC of the original fund. Shareholders of Columbia Acorn Funds that qualify to purchase Class A shares at net asset value may exchange their Class A shares for Class Z shares of another fund distributed by Columbia Management Distributors, Inc. (see the SAI for a description of these situations). Unless your account is part of a tax-deferred retirement plan, an exchange is a taxable event, and you may realize a gain or a loss for tax purposes. The Fund may terminate your exchange privilege if the adviser determines that your exchange activity is likely to adversely impact its ability to manage the Fund. See "Fund Policy on Trading of Fund Shares" for the Fund's policy. To exchange by telephone, call 1-800-422-3737. Please hav e your account and taxpayer identification numbers available when calling.

You also may exchange your shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet exchanges. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

HOW TO SELL SHARES

Your financial advisor can help you determine if and when you should sell your shares. You may sell shares of the Fund on any regular business day that the NYSE is open.

When the Fund receives your sales request in "good form," shares will be sold at the next calculated net asset value. "Good form" means that the Fund's transfer agent has all information and documentation it deems necessary to effect your order. For example, when selling shares by letter of instruction, "good form" means (i) your letter has complete instructions, the proper signatures and Medallion Signature Guarantees, (ii) if applicable, you have included any certificates for shares to be sold, and (iii) any other required documents are attached. For additional documents required for sales by corporations, agents, fiduciaries, surviving joint owners and other legal entities, please call 1-800-345-6611. Retirement plan accounts have special requirements; please call 1-800-799-7526 for more information.

The Fund will generally send proceeds from the sale to you within seven days (usually on the next business day after your request is received in "good form"). However, if you purchased your shares by check, the Fund may delay sending the proceeds from the sale of your shares for up to 10 days after your purchase to protect against checks that are returned. No interest will be paid on uncashed redemption checks. Redemption proceeds may be paid in securities rather than cash, under certain circumstances. For more information, see the paragraph "Non-Cash Redemptions" under the section "How to Sell Shares" in the SAI.

During any 90-day period for any one shareholder, the Fund is obligated to redeem shares solely in cash up to the lesser of $250,000 or 1% of the Fund's net assets. Redemptions in excess of these limits will normally be paid in cash, but may be paid wholly or partly by an in-kind distribution of securities.

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Outlined below are the various options for selling shares:

Method	Instructions
Through your financial advisor	You may call your financial advisor to place your sell order. To receive the current trading day's price, your financial advisor must receive your request prior to the close of regular trading on the NYSE, usually 4:00 p.m. Eastern time. Your financial advisor may charge you fees for executing a redemption for you.
By exchange	You or your financial advisor may sell Fund shares by exchanging from the Fund into the same share class (and, in some cases, certain other classes) of another fund distributed by Columbia Management Distributors, Inc. at no additional cost. To exchange by telephone, call 1-800-422-3737.
By telephone	You or your financial advisor may sell Fund shares by telephone and request that a check be sent to your address of record by calling 1-800-422-3737, unless you have notified the Fund of an address change within the previous 30 days. The dollar limit for telephone sales is $100,000 in a 30-day period. You do not need to set up this feature in advance of your call. Certain restrictions apply to retirement accounts. For details, call 1-800-799-7526.
By mail	You may send a signed letter of instruction or, if applicable, stock power form along with any share certificates to be sold to the address below. In your letter of instruction, note the Fund's name, share class, account number, and the dollar value or number of shares you wish to sell. All account owners must sign the letter. Signatures must be guaranteed by either a bank, a member firm of a national stock exchange or another eligible guarantor that participates in the Medallion Signature Guarantee Program for amounts over $100,000 or for alternate payee or mailing instructions. Additional documentation is required for sales by corporations, agents, fiduciaries, surviving joint owners and individual retirement account owners. For details, call 1-800-345-6611. Mail your letter of instruction to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By wire	You may sell Fund shares and request that the proceeds be wired to your bank. You must set up this feature prior to your request. Be sure to complete the appropriate section of the account application for this feature. Generally, the value of your redemption must be at least equal to $500 in order to have the sale proceeds wired to your bank. There is a $7.50 charge for wiring sale proceeds to your bank. (The transfer agent may waive this fee for omnibus and nominee accounts.) Your bank may charge additional fees for such wire transfer.
By systematic withdrawal plan	You may automatically sell a specified dollar amount or percentage of your account on a monthly, quarterly or semiannual basis and have the proceeds sent to you if your account balance is at least $5,000. The $5,000 minimum account balance requirement has been waived for wrap accounts. This feature is not available if you hold your shares in certificate form. All dividend and capital gains distributions must be reinvested. Be sure to complete the appropriate section of the account application for this feature.
By electronic funds transfer	You may sell Fund shares and request that the proceeds be electronically transferred to your bank. Proceeds may take up to two business days to be received by your bank. You must set up this feature prior to your request. Be sure to complete the appropriate section of the account application for this feature.
Through the internet	You may sell Fund shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet redemptions. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1 800-345-6611.

FUND POLICY ON TRADING OF FUND SHARES

The interests of the Fund's long-term shareholders may be adversely affected by certain short-term trading activity by Fund shareholders. Such short-term trading activity, when excessive, has the potential to interfere with efficient portfolio management, generate transaction and other costs, dilute the value of Fund shares held by long-term shareholders and have other adverse effects on the Fund. This type of excessive short-term trading activity is referred to herein as "market timing." For purposes of this section, the "Columbia Funds" are the Columbia, Columbia Acorn Trust and Wanger Advisors Trust families of mutual funds.The Columbia Funds are not intended as vehicles for market timing. The Board of Trustees of the Fund has adopted the policies and procedures set forth below with respect to frequent trading of the Fund's shares.

The Fund, directly and through its agents, takes various steps designed to deter and curtail market timing. For example, if the Fund detects that any shareholder has conducted two "round trips" (as defined below) in any

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28-day period, except as noted below with respect to orders received through omnibus accounts, the Fund will reject the shareholder's future purchase orders, including exchange purchase orders, involving any Columbia fund (other than a money market fund). In addition, if the Fund determines that any person, group or account has engaged in any type of market timing activity (independent of the two-round-trip limit), the Fund may, in its discretion, reject future purchase orders by the person, group or account, including exchange purchase orders, involving the same or any other Columbia fund, and also retains the right to modify these market timing policies at any time without prior notice.

The rights of shareholders to redeem shares of the Fund are not affected by any of the limits mentioned above. However, certain funds (other than the Fund) impose a redemption fee on the proceeds of shares that are redeemed or exchanged within 60 days of their purchase.

For these purposes, a "round trip" is a purchase by any means into a Columbia fund followed by a redemption, of any amount, by any means out of the same Columbia fund. Under this definition, an exchange into the Fund followed by an exchange out of the Fund is treated as a single round trip. Also for these purposes, where known, accounts under common ownership or control generally will be counted together. Accounts maintained or managed by a common intermediary, such as an adviser, selling agent or trust department, generally will not be considered to be under common ownership or control.

Purchases, redemptions and exchanges made through the Columbia Funds' Automatic Investment Plan, Systematic Withdrawal Plan or similar automated plans are not subject to the two-round-trip limit. Purchases, redemptions and exchanges made by Thermostat Fund are also not subject to the two round-trip limit. The two-round-trip limit may be modified for, or may not be applied to, accounts held by certain retirement plans to conform to plan limits, considerations relating to the Employee Retirement Income Security Act of 1974 or regulations of the Department of Labor, and for certain asset allocation or wrap programs.

The practices and policies described above are intended to deter and curtail market timing in the Fund. However, there can be no assurance that these policies, individually or collectively, will be totally effective in this regard because of various factors. In particular, a substantial portion of purchase, redemption and exchange orders are received through omnibus accounts. Omnibus accounts, in which shares are held in the name of an intermediary on behalf of multiple beneficial owners, are a common form of holding shares among financial intermediaries and retirement plans. The Fund typically is not able to identify trading by a particular beneficial owner through an omnibus account, which may make it difficult or impossible to determine if a particular account is engaged in market timing. Consequently, there is the risk that the Fund may not be able to identify, deter or curtail certain market timing that occurs in the Fund, which may result in certain shareholders being able to market time the Fund while the shareholders in the Fund bear the burden of such activities.

Certain financial intermediaries (including certain retirement plan service providers whose clients include, among others, various retirement plans sponsored by Bank of America and its affiliates for the benefit of its employees (the "Bank of America retirement plan service providers")) have different policies regarding monitoring and restricting market timing in the underlying beneficial owner accounts that they maintain through an omnibus account that may be more or less restrictive than the Fund practices discussed above. In particular, the Bank of America retirement plan service providers permit the reinstatement of future purchase orders for shares of the Fund following various suspension periods. If an intermediary does not enforce the Fund's policy, the intermediary must either provide data transparency to Columbia Management or Columbia Management must

29

Your Account

determine that the intermediary's policy taken in its entirety provides protections to Fund shareholders that are generally commensurate with the Fund's policy.

The Fund seeks to act in a manner that it believes is consistent with the best interests of Fund shareholders in making any judgments regarding market timing. Neither the Fund nor its agents shall be held liable for any loss resulting from rejected purchase orders or exchanges.

OTHER INFORMATION ABOUT YOUR ACCOUNT

How the Fund's Share Price is Determined The price of each class of its Fund's shares is based on its net asset value. The net asset value is determined at the close of regular trading on the NYSE, usually 4:00 p.m. Eastern time, on each business day that the NYSE is open for trading (typically Monday through Friday). Net asset value is not determined on days on which the NYSE is closed for trading.

When you request a transaction, it will be processed at the net asset value per share (plus any applicable sales charges) next determined after your request is received in "good form" by the distributor. In most cases, in order to receive that day's price, the distributor must receive your order before that day's transactions are processed. If you request a transaction through your financial advisor, your financial advisor must receive your order by the close of trading on the NYSE to receive that day's price.

The Fund determines its net asset value for each share class by dividing each class's total net assets by the number of that class's outstanding shares. In determining the net asset value, the Fund must determine the value of each security in its portfolio at the close of each trading day. Because some of the Portfolio Funds hold securities that are traded on foreign exchanges, the value of the Portfolio Funds' securities may change on days when shareholders will not be able to buy or sell Fund shares. This will affect the Fund's net asset value on the day it is next determined. Securities for which market quotations are available are valued each day at the current market value. However, where market quotations are unavailable, or when the Portfolio Fund's adviser believes that subsequent events have made them unreliable, the Fund may use other data to determine the fair value of the securities.

The Fund has retained an independent statistical fair value pricing service to assist in the fair valuation process for securities principally traded in a foreign market in order to adjust for possible changes in value that may occur between the close of the foreign exchange and the time at which Fund shares are priced. The use of an independent fair value pricing service is intended to and may decrease the opportunities for time zone arbitrage transactions. There can be no assurance that the use of an independent fair value pricing service will successfully decrease arbitrage opportunities. If a security is valued at a "fair value," that value may be different from the last quoted market price for the security.

You can find the daily prices of some share classes for the Fund in most major daily newspapers under the heading of "Columbia." You can find daily prices for all share classes by visiting www.columbiafunds.com.

Share Certificates Share certificates are not available for any class of shares offered by the Fund. If you currently hold previously issued share certificates, you will not be able to sell your shares until you have returned your share certificates to the transfer agent.

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Your Account

Dividends, Distributions, and Taxes The Fund has the potential to make the following distributions:

Types of Distributions

Dividends	Represents interest and dividends earned from securities held by the Fund, net of expenses incurred by the Fund.
Capital gains	Represents net long-term capital gains on sales of securities held for more than one year and net short-term capital gains on sales of securities held for a one-year period or less.

UNDERSTANDING FUND DISTRIBUTIONS

The Fund may earn income from the securities it holds. The Fund also may realize capital gains or losses on sales of its securities. The Fund intends to distribute substantially all of its net investment income and capital gains to shareholders each year. As a shareholder, you are entitled to a portion of the Fund's income and capital gains based on the number of shares you own at the time these distributions are declared.

Distribution Options The Fund distributes any dividends in June and December and any capital gains (including short-term capital gains) at least annually. You can choose one of the options listed in the table below for these distributions when you open your account. To change your distribution option call 1-800-345-6611.

If you do not indicate on your application or at the time your account is established your preference for handling distributions, the Fund will automatically reinvest all distributions in additional shares of the Fund.

Distribution Options

Reinvest all distributions in additional shares of the Fund

Reinvest all distributions in shares of another fund

Receive dividends in cash (see options below) and reinvest capital gains

Receive all distributions in cash (with one of the following options):

•  send the check to your address of record

•  send the check to a third-party address

•  transfer the money to your bank via electronic funds transfer

Distributions of $10 or less will automatically be reinvested in additional Fund shares. If you elect to receive distributions by check and the check is returned as undeliverable, all subsequent distributions will be reinvested in additional shares of the Fund.

Taxes Unless you are an entity exempt from income tax or invest under a retirement account, regardless of whether you receive your distributions in cash or reinvest them in additional Fund shares, all Fund distributions are subject to federal income tax. Depending on where you live, distributions also may be subject to state and local income taxes.

The Fund intends to elect to be treated and to qualify each year as a regulated investment company. A regulated investment company is not subject to tax at the corporate level on income and gains from investments that are distributed to shareholders in accordance with applicable law. However, the Fund's failure to qualify as a regulated investment company could result in corporate level taxation, and consequently, a reduction in income available for distribution to shareholders.

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Your Account

In general, any distributions of dividends, interest and short-term capital gains (determined by how long the Fund held the investments that generated them) are taxable as ordinary income, unless such dividends are "qualified dividend income" (as defined in the Internal Revenue Code) eligible for a reduced rate of tax. Properly designated distributions of long-term capital gains (determined by how long the Fund held the investments that generated them) are generally taxable as such, regardless of how long you have held your Fund shares. You will be provided with information each year regarding the amount of ordinary income and capital gains distributed to you for the previous year and any portion of your distribution which is exempt from state and local taxes. Long-term capital gain rates have been reduced — in general, to 15% with lower rates applying to taxpayers in the 10% and 15% rate brackets — for taxable years b eginning before January 1, 2011. Distributions are taxable to you even if they are paid from income or gains earned by the Fund before you made your investment (and thus were included in the price you paid).

Income other than net capital gains received by the Fund from the Portfolio Funds (including dividends and distributions of short-term capital gains) will be distributed by the Fund (after deductions for expenses) and will be taxable to you as ordinary income, unless it is eligible to be treated as qualified dividend income. Because the Fund is an asset allocation fund and may realize taxable net short-term capital gains by selling shares of a Portfolio Fund in its portfolio with unrealized portfolio appreciation, investing in the Fund rather than directly in the Portfolio Fund may result in accelerated tax liability to you since the Fund must distribute its gains in accordance with the Internal Revenue Code.

Distributions of net capital gains received by the Fund from its Portfolio Funds, plus net long-term capital gains realized by the Fund from the purchase and sale of Portfolio Fund shares or other securities held by the Fund for more than one year, will be distributed by the Fund and will be taxable to you as long-term capital gains (even if you have held Fund shares for one year or less). If a shareholder who has received a capital gains distribution suffers a loss on the sale of his or her shares not more than six months after purchase, the loss will be treated as a long-term capital loss to the extent of the capital gains distribution received. Long-term capital gains, including distributions of net capital gains, are currently subject to a maximum federal tax rate of 15%. This rate is less than the maximum rate imposed on other types of taxable income. Capital gains also may be advantageous since, unlike ordinary income, the y may be offset by capital losses.

For purposes of determining the character of income received by the Fund when a Portfolio Fund distributes net capital gains to the Fund, the Fund will treat the distribution as long-term capital gain, even if the Fund has held shares of the Portfolio Fund for one year or less. Any loss incurred by the Fund on the sale of that Portfolio Fund's shares held for six months or less, however, will be treated as a long-term capital loss to the extent of the net capital gain distribution.

High portfolio turnover may cause the Fund to realize short-term capital gains which, if realized and distributed by the Fund, may be taxable to shareholders as ordinary income. Distributions of long-term capital gains are generally taxable as such, regardless of how long you have held your Fund shares. You will be provided with information each year regarding the amount of ordinary income and capital gains distributed to you for the previous year and any portion of your distribution which is exempt from state and local taxes. Your investment in the Fund may have additional personal tax implications. Please consult your tax advisor about foreign, federal, state, local or other applicable tax laws.

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Your Account

In addition to the dividends and capital gains distributions made by the Fund, you may realize a capital gain or loss when selling or exchanging shares of the Fund. Such transactions also may be subject to federal, state and local income tax.

Board of Trustees

The Fund is governed by its Board of Trustees. More than 75% of the Fund's Trustees are independent, meaning that they have no affiliation with the adviser or the Funds, apart from their positions as Trustees and the personal investments they may have made as private individuals.

The independent Trustees bring backgrounds in business and the professions and academia to their task of working with the Funds' officers to establish the policies and oversee the activities of the Funds. Among the Trustees' responsibilities are selecting the investment adviser for the Funds; negotiating the advisory agreements; reviewing other contracts; approving investment policies; monitoring Fund operations, performance, and costs; and nominating or selecting new Trustees.

Each Trustee serves until his or her retirement, resignation, death or removal; or otherwise as specified in the Trust's organizational documents. It is expected that every five years the Trustees will call a meeting of shareholders to elect Trustees. A Trustee must retire at the end of the year in which he or she attains the age of 75. Any Trustee may be removed at a shareholders' meeting by a vote representing two-thirds of the net asset value of all shares of the Funds of the Trust. The mailing address for the Trustees and officers is 227 W. Monroe, Suite 3000, Chicago, Illinois 60606.

For more detailed information on the Board of Trustees, please refer to the SAI.

Managing the Fund

INVESTMENT ADVISER

Columbia Wanger Asset Management, L.P. (CWAM), located at 227 West Monroe Street, Suite 3000, Chicago, Illinois 60606, is the Fund's investment adviser and is responsible for the Fund's management, subject to oversight by the Fund's Board of Trustees. CWAM and its predecessor have managed mutual funds, including the Fund, since 1992. In its duties as investment adviser, CWAM runs the Fund's day-to-day business, including placing all orders for the purchase and sale of the Fund's portfolio securities.

CWAM was previously named Liberty Wanger Asset Management, L.P., and its predecessor was named Wanger Asset Management, L.P. (WAM). CWAM is a wholly owned subsidiary of Columbia Management Group, LLC, which in turn is an indirect wholly owned subsidiary of Bank of America Corporation. As of December 31, 2006, CWAM managed more than $32.9 billion in assets.

33

Managing the Fund

CWAM's advisory fee for managing the Fund in 2006 was 0.10% of the Fund's average daily net assets. CWAM also received an administrative fee from the Fund in 2006 of 0.04% of the Fund's average daily net assets. A discussion of the factors considered by the Fund's Board of Trustees in approving the Fund's investment advisory contract is included in the Fund's annual report to shareholders for the period ended December 31, 2006.

The Portfolio Funds are managed by CWAM and its affiliate Columbia Management Advisors, LLC, previously named Columbia Management Company (CMA). On April 1, 2003, Colonial Management Associates and Stein Roe & Farnham Incorporated and other affiliated investment adviser entities were merged with and into CMA. CMA assumed all of the business associated with each of the merged investment advisers. Like CWAM, CMA is owned by Columbia Management Group, LLC. CMA also may provide administrative and operational services to Thermostat.

PORTFOLIO MANAGER

The portfolio manager reviews on an infrequent basis the structure and allocation ranges of Thermostat and makes any changes considered appropriate.

Charles P. McQuaidLead portfolio manager

Charles McQuaid is president of the Trust and a member of the Trust's Board of Trustees. He has been president of CWAM since October 2003, chief investment officer of CWAM since October 2003, and was director of research at CWAM and its predecessor from July 1992 through December 2003. Mr. McQuaid has been a member of Columbia Acorn Fund's management team since 1978, co-managed Columbia Acorn Fund from 1995 through September 2003 and has been the Fund's lead portfolio manager since September 2003. He served as CWAM's interim director of international research from October 2003 to December 2004. Mr. McQuaid has been the president of Wanger Advisors Trust since 2003 and a trustee since September 2006. He also manages two domestic separate accounts and two offshore funds.

The SAI provides additional information about the portfolio manager's compensation, other accounts managed and ownership of securities in the Fund.

LEGAL PROCEEDINGS

The Trust, CWAM and the trustees of the Trust (collectively, the "Columbia defendants") are named as defendants in class and derivative complaints, which were consolidated in a Multi-District Action in the federal district court for the District of Maryland on February 20, 2004 (the "MDL Action"). These lawsuits contend that defendants permitted certain investors to market time their trades in certain Columbia Acorn Funds. The MDL Action is ongoing. All claims against the Trust and its independent trustees have been dismissed; however, the interested trustees of the Trust are still parties to the MDL Action.

On March 21, 2005, a class action complaint was filed against the Trust in the Superior Court of the Commonwealth of Massachusetts seeking to rescind the contingent deferred sales charges assessed upon redemption of Class B shares of Columbia Acorn Funds due to the alleged market timing by certain shareholders of the Columbia Acorn Funds. In addition to the rescission of sales charges, plaintiffs seek recovery of actual damages, attorneys' fees and costs. The case has been transferred to the MDL Action in the federal district court of Maryland.

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Managing the Fund

The Trust and CWAM are also defendants in a class action lawsuit, filed on November 13, 2003 in the Circuit Court of the Third Judicial Circuit, Madison County, Illinois, that alleges, in summary, that the Trust and CWAM exposed shareholders of Columbia Acorn International to trading by market timers by allegedly (a) failing to properly evaluate daily whether a significant event affecting the value of that fund's securities had occurred after foreign markets had closed but before the calculation of the fund's net asset value; (b) failing to implement the fund's portfolio valuation and share pricing policies and procedures; and (c) failing to know and implement applicable rules and regulations concerning the calculation of net asset value ( "Fair Valuation Lawsuit"). On April 5, 2005, the United States Court of Appeals for the Seventh Circuit ruled that the plaintiffs' state law claims were preempted under federal law resulting i n the dismissal of plaintiffs' complaint. Plaintiffs appealed the Seventh Circuit's ruling to the United States Supreme Court. On June 15, 2006, the Supreme Court reversed the Seventh Circuit's ruling on jurisdictional grounds, and the case ultimately was remanded to the state court.

On April 4, 2006, the plaintiffs and the Columbia defendants named in the MDL Action executed an agreement in principle intended to fully resolve all of the lawsuits consolidated in the MDL Action as well as the Fair Valuation Lawsuit. The court entered a stay after the parties executed the agreement in principle. The settlement is subject to court approval.

In 2004, CWAM and the trustees of the Columbia Acorn Trust were named as defendants in certain purported shareholder class and derivative actions making claims, including claims under the Investment Company and the Investment Advisers Acts of 1940 and state law. Certain Columbia Acorn Funds were named as nominal defendants. The suits allege, inter alia, that the fees and expenses paid by the funds are excessive and that the funds' advisers and their affiliates inappropriately used fund assets to distribute the funds and for other improper purposes. On March 2, 2005, the actions were consolidated in the Massachusetts federal court as In re Columbia Entities Litigation. The plaintiffs filed a consolidated amended complaint on June 9, 2005. On November 30, 2005, the judge dismissed all claims by plaintiffs and entered final judgment in favor of the defendants. The plaintiffs appealed to the United States Court of Appeals for the First Circuit on December 30, 2005. A stipulation and settlement agreement dated January 19, 2007 was filed in the First Circuit on February 14, 2007, with a joint stipulation of dismissal and motion for remand to obtain district court approval of the settlement. The joint motion was granted and the appeal was dismissed. On March 6, 2007, the case was remanded to the District Court, where the parties will seek court approval of the settlement. The terms of the proposed settlement, if approved, will require payments by the funds' adviser and/or its affiliates, including payment of plaintiffs' attorneys' fees and notice to class members. In the event that the settlement is not approved, the plaintiffs may elect to g o forward with their appeal and no opinion is expressed regarding the likely outcome or financial impact of such an appeal on any fund.

On or about January 11, 2005, a putative class action lawsuit was filed in federal district court in Massachusetts against Columbia Acorn Trust and its trustees, along with Columbia Management Advisors, LL, the sub-administrator of the Wanger Advisors Funds and the Columbia Acorn Funds. The plaintiffs allege that the defendants failed to submit Proof of Claims in connection with settlements of securities class action lawsuits filed against companies in which the Columbia Acorn Funds held positions. The complaint seeks compensatory and punitive damages, and the disgorgement of all fees paid to Columbia Management Advisors, LLC. Plaintiffs have voluntarily dismissed Columbia Acorn Trust and its independent trustees.

On or about January 11, 2005, a putative class action lawsuit was filed in federal district court in Massachusetts against the Trust and its trustees, along with Columbia Management Advisors, LLC, the sub-administrator of the Wanger Advisors Funds and the Columbia Acorn Funds. The plaintiffs allege that the defendants failed to submit

35

Managing the Fund

Proof of Claims in connection with settlements of securities class action lawsuits filed against companies in which the Columbia Acorn Funds held positions. The complaint seeks compensatory and punitive damages, and the disgorgement of all fees paid to Columbia Management Advisors, LLC. Plaintiffs have voluntarily dismissed the Trust and its independent trustees.

The Trust and CWAM intend to defend these suits vigorously.

As a result of these matters or any adverse publicity or other developments resulting from them, there may be increased redemptions or reduced sales of Fund shares, which could increase transaction costs or operating expenses, or have other adverse consequences for the Fund.

However, based on currently available information, the Trust believes that the likelihood that these lawsuits will have a material adverse impact on any fund is remote, and CWAM believes that the lawsuits are not likely to materially affect its ability to provide investment management services to the Fund.

Other Investment Strategies and Risks

Thermostat's principal investment strategies and associated risks are described under "The Fund — Principal Investment Strategies" and "The Fund — Principal Investment Risks." This section describes other investments the Portfolio Funds may make and the risks associated with them. In seeking to achieve their investment goals, the Portfolio Funds may invest in various types of securities and engage in various investment techniques that are not their principal focus and therefore are not described in this prospectus. These types of securities and investment practices and their associated risks are identified and discussed in Thermostat's SAI, which you may obtain free of charge (see back cover). The adviser may elect not to buy any of these securities or use any of these techniques. The Fund may not always achieve its investment goal. Except as otherwise noted, approval by Thermostat's shareholders is not required to mod ify or change Thermostat's investment strategies.

DERIVATIVE STRATEGIES

The Portfolio Funds may enter into a number of hedging strategies, including those that employ futures, options, straddles or similar investments, to gain or reduce exposure to particular securities or markets. These strategies, commonly referred to as derivatives, involve the use of financial instruments whose values depend on, or are derived from, the value of an underlying security, index or currency. The Portfolio Funds may use these strategies to adjust for both hedging and non-hedging purposes, such as to adjust their sensitivity to changes in interest rates, or to offset a potential loss in one position by establishing an interest in an opposite position. Derivative strategies involve the risk that they may exaggerate a loss, potentially losing more money than the actual cost of the underlying security, or limit a potential gain. Also, with some derivative strategies there is a risk that the other party to the transaction may fail to honor its contract terms, causing a loss to a Portfolio Fund or that the Portfolio Fund may not be able to find a suitable derivative transaction counterparty, and thus may be unable to invest in derivatives altogether.

36

Other Investment Strategies and Risks

WHEN-ISSUED SECURITIES AND FORWARD COMMITMENTS

When-issued securities and forward commitments are securities that are purchased prior to the date they are actually issued or delivered. These securities involve the risk that they may fall in value by the time they are actually issued or that the other party may fail to honor the contract terms.

SHORT SALES

A Portfolio Fund's short sales are subject to special risks. A short sale involves the sale by a Portfolio Fund of a security that it borrows from a third party in the hope of purchasing the same security at a later date at a lower price. In order to deliver the security to the buyer, a Portfolio Fund borrows the security from a third party. The Portfolio Fund is then obligated to return the security to the third party, requiring the Portfolio Fund to purchase the security at the market price at some later date. If the price of the security has increased, then the Portfolio Fund will incur a loss equal to the increase in price of the security from the time that the short sale was entered into, plus any premiums and interest paid to the third party. Therefore, short sales involve the risk that losses may be exaggerated, potentially losing more money than the actual cost of the security at the time it is sold short. Also, there is the risk that the third party to the short sale may fail to honor its contract terms, causing a loss to the Portfolio Fund.

ASSET-BACKED SECURITIES

Asset-backed securities are interests in pools of debt securities backed by various types of loans such as credit card, auto and home equity loans. These securities involve prepayment risk, which is the possibility that the underlying debt may be refinanced or prepaid prior to maturity during periods of declining interest rates. A decline in interest rates may lead to a faster rate of repayment on asset-backed securities and therefore, cause a Portfolio Fund to earn a lower interest rate on reinvestment. In addition, the potential impact of prepayment on the price of an asset-backed security may be difficult to predict and result in greater volatility. During periods of rising interest rates, asset-backed securities have a high risk of declining in price because the declining prepayment rates effectively increase the maturity of the securities.

MORTGAGE-BACKED SECURITIES

Mortgage-backed securities are securities that represent ownership interests in large, diversified pools of mortgage loans. Sponsors pool together mortgages of similar rates and terms and offer them as a security to investors.

Most mortgage securities are pooled together and structured as pass-throughs. Monthly payments of principal and interest from the underlying mortgage loans backing the pool are collected by a servicer and "passed through" regularly to the investor. Pass-throughs can have a fixed or an adjustable rate. The majority of pass-through securities are issued by three agencies: Ginnie Mae, Fannie Mae, and Freddie Mac. These securities involve prepayment risk, which is the possibility that the underlying debt may be refinanced or prepaid prior to maturity during periods of declining interest rates. A decline in interest rates may lead to a faster rate of repayment on mortgage-backed securities and, therefore, cause the Fund to earn a lower interest rate on reinvestment. In addition, the potential impact of prepayment on the price of a mortgage-backed security may be difficult to predict and result in greater volatility. During periods of rising interest rates, mortgage-backed securities have a

37

Other Investment Strategies and Risks

high risk of declining in price because the declining prepayment rates effectively increase the maturity of the securities.

Commercial mortgaged-backed securities are secured by loans to commercial properties such as office buildings, multi-family apartment buildings, and shopping centers. These loans usually contain prepayment penalties that provide protection from refinancing in a declining interest rate environment.

Real estate mortgage investment conduits (REMICs) are multi-class securities that qualify for special tax treatment under the Internal Revenue Code. REMICs invest in certain mortgages that are secured principally by interests in real property such as single family homes.

ZERO COUPON BONDS

Zero coupon bonds do not pay interest in cash on a current basis, but instead accrue interest over the life of the bond. As a result, these securities are issued at a discount. The value of these securities may fluctuate more than the value of similar securities that pay interest periodically. Although these securities pay no interest to holders prior to maturity, interest accrued on these securities is reported as income to a Portfolio Fund and distributed to its shareholders.

ILLIQUID INVESTMENTS

A Portfolio Fund may invest up to 15% of its net assets in illiquid investments. An illiquid investment is a security or other position that cannot be disposed of quickly in the normal course of business. For example, some securities are not registered under U.S. securities laws and cannot be sold in public transactions because of Securities and Exchange Commission regulations (these are known as "restricted securities"). Under procedures adopted by a Portfolio Fund's board of trustees, certain restricted securities may be deemed liquid and will not be counted toward this 15% limit.

TEMPORARY DEFENSIVE STRATEGIES

At times, CWAM or the advisers to the Portfolio Funds may determine that adverse market conditions make it desirable to temporarily suspend the Fund's or Portfolio Funds' respective normal investment activities. During such times, the Fund or Portfolio funds may, but are not required to, invest in cash or high-quality, short-term debt securities, without limit. Taking a temporary defensive position may prevent the Fund or Portfolio Funds from achieving their respective investment goals.

38

Financial Highlights

The financial highlights table is intended to help you understand the Fund's financial performance. Information is shown for the Fund's fiscal years since inception, which run from January 1 to December 31, unless otherwise indicated. Certain information in the table reflects the financial results for a single Class A, B or C share. The total returns in the table represent the return that you would have earned (or lost) on an investment in the Fund (assuming reinvestment of all dividends and distributions). This information has been derived from the Fund's financial statements, which have been audited for the years ended December 31, 2004, 2005 and 2006 by PricewaterhouseCoopers LLP, an independent registered public accounting firm, whose report, along with the Fund's financial statements, is included in the Fund's annual report. The information for the period ended December 31, 2003 is included in the Fund's financial statement s that have been audited by another independent registered public accounting firm, whose report expressed an unqualified opinion on those financial statements and highlights. You can request a free annual report containing those financial statements by calling 1-800-345-6611.

Columbia Thermostat Fund

	Year Ended December 31,									Inception March 3, 2003 through
	2006			2005			2004			December 31, 2003
	Class A			Class A			Class A			Class A
Net asset value — Beginning of period ($)		12.49			13.11			12.30			10.10
Income from Investment Operations ($):
Net investment income(a)		.45			0.39			0.28			0.18
Net realized and unrealized gain		.84			0.29			0.81			2.15
Total from Investment Operations		1.29			0.68			1.09			2.33
Less Distributions Declared to Shareholders ($):
From net investment income		(0.47	)		(0.39	)		(0.25	)		(0.13	)
From net realized gains		(0.72	)		(0.91	)		(0.03	)		(0.00	)(b)
Total Distributions Declared to Shareholders		(1.19	)		(1.30	)		(0.28	)		(0.13	)
Net asset value — End of period ($)		12.59			12.49			13.11			12.30
Total return (%)(c)(d)		10.56			5.25			8.92			23.10	(e)
Ratios to Average Net Assets/Supplemental Data (%):
Expenses(f)(g)		0.50			0.50			0.50			0.57	(h)
Net investment income(g)		3.53			2.97			2.23			1.86	(h)
Reimbursement/waiver		0.20			0.15			0.33			0.66	(h)
Portfolio turnover rate (%)		66			96			67			61
Net assets at end of period (000's) ($)		58,013			71,034			77,092			42,271

(a)  Per share data was calculated using average shares outstanding during the period. Recognition of net investment income by the Fund is affected by the timing of the declaration of dividends by the underlying investment companies in which the Fund invests.

(b)  Rounds to less than $(0.01) per share.

(c)  Total return at net asset value assuming all distributions reinvested and no initial sales charge or contingent deferred sales charge.

(d)  Had the investment adviser and/or transfer agent not reimbursed a portion of expenses, total return would have been reduced.

(e)  Not annualized.

(f)  Does not include expenses of the investment companies in which the Fund invests.

(g)  The benefits derived from custody fees paid indirectly had no impact.

(h)  Annualized.

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Financial Highlights

Columbia Thermostat Fund

	Year Ended December 31,									Inception March 3, 2003 through
	2006			2005			2004			December 31, 2003
	Class B			Class B			Class B			Class B
Net asset value — Beginning of period ($)		12.51			13.14			12.32			10.10
Income from Investment Operations ($):
Net investment income(a)		0.38			0.31			0.19			0.10
Net realized and unrealized gain		0.84			0.28			0.83			2.16
Total from Investment Operations		1.22			0.59			1.02			2.26
Less Distributions Declared to Shareholders ($):
From net investment income		(0.39	)		(0.31	)		(0.17	)		(0.04	)
From net realized gains		(0.72	)		(0.91	)		(0.03	)		(0.00	)(b)
Total Distributions Declared to Shareholders		(1.11	)		(1.22	)		(0.20	)		(0.04	)
Net asset value — End of period ($)		12.62			12.51			13.14			12.32
Total return (%)(c)(d)		9.91			4.56			8.27			22.38	(e)
Ratios to Average Net Assets/Supplemental Data (%):
Expenses(f)(g)		1.06			1.10			1.18			1.32	(h)
Net investment income(g)		2.99			2.39			1.55			1.06	(h)
Reimbursement/waiver		0.23			0.19			0.29			0.66	(h)
Portfolio turnover rate (%)		66			96			67			61
Net assets at end of period (000's) ($)		72,367			78,444			78,040			51,501

(a)  Per share data was calculated using average shares outstanding during the period. Recognition of net investment income by the Fund is affected by the timing of the declaration of dividends by the underlying investment companies in which the Fund invests.

(b)  Rounds to less than $(0.01) per share.

(c)  Total return at net asset value assuming all distributions reinvested and no initial sales charge or contingent deferred sales charge.

(d)  Had the investment adviser and/or transfer agent not reimbursed a portion of expenses, total return would have been reduced.

(e)  Not annualized.

(f)  Does not include expenses of the investment companies in which the Fund invests.

(g)  The benefits derived from custody fees paid indirectly had no impact.

(h)  Annualized.

40

Financial Highlights

Columbia Thermostat Fund

	Year Ended December 31,									Inception March 3, 2003 through
	2006			2005			2004			December 31, 2003
	Class C			Class C			Class C			Class C
Net asset value — Beginning of period ($)		12.51			13.13			12.32			10.10
Income from Investment Operations ($):
Net investment income(a)		0.36			0.29			0.19			0.11
Net realized and unrealized gain		0.84			0.29			0.81			2.15
Total from Investment Operations		1.20			0.58			1.00			2.26
Less Distributions Declared to Shareholders ($):
From net investment income		(0.37	)		(0.29	)		(0.16	)		(0.04	)
From net realized gains		(0.72	)		(0.91	)		(0.03	)		(0.00	)(b)
Total Distributions Declared to Shareholders		(1.09	)		(1.20	)		(0.19	)		(0.04	)
Net asset value — End of period ($)		12.62			12.51			13.13			12.32
Total return (%)(c)(d)		9.72			4.49			8.13			22.38	(e)
Ratios to Average Net Assets/Supplemental Data (%):
Expenses(f)(g)		1.25			1.25			1.25			1.32	(h)
Net investment income(g)		2.81			2.21			1.48			1.10	(h)
Reimbursement/waiver		0.23			0.19			0.26			0.66	(h)
Portfolio turnover rate (%)		66			96			67			61
Net assets at end of period (000's) ($)		27,375			28,316			31,161			20,087

(a)  Per share data was calculated using average shares outstanding during the period. Recognition of net investment income by the Fund is affected by the timing of the declaration of dividends by the underlying investment companies in which the Fund invests.

(b)  Rounds to less than $(0.01) per share.

(c)  Total return at net asset value assuming all distributions reinvested and no initial sales charge or contingent deferred sales charge.

(d)  Had the investment adviser and/or transfer agent not reimbursed a portion of expenses, total return would have been reduced.

(e)  Not annualized.

(f)  Does not include expenses of the investment companies in which the Fund invests.

(g)  The benefits derived from custody fees paid indirectly had no impact.

(h)  Annualized.

41

Appendix A

The following after tax returns of the Portfolio Funds are calculated using the historical highest individual federal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor's tax situation and may differ from those shown, and may not be relevant to investors who hold Portfolio Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

UNDERSTANDING PERFORMANCE

Average annual total returns are a measure of a Portfolio Fund's average performance over the past one-year, five-year and ten-year (or life of Fund) periods. They include the effects of Portfolio Fund expenses.

The Portfolio Fund's returns are compared to an index selected by the Portfolio Funds' adviser. All third-party trademarks are the property of their owners. Unlike each Portfolio Fund, indices are not investments, do not incur fees, expenses or taxes, and are not professionally managed. It is not possible to invest directly in an index.

Average Annual Total Returns — for periods ended December 31, 2006

	Inception Date	1 Year		5 Years		10 Years
Columbia Acorn Fund, Class Z(1) (%)	6/10/70
Return Before Taxes			14.45		14.71		15.16
Return After Taxes on Distributions			12.95		14.07		13.52
Return After Taxes on Distributions and Sale of Fund Shares			11.04		12.85		12.80
Russell 2500® Index (%)	n/a		16.17		12.19		11.26
S&P 500 Index (%)			15.79		6.19		8.42
Russell 2000® Index (%)			18.37		11.39		9.44

(1)  The Fund's Class Z share total net annual fund operating expenses at December 31, 2006 were 0.74%; Class Z and total net assets of the Fund were (in thousands) $12,127,573 and $18,945,126, respectively.

	Inception Date	1 Year		5 Years		Life of the Fund
Columbia Acorn Select, Class Z(1) (%)	11/23/98
Return Before Taxes			19.68		13.67		15.30
Return After Taxes on Distributions			19.11		13.36		14.76
Return After Taxes on Distributions and Sale of Fund Shares			13.21		11.93		13.46
S&P MidCap 400 Index (%)	n/a		10.32		10.89		11.94

(1)  The Fund's Class Z share total net annual fund operating expenses at December 31, 2006 were 0.96%; Class Z and total net assets of the Fund were (in thousands) $909,442 and $2,237,711, respectively.

(2)  Performance information is from November 23, 1998.

42

Appendix A

	Inception Date	1 Year		5 Years		Life of Fund
Columbia Marsico Growth Fund, Class Z(1) (%)	12/31/97
Return Before Taxes			7.18		7.58		8.42
Return After Taxes on Distributions			7.18		7.58		8.37
Return After Taxes on Distributions and Sale of Fund Shares			4.67		6.58		7.42
S&P 500 Index (%)	n/a		15.79		6.19		5.96	(2)

(1)  The Fund's Class Z share total net annual fund operating expenses at March 31, 2006 were 0.96%; Class Z and total net assets of the Fund were (in thousands) $1,446,667 and $4,281,982, respectively.

(2)  Performance information is from December 31, 1997.

	Inception Date	1 Year		5 Years		10 Years(2)
Columbia Acorn International Fund, Class Z(1) (%)	9/22/92
Return Before Taxes			34.53		21.35		13.15
Return After Taxes on Distributions			32.08		20.68		12.01
Return After Taxes on Distributions and Sale of Fund Shares			24.72		18.86		11.26
S&P/Citigroup EMI Global ex-U.S. Index (%)	n/a		30.83		24.39		10.65
MSCI EAFE Index			26.34		14.98		7.71
S&P/Citigroup Global ex-U.S. Cap Range $500M — $5B Index (%)			26.70		24.15		10.86

(1)  The Fund's Class Z share total net annual fund operating expenses at December 31, 2006 were 0.94%; Class Z and total net assets of the Fund were (in thousands) $3,836,404 and $4,343,395, respectively.

(2)  The Fund's performance in 1999 was achieved during a period of unusual market conditions.

	Inception Date	1 Year		5 Years		Life of Fund
Columbia Dividend Income Fund, Class Z(1) (%)	3/4/98
Return Before Taxes			20.07		7.34		7.97
Return After Taxes on Distributions			19.51		6.97		6.85
Return After Taxes on Distributions and Sale of Fund Shares			13.72		6.24		6.30
Russell 1000 Value Index (%)	n/a		22.25		10.86		8.09	(2)

(1)  The Fund's Class Z share total net annual fund operating expenses at September 30, 2006 were 0.80%; Class Z and total net assets of the Fund were (in thousands) $471,876 and $986,291, respectively.

(2)  Performance information is from March 4, 1998.

	Inception Date	1 Year		5 Years		10 years
Columbia Large Cap Enhanced Core Fund, Class Z(1) (%)	7/31/96
Return Before Taxes			16.81		6.97		8.46
Return After Taxes on Distributions			14.57		5.29		6.85
Return After Taxes on Distributions and Sale of Fund Shares			11.40		5.06		6.63
S&P 500 Index (%)	n/a		15.79		6.19		8.42	(2)

(1)  The Fund changed its fiscal year end from March 31 to February 28. The Fund's Class Z share total net annual fund operating expenses at March 31, 2006 were 0.50%; Class Z and total net assets of the Fund were (in thousands) $495,099 and $513,618, respectively.

(2)  Performance information is from July 31, 1996.

43

Appendix A

	Inception Date(1)	1 Year		5 Years		10 Years
Columbia Federal Securities Fund, Class Z(2) (%)	1/11/99
Return Before Taxes			3.74		4.40		5.56
Return After Taxes on Distributions			2.04		2.73		3.39
Return After Taxes on Distributions and Sale of Fund Shares			2.40		2.76		3.40
Lehman Brothers Intermediate U.S. Government Bond Index (%)	n/a		3.84		3.92		5.48

(1)  [Class Z is a newer class of shares. Its performance information includes returns of the Fund's Class A shares (the oldest existing fund class) for periods prior to its inception. These returns have not been restated to reflect any differences in expenses (such as Rule 12b-1 fees) between Class A shares and the newer class of shares. The Class A share returns have been adjusted to take into account the fact that Class Z shares are sold without sales charges. If differences in expenses had been reflected, the returns shown for periods prior to the inception of the newer class of shares would have been higher, since Class Z shares are not subject to service fees. Class A shares were initially offered on March 30, 1984, and Class Z shares were initially offered on January 11, 1999.]

(2)  The Fund's Class Z share total net annual fund operating expenses at August 31, 2006 were 0.72%; Class Z and total net assets of the Fund were (in thousands) $109,187 and $848,598, respectively.

	Inception Date	1 Year		5 Years		10 Years
Columbia Intermediate Bond Fund, Class Z(1) (%)	12/5/78
Return Before Taxes			4.60		5.41		6.37
Return After Taxes on Distributions			2.76		3.43		3.97
Return After Taxes on Distributions and Sale of Fund Shares			2.95		3.44		3.95
Lehman Brothers Aggregate Bond Index (%)	n/a		4.33		5.06		6.24

(1)  The Fund's Class Z share total net annual fund operating expenses at March 31, 2006 were 0.64%; Class Z and total net assets of the Fund were (in millions) $1,379 and $1,693, respectively.

	Inception Date	1 Year		5 Years		10 Years
Columbia Conservative High Yield Fund, Class Z(1) (%)	10/1/93
Return Before Taxes			6.17		5.73		6.09
Return After Taxes on Distributions			3.76		3.28		3.13
Return After Taxes on Distributions and Sale of Fund Shares			3.95		3.41		3.34
Merrill Lynch U.S. High Yield, Cash Pay Index (%)	n/a		11.64		9.85		6.86
JP Morgan Developed BB High Yield Index			8.67		8.98		8.14

(1)  The Fund's Class Z share total net annual fund operating expenses at August 31, 2006 were 0.72%; Class Z and total net assets of the Fund were (in millions) $802 and $1,087, respectively.

44

APPENDIX B

Hypothetical Investment and Expense Information

The Fund is required to disclose the following supplemental hypothetical investment information, which provides additional information about the effect of the expenses paid by the Fund, including investment advisory fees and other Fund costs, on the Fund's returns over a 10-year period. The tables show the estimated expenses that would be charged on a hypothetical investment of $10,000 in each class of the Fund assuming a 5% return each year, the cumulative return after fees and expenses, and the hypothetical year-end balance after fees and expenses. The tables also assume that all dividends and distributions are reinvested and that Class B shares convert to Class A shares after eight years. The annual expense ratios used for the Fund, which are the same as those stated in the Annual Fund Operating Expenses table, are presented in the tables, and are net of any contractual fee waivers or expense reimbursements for the period of the contractual commitment. Your actual costs may be higher or lower. The tables shown below reflect the maximum initial sales charge for Class A shares but do not reflect any contingent deferred sales charges which may be payable on redemption. If contingent deferred sales charges were reflected, the "Hypothetical Year-End Balance After Fees and Expenses" amounts shown would be lower and the "Annual Fees and Expenses" amounts shown would be higher.

Columbia Thermostat Fund — Class A Shares

Maximum Sales Charge 5.75%					Initial Hypothetical Investment Amount $10,000.00						Assumed Rate of Return 5%
Year		Cumulative Return Before Fees & Expenses			Annual Expense Ratio			Cumulative Return After Fees & Expenses			Hypothetical Year-End Balance After Fees & Expenses		Annual Fees & Expenses(1)
	1		5.00	%		1.19	%		-2.16	%(2)	$	9,784.09	$	689.30
	2		10.25	%		1.35	%		1.41	%	$	10,141.21	$	134.50
	3		15.76	%		1.35	%		5.11	%	$	10,511.36	$	139.41
	4		21.55	%		1.35	%		8.95	%	$	10,895.02	$	144.50
	5		27.63	%		1.35	%		12.93	%	$	11,292.69	$	149.77
	6		34.01	%		1.35	%		17.05	%	$	11,704.87	$	155.24
	7		40.71	%		1.35	%		21.32	%	$	12,132.10	$	160.90
	8		47.75	%		1.35	%		25.75	%	$	12,574.92	$	166.77
	9		55.13	%		1.35	%		30.34	%	$	13,033.90	$	172.86
	10		62.89	%		1.35	%		35.10	%	$	13,509.63	$	179.17
Total Gain After Fees & Expenses											$	3,509.63
Total Annual Fees & Expenses													$	2,092.42

(1)  Annual Fees and Expenses are calculated based on the average between the beginning and ending balance for each year. All information is calculated on an annual compounding basis.

(2)  Reflects deduction of the maximum initial sales charge.

45

Appendix B

Columbia Thermostat Fund — Class B Shares

Maximum Sales Charge 0.00%					Initial Hypothetical Investment Amount $10,000.00						Assumed Rate of Return 5%
Year		Cumulative Return Before Fees & Expenses			Annual Expense Ratio			Cumulative Return After Fees & Expenses			Hypothetical Year-End Balance After Fees & Expenses		Annual Fees & Expenses(1)
	1		5.00	%		1.69	%		3.31	%	$	10,331.00	$	171.80
	2		10.25	%		1.88	%		6.53	%	$	10,653.32	$	197.25
	3		15.76	%		1.88	%		9.86	%	$	10,985.71	$	203.41
	4		21.55	%		1.88	%		13.28	%	$	11,328.46	$	209.76
	5		27.63	%		1.88	%		16.82	%	$	11,681.90	$	216.30
	6		34.01	%		1.88	%		20.46	%	$	12,046.38	$	223.05
	7		40.71	%		1.88	%		24.22	%	$	12,422.22	$	230.01
	8		47.75	%		1.88	%		28.10	%	$	12,809.79	$	237.18
	9		55.13	%		1.35	%		32.77	%	$	13,277.35	$	176.09
	10		62.89	%		1.35	%		37.62	%	$	13,761.97	$	182.52
Total Gain After Fees & Expenses											$	3,761.97
Total Annual Fees & Expenses													$	2,047.37

(1)  Annual Fees and Expenses are calculated based on the average between the beginning and ending balance for each year. All information is calculated on an annual compounding basis.

46

Appendix B

Columbia Thermostat Fund — Class C Shares

Maximum Sales Charge 0.00%					Initial Hypothetical Investment Amount $10,000.00						Assumed Rate of Return 5%
Year		Cumulative Return Before Fees & Expenses			Annual Expense Ratio			Cumulative Return After Fees & Expenses			Hypothetical Year-End Balance After Fees & Expenses		Annual Fees & Expenses(1)
	1		5.00	%		1.94	%		3.06	%	$	10,306.00	$	196.97
	2		10.25	%		2.15	%		6.00	%	$	10,599.72	$	224.74
	3		15.76	%		2.15	%		9.02	%	$	10,901.81	$	231.14
	4		21.55	%		2.15	%		12.13	%	$	11,212.51	$	237.73
	5		27.63	%		2.15	%		15.32	%	$	11,532.06	$	244.51
	6		34.01	%		2.15	%		18.61	%	$	11,860.72	$	251.47
	7		40.71	%		2.15	%		21.99	%	$	12,198.75	$	258.64
	8		47.75	%		2.15	%		25.46	%	$	12,546.41	$	266.01
	9		55.13	%		2.15	%		29.04	%	$	12,903.98	$	273.59
	10		62.89	%		2.15	%		32.72	%	$	13,271.75	$	281.39
Total Gain After Fees & Expenses											$	3,271.75
Total Annual Fees & Expenses													$	2,466.19

(1)  Annual Fees and Expenses are calculated based on the average between the beginning and ending balance for each year. All information is calculated on an annual compounding basis.

47

Notes

48

Notes

49

Notes

50

FOR MORE INFORMATION

Additional information about the Fund's investments will be published in the Fund's semiannual and annual reports to shareholders. The annual report will contain a discussion of the market conditions and investment strategies that significantly affected the Fund's performance during its last fiscal year.

You may wish to read the SAI for more information on the Fund and the securities in which it invests. The SAI is incorporated into this prospectus by reference, which means that it is considered to be part of this prospectus.

You can get free copies of annual and semiannual reports and the SAI, request other information and discuss your questions about the Fund by visiting www.columbiafunds.com or by writing or calling the Fund's transfer agent at:

Columbia Management Services, Inc.
P.O. Box 8081
Boston, MA 02266-8081
1-800-345-6611

Text-only versions of all Fund documents can be viewed online or downloaded from the EDGAR database on the Securities and Exchange Commission internet site at www.sec.gov.

You can review and copy information about the Fund, including the SAI, by visiting the following location, and you can obtain copies upon payment of a duplicating fee, by electronic request at the e-mail address publicinfo@sec.gov or by writing the:

Public Reference Room
Securities and Exchange Commission
Washington, DC 20549-0102

Information on the operation of the Public Reference Room may be obtained by calling 1-202-942-8090.

Investment Company Act file number:
Columbia Acorn Trust: 811-01829
•  Columbia Thermostat Fund

©2007 Columbia Management Distributors, Inc.
One Financial Center, Boston, MA 02111-2621
800.426.3750 www.columbiafunds.com

INT-36/130115-0507

Columbia^SM

Thermostat Fund^SM  Prospectus, May 1, 2007

Class Z Shares

Advised by Columbia Wanger Asset Management, L.P.

TABLE OF CONTENTS

THE FUND	2
Investment Goal	2
Principal Investment Strategies	2
Principal Investment Risks	10
Portfolio Holdings Disclosure	14
Performance History	14
Your Expenses	16
YOUR ACCOUNT	18
How to Buy Shares	18
Eligible Investors	19
Sales Charges ("Commissions")	21
How to Exchange Shares	21
How to Sell Shares	22
Fund Policy on Trading of Fund Shares	23
Financial Intermediary Payments	24
Other Information About Your Account	25
BOARD OF TRUSTEES	28
MANAGING THE FUND	29
Investment Adviser	29
Portfolio Manager	29
Legal Proceedings	30
OTHER INVESTMENT STRATEGIES AND RISKS	32
Derivative Strategies	32
When-Issued Securities and Forward Commitments	32
Short Sales	32
Asset-Backed Securities	33
Mortgage-Backed Securities	33
Zero Coupon Bonds	33
Illiquid Investments	34
Temporary Defensive Strategies	34
FINANCIAL HIGHLIGHTS	35
APPENDIX A	36
APPENDIX B	39

Only eligible investors may purchase Class Z shares. See "Your Account — Eligible Investors" for more information.

Although these securities have been registered with the Securities and Exchange Commission, the Commission has not approved or disapproved any shares offered in this prospectus or determined whether this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Acorn Thermostat is a trademark owned and registered by Columbia Acorn Trust, Columbia, Columbia Management^® and Columbia Management Services, Inc. are service marks owned and/or registered by Bank of America

The Fund

INVESTMENT GOAL

Columbia Thermostat Fund (Thermostat Fund^SM or Thermostat) seeks to provide long-term total return.

PRINCIPAL INVESTMENT STRATEGIES

Thermostat Fund pursues its investment goal by investing in other mutual funds. As a "fund of funds," under normal circumstances, Thermostat allocates at least 95% of its net assets (stock/bond assets) among a selected group of stock and bond mutual funds (Portfolio Funds) according to the current level of the Standard & Poor's 500 Stock Index (S&P 500) in relation to predetermined ranges set by the Fund's investment adviser. When the S&P 500 goes up, the Fund sells a portion of its stock funds and invests more in the bond funds; and when the S&P 500 goes down, the Fund increases its investment in the stock funds. Under normal circumstances, Thermostat may invest up to 5% of its net assets plus any cash received that day in cash, high quality short-term paper and government securities.

Asset allocation funds generally move assets from stocks to bonds when the market goes up, and from bonds to stocks when the market goes down. Most asset allocation funds are run by sophisticated investment professionals, who make subjective decisions based on economic and financial data and complex graphs of market behavior. By contrast, the day-to-day investment decisions for Thermostat are made according to a single predetermined rule. The temperature in your house is run by a single rule; your thermostat turns on the furnace if your house is too cold or turns on the air conditioner if your house is too warm. This Fund works the same way, so it is named Thermostat Fund.

Because Thermostat invests according to a pre-set program, there is no need for subjective day-to-day management. Although another successful asset allocation strategy might do better than Thermostat, Thermostat is designed for those who doubt the wisdom of trying to "time" the market and are unsure of the long-term trend of the stock market. Thermostat takes psychology out of investing; it avoids the temptation to buy more stocks because the stock market is currently going up or to sell stocks because the market is declining. Thermostat operates continuously and substantially automatically, subject to periodic review of the pre-set program by Thermostat Fund's adviser and its Board of Trustees. As described on page 5, the the portfolio manager has authority to review the structure and allocation ranges of the stock-bond allocation table and to make any changes considered appropriate.

The Portfolio Funds are chosen by Thermostat's adviser to provide participation in the major sectors of the stock and bond markets. If you believe that the stock market will tend to go up most of the time, then you should probably own a fully-invested stock fund and use a buy-and-hold strategy. Buy-and-hold was an excellent strategy in the 1982-1999 bull market. However, there have been long periods in the past when buy-and-hold was not the best strategy, such as 1930-1954 and 1969-1981, when the market fluctuated but did not make significant new highs. Thermostat may be a good investment choice for you if you believe that the market may fluctuate in a trading range for many years.

2

The Fund

Thermostat invests the stock/bond assets among the Portfolio Funds according to an asset allocation table. The current allocation table is set forth below:

Stock/Bond Allocation Table

	How Thermostat will Invest the Stock/Bond Assets
Level of the S&P 500	Stock Percentage			Bond Percentage
over 1800		0	%		100	%
over 1750-1800		5			95
over 1700-1750		10			90
over 1650-1700		15			85
over 1600-1650		20			80
over 1550-1600		25			75
over 1500-1550		30			70
over 1450-1500		35			65
over 1400-1450		40			60
over 1350-1400		45			55
over 1300-1350		50			50
over 1250-1300		55			45
over 1200-1250		60			40
over 1150-1200		65			35
over 1100-1150		70			30
over 1050-1100		75			25
over 1000-1050		80			20
over 950-1000		85			15
over 900-950		90			10
over 850-900		95			5
850 and under		100			0

When the S&P 500 moves into a new band on the table, the Fund promptly will rebalance the stock-bond mix to reflect the new S&P price level by redeeming shares of some Portfolio Funds and exchanging shares of other Portfolio Funds. The only exception will be a "31-day Rule"; in order to reduce taxable events, after the Fund has increased its percentage allocation to either stock funds or bond funds, it will not decrease that allocation for at least 31 days. Following a change in the Fund's stock-bond index, if the S&P 500 remains within the same band for a while, normal market fluctuations will change the values of the Fund's holdings of stock Portfolio Funds and bond Portfolio Funds. We will invest cash flows from sales (or redemptions) of Fund shares to bring the stock-bond mix back toward the allocation percentages for that S&P 500 band. For example, if the S&P 500 is in the 1000-1050 band, and the value o f the holdings of the stock Portfolio Funds has dropped to 68% of the value of the holdings of all Portfolio Funds, new cash would be invested in the stock Portfolio Funds (or cash for redemptions would come from the bond Portfolio Funds.) If the 31-day Rule is in effect, new cash flows will be invested at the stock-bond percentage allocation as of the latest rebalancing.

3

The Fund

As an illustrative example, suppose the following market events occurred:

Date	Level of the S&P 500	How Thermostat will invest the Stock/Bond Assets
Nov. 1	We begin when the market is 1340	50% stocks, 50% bonds
Dec. 1	The S&P 500 goes to 1351	rebalance 45% stocks, 55% bonds
Dec. 6	The S&P 500 drops back to 1345	no reversal for 31 days
Jan. 2	The S&P 500 is at 1342	rebalance 50% stocks, 50% bonds
Jan. 20	The S&P 500 drops to 1299	rebalance 55% stocks, 45% bonds
	The market has made a continuation move by going through a second action level, not a reversal move, so the 31-day Rule does not apply in this case.
Jan. 30	The S&P 500 goes up to 1305	no reversal for 31 days
Feb. 20	The S&P 500 is at 1310 rebalance	50% stocks, 50% bonds

The following table shows the six stock Portfolio Funds and three bond Portfolio Funds that Thermostat currently uses in its fund-of-funds structure and the current allocation percentage for each Portfolio Fund within the stock or bond category. The allocation percentage within each category is achieved by rebalancing the investments within the category whenever the S&P 500 moves into a new band on the allocation table, subject to the 31-day Rule described above. Thermostat does not liquidate its investment in one Portfolio Fund in order to invest in another Portfolio Fund except in connection with a rebalancing due to a move of the S&P 500 into a new band (or due to a change by the portfolio manager in the stock-bond allocation table in the Portfolio Funds or in the relative allocation among Portfolio Funds). Until a subsequent rebalancing, Thermostat's investments in, and redemptions from, the stock Portfolio Funds or the bond Portfolio Funds are allocated among such Portfolio Funds in a manner that will reduce any deviation of the relative values of Thermostat's holdings of such funds from the allocation percentages shown below.

Allocation of Stock/Bond Assets within Asset Classes

Stock Funds	Type of Fund	Allocation
Columbia Acorn Fund	Small-/Mid-cap growth		15	%
Columbia Acorn Select	Mid-cap growth		10	%
Columbia Marisco Growth Fund	Large-cap growth		15	%
Columbia Acorn International	Small/mid-cap international growth		15	%
Columbia Dividend Income Fund	Large-cap value		20	%
Columbia Large Cap Enhanced Core Fund(1)	Large-cap blend		25	%
Total			100	%
Bond Funds	Type of Fund	Allocation
Columbia Federal Securities Fund	U.S. government securities		30	%
Columbia Intermediate Bond Fund	Intermediate-term bonds		50	%
Columbia Conservative High Yield Fund	High-yield bonds		20	%
Total			100	%

(1)  Nations LargeCap Enhanced Core Fund changed its name on September 26, 2005 to Columbia Large Cap Enhanced Core Fund.

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The Fund

As described below, Thermostat's portfolio manager will have authority to review the Portfolio Funds and the relative allocation percentages among the stock funds and among the bond funds and to make any changes considered appropriate.

Thermostat is advised by Columbia Wanger Asset Management, L.P. (CWAM or the adviser). Each of the Portfolio Funds is managed by CWAM or an affiliate of CWAM. The Fund will not pay any sales load on its purchases of shares of the Portfolio Funds.

On an annual basis, or on an "emergency" basis if necessary, the portfolio manager reviews the structure, allocation percentages and Portfolio Funds of Thermostat and makes any changes considered appropriate. The portfolio manager typically addresses the following questions:

  Should the stock-bond allocation table be revised? (perhaps because the stock market has made a long-term move outside of the 750-1700 S&P 500 bands)

  Should there be a change in the Portfolio Funds in which Thermostat invests, or should there be a change in the percentage allocations among the stock funds or the bond funds? (perhaps because of a change of portfolio managers, change of investment style or reorganization of a Portfolio Fund)

Any changes by the portfolio manager are expected to be infrequent.

The S&P 500 is a broad market-weighted average of 500 widely-held large capitalization U.S. stocks.

The investment objectives and strategies of the current Portfolio Funds are described below:

Additional strategies that are not principal investment strategies and the risks associated with them are described on page 32 under "Other Investment Strategies and Risks."

Columbia Acorn Fund, Class Z (Acorn^® Fund)

Acorn Fund seeks to provide long-term growth of capital.

Acorn Fund generally invests in the stocks of small- and medium-sized companies. The Fund generally invests in the stocks of companies with market capitalizations of less than $5 billion at the time of initial purchase. As long as a stock continues to meet the Fund's other investment criteria, the Fund may choose to hold the stock even if it grows beyond an arbitrary capitalization limit.

Acorn Fund believes that these smaller companies, which are not as well known by financial analysts, may offer higher return potential than the stocks of larger companies.

Acorn Fund typically looks for companies with:

•  A strong business franchise that offers growth potential.

•  Products and services that give a company a competitive advantage.

•  A stock price the Fund's adviser believes is reasonable relative to the assets and earning power of the company.

Acorn Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its assets in companies outside the United States in developed markets (for example, Japan, Canada and the United Kingdom) and emerging markets (for example, Mexico, Brazil and Korea).

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The Fund

Columbia Acorn Select, Class Z (Acorn Select^SM)

Acorn Select seeks long-term growth of capital.

Acorn Select generally invests in the stocks of U.S. companies. The Fund is a non-diversified fund that takes advantage of its adviser's research and stock-picking capabilities to invest in a limited number of companies (between 20-40) with market capitalizations under $20 billion at the time of initial purchase, offering the potential to provide above-average growth over time.

Acorn Select believes that companies within this capitalization range are not as well known by financial analysts as the largest companies, and may offer higher return potential than the stocks of companies with capitalizations above $20 billion.

Acorn Select typically looks for companies with:

•  A strong business franchise that offers growth potential.

•  Products and services that give a company a competitive advantage.

•  A stock price the Fund's adviser believes is reasonable relative to the assets and earning power of the company.

Although Acorn Select does not buy securities with a short-term view, there is no restriction on the length of time the Fund must hold a security. To the extent the Fund buys and sells securities frequently, its transaction costs will be higher (which may adversely affect the Fund's performance) and it may realize additional capital gains.

The Fund invests the majority of its assets in U.S. companies, but also may invest up to 25% of its assets in companies outside the United States in developed markets (for example, Japan, Canada and the United Kingdom) and emerging markets (for example, Mexico, Brazil and Korea).

Columbia Marsico Growth Fund, Class Z (Marsico Growth Fund)

Marsico Growth Fund seeks long-term growth of capital.

Marsico Growth Funds invests all of its assets in Columbia Marsico Growth Master Portfolio (the Master Portfolio). The Master Portfolio has the same investment objective as Marsico Growth Fund.

The Master Portfolio invests primarily in equity securities of large-capitalization companies with a market capitalization of $4 billion or more that are selected for their growth potential. It generally holds a core position of between 35 and 50 common stocks. It may hold up to 25% of its assets in foreign securities.

The Master Portfolio may also invest in securities that aren't part of its principal investment strategies, but it won't hold more than 10% of its assets in any one type of these securities.

In selecting investments for the Master Portfolio, the investment adviser uses an approach that combines "top-down" macroeconomic analysis with "bottom-up" stock selection.

The "top-down" approach may take into consideration macroeconomic factors such as, without limitation, interest rates, inflation, demographics, the regulatory environment and the global competitive landscape. In addition, the investment adviser may also examine other factors that may include, without limitation, the most attractive global investment opportunities, industry consolidation, and the sustainability of financial trends observed. As a result of the "top-down" analysis, the investment adviser seeks to identify sectors, industries and companies that may benefit from the overall trends the investment adviser has observed.

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The Fund

The investment adviser then looks for individual companies or securities with earnings growth potential that may not be recognized by the market at large. In determining whether a particular company or security may be a suitable investment, the investment adviser may focus on any of a number of different attributes that may include, without limitation, the company's specific market expertise or dominance; its franchise durability and pricing power; solid fundamentals (e.g., a strong balance sheet, improving returns on equity, the ability to generate free cash flow, apparent use of conservative accounting standards and transparent financial disclosure); strong and ethical management; commitment to shareholder interests; reasonable valuations in the context of projected growth rates; and other indications that a company or security may be an attractive investment prospect.

This process is called "bottom-up" stock selection.

As part of this fundamental, "bottom-up" research, the investment adviser may visit with various levels of a company's management, as well as with its customers and (as relevant) suppliers, distributors and competitors. The investment adviser also may prepare detailed earnings and cash flow models of companies. These models may assist the investment adviser in projecting potential earnings growth and other important company financial characteristics under different scenarios. Each model is typically customized to follow a particular company and is generally intended to replicate and describe a company's past, present and potential future performance. The models may include quantitative information and detailed narratives that reflect updated interpretations of corporate data and company and industry developments.

The investment adviser may reduce or sell investments in portfolio companies if, in the opinion of the investment adviser, a company's fundamentals change substantially, its stock price appreciates excessively in relation to fundamental earnings growth prospects, the company appears not to realize its growth potential, or there are more attractive investment opportunities elsewhere. The Master Portfolio's core investments generally are comprised of established companies and securities that exhibit growth characteristics. However, the Master Portfolio also may typically include companies with more aggressive growth characteristics and companies undergoing significant changes: e.g., the introduction of a new product line, the appointment of a new management team, or an acquisition.

Marsico Growth Fund could withdraw its entire investment from the Master Portfolio if it believes it's in the best interests of the Fund to do so (for example, if the Master Portfolio changed its investment objective). It is unlikely that this would happen, but if it did, Marsico Growth Fund's portfolio could be less diversified and therefore less liquid, and expenses could increase. Marsico Growth Fund might also have to pay brokerage, tax or other charges.

Columbia Acorn International, Class Z (Acorn International^®)

Acorn International seeks to provide long-term growth of capital.

Acorn International generally invests in stocks of non-U.S. small- and medium-sized companies. The Fund generally invests in the stocks of companies based outside the United States with market capitalizations of less than $5 billion at the time of initial purchase. As long as a stock continues to meet the Fund's other investment criteria, the Fund may choose to hold the stock even if it grows beyond an arbitrary capitalization limit.

Acorn International believes that smaller companies, predominantly outside the United States, that are not as well known by financial analysts, may offer higher return potential than the stocks of larger companies.

Acorn International typically looks for companies with:

•  A strong business franchise that offers growth potential.

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The Fund

•  Products and services that give the company a competitive advantage.

•  A stock price the Fund's investment adviser believes is reasonable relative to the assets and earning power of the company.

Acorn International is an international fund and invests the majority (under normal market conditions, at least 75%) of its total assets in the stocks of foreign companies based in developed markets (for example, Japan, Canada and the United Kingdom) and emerging markets (for example, Mexico, Brazil and Korea).

Columbia Dividend Income Fund, Class Z (Dividend Income Fund)

Dividend Income Fund seeks current income and capital appreciation.

Under normal market conditions, Dividend Income Fund invests at least 80% of its net assets (plus any borrowings for investment purposes) in a diversified portfolio of income-producing (dividend-paying) equity securities, which will consist primarily of common stocks but may also include preferred stocks and convertible securities. The Fund's investment adviser looks for investments that it believes offer prospects for dividend growth and capital appreciation.

The Fund generally will emphasize value stocks, but may purchase growth securities when such securities pay dividends or the adviser believes such securities have particularly good prospects for capital appreciation. In addition to equity securities, the Fund may also invest up to 20% of its net assets in debt securities, including lower-quality debt securities. The Fund may invest up to 20% of its net assets in securities of foreign issuers.

At times, the investment adviser may determine that adverse market conditions make it desirable to suspend temporarily the Fund's normal investment activities. During such times, the Fund may, but is not required to, invest in cash or high-quality, short-term debt securities, without limit. Taking a temporary defensive position may prevent the Fund from achieving its investment goal.

Columbia Large Cap Enhanced Core Fund, Class Z (Core Fund)

Core Fund seeks, over the long term, to provide a total return that (before fees and expenses) exceeds the total return of the S&P 500 Index.

Under normal circumstances, Core Fund will invest at least 80% of its assets in a portfolio consisting of common stocks that are included in the S&P 500 Index, convertible securities that are convertible into stocks included in that index, and other derivatives whose economic returns are, by design, closely equivalent to the returns of the S&P 500 Index or its components. The S&P 500 Index is an unmanaged index of 500 widely held common stocks, and is not available for investment.

The portfolio manager tries to maintain a portfolio that matches the risk characteristics of the S&P 500 Index. The portfolio manager will, from time to time, vary the number and percentages of the Fund's holdings to try to provide higher returns than the S&P 500 Index and to reduce the risk of underperforming the index over time. The Fund generally holds fewer stocks than the index, and may hold securities that are not in the index.

Columbia Federal Securities Fund, Class Z (Federal Securities Fund)

Federal Securities Fund seeks as high a level of current income and total return as is consistent with prudent risk.

Under normal market conditions, Federal Securities Fund invests at least 80% of its net assets (plus any borrowings for investment purposes) in U.S. government securities, including U.S. treasuries and securities of

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The Fund

various U.S. government agencies and instrumentalities. Agency securities include mortgage-backed securities, which represent interests in pools of mortgages. Certain securities of U.S. government agencies and instrumentalities in which the Fund invests are neither issued nor guaranteed by the U.S. Treasury. Such securities may be supported by the ability to borrow from the U.S. Treasury or only by the credit of the issuing agency or instrumentality, and, as a result, may be subject to greater issuer risk than securities issued or guaranteed by the U.S. Treasury. The Fund may also invest up to 20% of its assets in corporate bonds or mortgage- or asset-backed securities that are issued by private entities. These securities must be rated investment grade by Moody's Investors Service, Inc. (Moody's), Standard & Poor's Corporation (S&P) and Fitch, Inc. (Fitch). The Fund has wide flexibility to vary its allocation among diffe rent types of U.S. government securities and the securities of non-governmental issuers based on the investment adviser's judgment of which types of securities will outperform the others. In selecting investments for the Fund, the adviser considers a security's expected income together with its potential to rise or fall in price.

Federal Securities Fund generally maintains a duration of greater than four and a half years and less than 10 years. As a result, the Fund's portfolio has market risks and an expected average life comparable to intermediate- to long-term bonds. The Fund's adviser may vary the Fund's duration depending on its forecast of interest rates and market conditions. For example, when interest rates are expected to increase, the adviser may shorten the duration, and vice versa.

Columbia Intermediate Bond Fund, Class Z (Intermediate Bond Fund)

Intermediate Bond Fund seeks its total return by pursuing current income and opportunities for capital appreciation.

As part of its investment strategy, Intermediate Bond Fund may buy and sell securities frequently. Such trading usually increases portfolio turnover rates, which usually increases the chance that the Fund will pay investors short-term capital gains (which are taxable at higher rates than long-term capital gains). Such trading may also result in higher brokerage commissions and other transaction costs and additional tax liability, which could reduce the Fund's returns.

Under normal circumstances, Intermediate Bond Fund invests at least 80% of its net assets (plus any borrowings for investment purposes) in bonds, including:

•  debt securities issued by the U.S. government, including U.S. treasury securities and agency securities (agency securities include certain mortgage-backed securities, which represent interests in pools of mortgages),

•  debt securities of corporations, and

•  mortgage-backed and asset-backed securities issued by private (non-governmental) entities.

Intermediate Bond Fund will invest at least 60% of its net assets in high-quality debt securities that are at the time of purchase:

•  rated at least A by S&P;

•  rated at least A by Moody's;

•  given a comparable rating by another nationally recognized rating agency; or

•  unrated securities that the Fund's adviser believes to be of comparable quality.

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The Fund

Intermediate Bond Fund may invest up to 20% of its net assets in lower-rated debt securities. These securities are sometimes referred to as "junk bonds" and are at the time of purchase:

•  rated below BBB by S&P;

•  rated below Baa by Moody's;

•  given a comparable rating by another nationally recognized rating agency; or

•  unrated securities that the Fund's adviser believes to be of comparable quality.

Normally, Intermediate Bond Fund expects to maintain a dollar-weighted average effective maturity of three to 10 years. The Fund seeks to achieve capital appreciation through purchasing bonds that increase in market value. In addition, to a limited extent, the Fund may seek capital appreciation by using hedging techniques such as futures and options.

Intermediate Bond Fund's adviser has wide flexibility to vary the allocation among different types of debt securities based on its judgment of which types of securities will outperform the others.

Columbia Conservative High Yield Fund, Class Z (High Yield Fund)

High Yield Fund seeks a high level of income, with capital appreciation as a secondary goal.

High Yield Fund pursues its objective by investing in non-investment-grade corporate debt securities, commonly referred to as "junk" or "high-yield" bonds. Normally, the Fund will invest at least 80% of its assets (plus any borrowings for investment purposes) in bonds rated Ba or B by Moody's or BB or B by S&P. No more than 10% of the Fund's assets will be invested in bonds rated Caa by Moody's or CCC by S&P, and no Fund assets will be invested in bonds below these grades. By focusing on higher quality junk bonds, the Fund seeks access to higher yielding bonds without assuming all the risk associated with the broader junk bond market.

PRINCIPAL INVESTMENT RISKS

The principal risks of investing in the Fund are described below. The value of an investment in the Fund is based primarily on the performance of the Portfolio Funds and the allocation of the Fund's assets among them. There are many circumstances (including additional risks that are not described here) that could prevent the Fund from achieving its investment goal. You may lose money by investing in the Fund.

Management risk. Management risk means that the adviser's investment decisions might produce losses or cause the Fund to underperform when compared to other funds with a similar investment goal. The Fund does not have the ability to affect how the portfolio managers of the Portfolio Funds manage those funds.

Market risk. Market risk means that security prices in a market, sector or industry may fall, reducing the value of your investment. Because of management and market risk, there is no guarantee that the Fund will achieve its investment goal or perform favorably among comparable funds.

Interest rate risk. Since the Fund may invest in bond Portfolio Funds, it is subject to interest rate risk. This is the risk of a change in the price of a bond when prevailing interest rates increase or decline. In general, if interest rates rise, bond prices fall, and if interest rates fall, bond prices rise. Changes in the values of bonds usually will not affect the amount of income the Fund receives from them but will affect the value of the Fund's shares. Interest rate risk is generally greater for bonds with longer maturities.

Issuer risk. Because a Portfolio Fund may invest in debt securities issued or supported by private entities, including corporate bonds and mortgage-backed and asset-backed securities, the Fund is subject to issuer risk.

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The Fund

Issuer risk is the possibility that changes in the financial condition of the issuer of a security, changes in general economic conditions or changes in economic conditions that affect the issuer may impact its actual or perceived willingness or ability to make timely payments of interest or principal. This could result in a decrease in the price of the security and in some cases a decrease in income.

Credit risk. Credit risk is the possibility that changes in the obligated entity's financial condition, changes in general economic conditions, or changes in economic conditions that affect the obligated entity, may impact the obligated entity's actual or perceived willingness or ability to make timely payments of interest or principal. This could result in a decrease in the price of the security and, in some cases, a decrease in income. Bonds that are backed by an issuer's taxing authority, including general obligation bonds, may be vulnerable to legal limits on a government's power to raise revenue or increase taxes. These bonds may depend for payment on legislative appropriation and/or aid from other governments. Other municipal bonds, known as revenue obligations, are payable from revenues earned by a particular project or other revenue source. So me revenue obligations are backed by private companies, some are asset-backed securities, such as bonds backed by mortgage payments, and some are for municipally owned utilities, such as water or sewer systems. Revenue obligations are subject to greater risk of default than general obligation bonds because investors can look only to the revenue generated by the project, assets, or private company backing the project, rather than to the taxing power of the state or local government issuer of the bonds.

Structure risk and prepayment risk. Structure risk is the risk that an event will occur (such as a security being prepaid or called) that alters the security's cash flows. Prepayment risk is a particular type of structure risk that is associated with investments in asset-backed and mortgage-backed securities. With respect to investments in mortgage-backed securities, prepayment risk is the possibility that, as prevailing interest rates fall, homeowners are more likely to refinance their home mortgages. When mortgages are refinanced, the principal on mortgage-backed securities is paid earlier than expected. In an environment of declining interest rates, asset-backed and mortgage-backed securities may offer less potential for gain than other debt securities. During periods of rising interest rates, asset-backed and mortgage-backed securities have a high risk of declining in price because the declining prepayment rates effectively increase the expected life of the security. In addition, the potential impact of prepayment on the price of an asset-backed and mortgage-backed security may be difficult to predict and result in greater volatility.

Lower-rated debt securities. Lower-rated debt securities, commonly referred to as "junk bonds," involve greater risk of loss due to credit deterioration and are less liquid, especially during periods of economic uncertainty or change, than higher quality debt securities. Lower-rated debt securities generally have a higher risk that the issuer of the security may default and not make payment of interest or principal.

Medium-quality debt securities. Medium-quality debt securities, although considered investment grade, may have some speculative characteristics.

Equity risk. Since the Fund invests in equity Portfolio Funds, it is subject to equity risk. This is the risk that stock prices will fall over short or extended periods of time. Although the stock market has historically outperformed other asset classes over the long term, the stock market tends to move in cycles. Individual stock prices may fluctuate drastically from day to day and may underperform other asset classes over an extended period of time. Individual companies may report poor results or be negatively affected by industry and/or economic trends and developments. The prices of securities issued by such companies may suffer a decline in response. These price movements may result from factors affecting individual companies, industries or the securities market as a whole.

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The Fund

Value stocks. Value stocks are securities of companies that may have experienced adverse business or industry developments or may be subject to special risks that have caused the stocks to be out of favor and, in the adviser's opinion, undervalued. If the adviser's assessment of a company's prospects is wrong, the price of the company's stock may fall, or may not approach the value the adviser has placed on it.

Growth stocks. Because some of the Portfolio Funds invest in growth stocks, the Fund is subject to the risk that growth stocks may be out of favor with investors for an extended period of time. Growth stocks are stocks of companies believed to have above-average potential for growth in revenue and earnings. Prices of growth stocks may be more sensitive to changes in current or expected earnings than the prices of other stocks. Growth stocks may not perform as well as value stocks or the stock market in general.

Market trends. The Fund is also subject to the risk that the adviser's decisions regarding asset classes and Portfolio Funds will not anticipate market trends successfully. For example, weighting Portfolio Funds that invest in common stocks too heavily during a stock market decline may result in a failure to preserve capital. Conversely, investing too heavily in Portfolio Funds that invest in bonds during a period of stock market appreciation may result in lower total return. Of course, the risks associated with investing in the Fund will vary depending upon how the assets are allocated among Portfolio Funds.

Management has no control over the portfolio managers or investment decisions of the Portfolio Funds. However, decisions made by the Portfolio Funds' managers will have a significant effect on a Fund's performance.

Affiliated fund risk. In managing the Fund, the portfolio manager will have authority to change the Portfolio Funds in which Thermostat invests or to change the percentage allocations among the stock funds or the bond funds. Since different Portfolio Funds pay different rates of management fees to CWAM or its affiliates, CWAM may have a conflict of interest selecting the Portfolio Funds or in determining the relative percentage allocations among Portfolio Funds.

Sector risk. Sector risk is inherent in the Portfolio Funds' investment strategies. Companies that are in different but closely related industries are sometimes described as being in the same broad economic sector. The values of stocks of different companies in a market sector may be similarly affected by particular economic or market events. Although the Fund does not intend to focus on any particular sector, at times the Portfolio Funds may have a significant portion of their assets invested in a particular sector.

Foreign securities. Foreign securities are subject to special risks. Foreign markets can be extremely volatile. Fluctuations in currency exchange rates may impact the dollar value of foreign securities denominated in foreign currencies and U.S. dollars, without a change in the intrinsic value of those securities. The liquidity of foreign securities may be more limited than that of domestic securities, which means that a Portfolio Fund may, at times, be unable to sell foreign securities at desirable prices. Brokerage commissions, custodial fees and other fees are generally higher for foreign investments. The Fund may have limited legal recourse in the event of default with respect to certain debt securities issued by foreign governments. In addition, foreign governments may impose withholding taxes that would reduce the amount of income and capital gai ns available to distribute to shareholders. Other risks include possible delays in the settlement of transactions or in the notification of income; less publicly available information about companies; the impact of political, social or diplomatic events; possible seizure, expropriation or nationalization of the company or its assets; and possible imposition of currency exchange controls.

Emerging markets. Investments in emerging markets are subject to additional risk. The risks of foreign investments are typically increased in less developed countries, which are sometimes referred to as emerging

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The Fund

markets. For example, political and economic structures in these countries may be new and developing rapidly, which may cause instability. Their securities markets may be underdeveloped. These countries are also more likely to experience high levels of inflation, deflation or currency devaluations, which could hurt their economies and securities markets.

Small- or mid-cap companies. Small- or mid-cap companies may be more susceptible to market downturns, and their prices could be more volatile than large-cap companies. These companies are more likely than larger companies to have limited product lines, operating histories, markets or financial resources. They may depend heavily on a small management team and may trade less frequently, may trade in smaller volumes and may fluctuate more sharply in price than stocks of larger companies. In addition, such companies may not be widely followed by the investment community, which can lower the demand for their stocks.

Futures risk. Core Fund may use futures contracts periodically to manage liquidity. There is a risk that this could result in losses, reduce returns, increase transaction costs or increase the Fund's volatility.

Derivatives risk. The use of derivatives presents risks different from, and possibly greater than, the risks associated with investing directly in traditional securities. Among the risks presented are market risk, credit risk, management risk and liquidity risk. The use of derivatives can lead to losses because of adverse movements in the price or value of the underlying asset, index or rate, which may be magnified by certain features of the derivatives. These risks are heightened when the portfolio manager uses derivatives to enhance a Fund's return or as a substitute for a position or security, rather than solely to hedge (or offset) the risk of a position or security held by the Fund. The success of management's derivatives strategies will depend on its ability to assess and predict the impact of market or economic developments on the underlying as set, index or rate and the derivative itself, without the benefit of observing the performance of the derivative under all possible market conditions. Liquidity risk exists when a security cannot be purchased or sold at the time desired, or cannot be purchased or sold without adversely affecting the price. The portfolio manager is not required to utilize derivatives to reduce risks.

Investing in the Master Portfolio. Marsico Growth Fund invests in the Master Portfolio, in which other mutual funds and eligible investors can buy shares. All investors in the Master Portfolio invest under the same terms and conditions as Marsico Growth Fund and pay a proportionate share of the Master Portfolio's expenses. Other feeder funds that invest in the Master Portfolio may have different share prices and returns than Marsico Growth Fund because different feeder funds typically have varying sales charges, and ongoing administrative and other expenses.

Convertible securities. Convertible securities are securities that can be converted into common stock, such as certain debt securities and preferred stock. Convertible securities are subject to the usual risks associated with fixed income investments, such as interest rate risk and credit risk. In addition, because they react to changes in the value of the equity securities into which they will convert, convertible securities are also subject to market risk.

Market timers. Because Acorn International invests predominantly in foreign securities, it may be particularly susceptible to market timers. Market timers generally attempt to take advantage of the way a fund prices its shares by trading based on market information they expect will lead to a change in the fund's net asset value on the next pricing day. Market timing activity may be disruptive to fund management and, since a market timer's profits are effectively paid directly out of the fund's assets, may negatively impact the investment returns of other shareholders. Although Acorn International has adopted certain policies and methods intended to identify and discourage frequent trading based on this strategy, it cannot ensure that all such activity can be identified or terminated.

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The Fund

Portfolio turnover. The Fund may buy and sell shares of the Portfolio Funds frequently. This may result in more realized income and greater income taxes, and could increase the transaction costs of the Portfolio Funds.

An investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PORTFOLIO HOLDINGS DISCLOSURE

A description of the Fund's policies and procedures with respect to the disclosure of its portfolio securities is available in the Fund's Statement of Additional Information (SAI), which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611.

The Fund posts its complete portfolio holdings at as of month-end www.columbiafunds.com approximately 30-40 calendar days after such month-end. Additionally, the Fund discloses its top 15 month-end portfolio holdings at www.columbiafunds.com on or about 15 calendar days following such month-end.

Once posted, the above information will remain available on the website until at least the date on which the Fund files a Form N-CSR or Form N-Q for the period that includes the date as of which the information is current.

PERFORMANCE HISTORY

The bar chart below shows the Fund's performance by illustrating the Fund's calendar year total returns (before taxes) for its Class Z shares. The performance table following the bar chart shows how the Fund's average annual total returns for Class Z shares compare with broad measures of market performance for one year and the life of the share class. The chart and table are intended to illustrate some of the risks of investing in the Fund by showing the changes in the Fund's performance. All returns include the reinvestment of dividends and distributions. As with all mutual funds, past performance (before and after taxes) does not predict the Fund's future performance.

UNDERSTANDING PERFORMANCE

Calendar Year Total Returns show the Fund's Class Z share performance for each completed calendar year since the Fund commenced operations. Those returns include the effects of Fund expenses.

Average Annual Total Returns are a measure of the Fund's Class Z average performance over the past one-year and life of the share class. They include the effects of Fund expenses.

The Fund's average annual returns are compared to the S&P 500 Index, its benchmark with respect to equity securities, and the Lehman Brothers U.S. Credit Intermediate Bond Index, the intermediate component of the LehmanBrothers U.S. Credit Index, its benchmark with respect to debt securities, and the Lipper Flexible Portfolio Funds Index. The S&P 500 Index is a broad market-weighted average 500 widely-held large capitalization stocks. The Lehman Brothers U.S. Credit Index includes publicly issued U.S. corporate and foreign debentures and secured notes that meet specified maturity, liquidity and quality requirements. The Lipper Flexible Portfolio Funds Index is an equal dollar-weighted index of the 30 largest mutual funds within the Flexible Portfolio fund classification, as defined by Lipper. Unlike the Fund, indices are not in vestments, do not incur fees, expenses or taxes, and are not professionally managed.

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The Fund

Calendar Year Total Returns (Class Z)

For period shown in bar chart:
Best quarter: 2nd quarter 2003, +11.36%
Worst quarter: 1st quarter 2003, -2.11%

After tax returns are calculated using the highest historical individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on each investor's own tax situation and may differ from those shown. After-tax returns may not be relevant to investors who hold Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Average Annual Total Returns — for periods ended December 31, 2006

Share Class	1 Year		Life of the Share Class(1)
Class Z (%)
Return Before Taxes		10.86		11.51
Return After Taxes on Distributions		8.30		10.02
Return After Taxes on Distributions and Sale of Fund Shares		8.09		9.35
Indices
S&P 500 Index (%)		15.79		15.81	(2)
Lehman Brothers U.S. Credit Intermediate Bond Index (%)		4.49		4.68	(2)
Lipper Flexible Portfolio Funds Index (%)		12.77		13.38	(2)

(1)  The inception date for Class Z shares is September 25, 2002.

(2)  Performance information is from September 25, 2002.

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The Fund

YOUR EXPENSES

Expenses are one of several factors to consider before you invest in a mutual fund. The tables below describe the fees and expenses you may pay when you buy, hold and sell shares of the Fund.

UNDERSTANDING EXPENSES

Annual Fund Operating Expenses are paid by the Fund. They include management and administration fees and other expenses that generally include, but are not limited to, transfer agency, custody, and legal fees as well as costs related to state registration and printing of Fund documents. The specific fees and expenses that make up the Fund's other expenses will vary from time to time and may include fees or expenses not described here.

Shareholder Fees (commissions paid directly from your investment)

Maximum sales charge (load) on purchases (%) (as a percentage of the offering price)	None
Maximum deferred sales charge (load) on redemptions (%) (as a percentage of the lesser of purchase price or redemption price)	None
Redemption fee (%) (as a percentage of amount redeemed, if applicable)	None(1)

(1)  There is a $7.50 charge for wiring sale proceeds to your bank.

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The Fund

Annual Fund Operating Expenses (deducted from Fund assets)

Management fees(1) (%)	0.10
Distribution and service (12b-1) fees (%)	None
Other expenses(2) (%)	0.31
Total annual fund operating expenses (%)	0.41
Expense reimbursement (%)	(0.16	)
Net expense ratio(3) (%)	0.25
Acquired Fund (Portfolio Fund) fees and expenses(4) (%)	0.69
Net expense ratio including expenses of Portfolio Funds(5) (%)	0.94
Gross expense ratio including expenses of Portfolio Funds (%)	1.10

(1)  The Fund pays an investment advisory fee of 0.10%. In addition to the management fee, the Fund and the other funds of Columbia Acorn Trust (the "Trust") pay the adviser an administrative fee based on the average daily aggregate net assets of the Trust at the following annual rates: 0.05% of net assets up to $8 billion; 0.04% of the next $8 billion; and 0.03% of net assets in excess of $16 billion. Based on the Trust's average daily net assets as of December 31, 2006, the Administrative fee would be at a rate of 0.04% and is included in "Other expenses."

(2)  "Other expenses" have been restated to reflect contractual changes to the transfer agency fees paid by the Fund.

(3)  The Fund's adviser has contractually agreed to bear a portion of the Fund's expenses so that the Fund's ordinary operating expenses (excluding any distribution and service fees, interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies) do not exceed 0.25% annually of the average daily net assets for Class Z shares through April 30, 2008. The adviser will have the right to recoup expense reimbursement payments made to the Fund through December 31, 2007. This will be accomplished by the payment of an expense reimbursement fee by the Fund to the adviser computed and paid monthly, with a limitation that immediately after such payment the Fund's ordinary operating expenses (excluding any distribution and service fees, interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies) will not exceed 0.25% annually.

(4)  Represents fees and expenses associated with the Fund's investments in other investment companies.

(5)  Includes the fees and expenses incurred by the Fund directly and indirectly from the underlying Portfolio Funds in which the Fund invests. The ratios shown above are based on the average invested balance of the Portfolio Funds, based on the respective net expense ratios of the Portfolio Funds for their respective last annual or semiannual report. Based on this allocation, the Fund's estimated indirect annual expenses would have been 0.69%. The indirect expense ratio of the Fund may be higher or lower depending on the portion of the Fund's assets allocated to each Portfolio Fund from time to time. As a result, the amount shown is higher than the ratio of expenses to average net assets included in the section entitled "Financial Highlights," which reflects only those expenses paid directly by the Fund.

Example Expenses help you compare the cost of investing in the Fund to the cost of investing in other mutual funds. The table does not take into account any expense reduction arrangements discussed in the footnotes to the Annual Fund Operating Expenses table. It uses the following hypothetical conditions:

•  $10,000 initial investment

•  5% total return for each year

•  Fund operating expenses remain the same

•  Reinvestment of all dividends and distributions

Example Expenses⁽¹⁾ for a $10,000 investment (your actual costs may be higher or lower)

1 Year		3 Years		5 Years		10 Years
$	96	$	334	$	591	$	1,326

(1)  Includes the fees and expenses incurred by the Fund directly and indirectly from the underlying Portfolio Funds in which the Fund invests. The example expenses for the one year period reflect the contractual cap on expenses referred to in footnote (3), but this arrangement is not reflected in the example expenses for the second and third years of the three year period, the second through fifth years of the five year period, or the second through tenth years of the ten year period.

See Appendix B for additional hypothetical investment and expense information.

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HOW TO BUY SHARES

If you are an eligible investor (described on page 19), when the Fund receives your purchase request in "good form," your shares will be bought at the next calculated price. "Good form" means that the Fund's transfer agent has all information and documentation it deems necessary to effect your order. For example "good form" may mean that you have properly placed your order with Columbia Management Services, Inc. or your financial advisor or the Fund's transfer agent has received your completed application, including all necessary signatures. The Fund reserves the right to refuse a purchase order for any reason, including if the Fund believes that doing so would be in the best interest of the Fund and its shareholders. The USA PATRIOT Act may require us to obtain certain personal information from you that we will use to verify your identity. If you do not provide the information, we may not be able to open your account. If we are unable to verify your customer information, we reserve the right to close your account or take such other steps as we deem reasonable.

You or your financial advisor may acquire shares of the Fund for your account by exchanging shares you own in a different fund distributed by Columbia Management Distributors, Inc. for shares of the same class or Class A of the Fund at no additional cost. To exchange by telephone, call 1-800-422-3737. Please see "How to Exchange Shares" for more information.

Outlined below are the various options for buying shares:

Method	Instructions
Through your financial advisor	Your financial advisor can help you establish your account and buy Fund shares on your behalf. To receive the current trading day's price, your financial advisor must receive your request prior to the close of regular trading on the New York Stock Exchange (NYSE), usually 4:00 p.m. Eastern time. Your financial advisor may charge you fees for executing the purchase for you.
By check (new account)	For new accounts, send a completed application and check made payable to the Fund to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By check (existing account)	For existing accounts, fill out and return the additional investment stub included in your account statement, or send a letter of instruction including the name, Fund share class and account number with a check made payable to the Fund to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.
By exchange	You may acquire Fund shares for your account by exchanging shares you own in a different fund distributed by Columbia Management Distributors, Inc. for shares of the same class or Class A of the Fund at no additional cost. To exchange by telephone, call 1-800-422-3737. Please see "How to Exchange Shares" for more information.
By wire	You may purchase Fund shares by wiring money from your bank account to your Fund account. To wire funds to your Fund account, call 1-800-422-3737 for wiring instructions.
By electronic fundstransfer	You may purchase Fund shares by electronically transferring money from your bank account to your Fund account by calling 1-800-422-3737. An electronic funds transfer may take up to two business days to settle and be considered in "good form." You must set up this feature prior to your telephone request. Be sure to complete the appropriate section of the application for this feature.
Automatic investmentplan	You may make monthly or quarterly investments ($50 minimum) automatically from your bank account to your Fund account. You may select a pre-authorized amount to be sent via electronic funds transfer. Be sure to complete the appropriate section of the application for this feature.
Automated dollar costaveraging	You may purchase Fund shares for your account by exchanging $100 or more each month from another fund for shares of the same class of the Fund at no additional cost. Exchanges will continue so long as your fund balance is sufficient to complete the transfers. You may terminate your program or change the amount of the exchange (subject to the $100 minimum) by calling 1-800-345-6611. Be sure to complete the appropriate section of the account application for this feature.

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Your Account

Method	Instructions
By dividend diversification	You may automatically invest dividends distributed by another fund into the same class of Fund shares at no additional sales charge. There may be an additional sales charge if automatically investing dividends from a money market fund. To invest your other dividends in the Fund, call 1-800-345-6611.
Through the internet	You may purchase Fund shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet purchases. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

ELIGIBLE INVESTORS

Only certain eligible investors may purchase Class Z shares of the Fund (Eligible Investor), directly or by exchange. Please read the following section for a more detailed description of the eligibility requirements. The Eligible Investors described below are subject to different minimum initial investment requirements.

Eligibility for certain waivers, exemptions or share classes by new or existing investors may not be readily available or accessible through all intermediaries or all types of accounts offered by a broker-dealer, bank, third-party administrator or other financial institution (each commonly referred to as an "intermediary"). Accessibility of these waivers through a particular intermediary also may change at any time. If you believe you are eligible to purchase shares under a specific exemption, but are not permitted by your intermediary to do so, please contact your intermediary. You may be asked to provide information, including account statements and other records, regarding your eligibility.

Eligible Investors and their applicable investment minimums are as follows:

No minimum initial investment

•  Any group retirement plan, holding Fund shares in an omnibus manner, for which an intermediary or other entity provides services and is not compensated by the Funds for those services, other than payments for shareholder servicing or sub-accounting performed in place of the transfer agent.

•  Any person investing all or part of the proceeds of a distribution, rollover or transfer of assets into a Columbia Management Individual Retirement Account from any deferred compensation plan which was a shareholder of any of the funds of Columbia Acorn Trust (formerly named Liberty Acorn Trust) on September 29, 2000, in which the investor was a participant and through which the investor invested in one or more of the funds of Columbia Acorn Trust immediately prior to the distribution, transferor rollover.

$1,000 minimum initial investment (by purchase, exchange or transfer)

•  Any individual retirement account of an Eligible Investor; or

•  Any group retirement plan, not holding Fund shares in an omnibus manner, for which an intermediary or other entity provides services and is not compensated by the Fund for those services, other than compensation for shareholder servicing or sub-accounting performed in place of the transfer agent.

$2,500 minimum initial investment (by purchase, exchange or transfer)

•  Any shareholder (as well as any family member of a shareholder or person listed on an account registration for any account of the shareholder) of a fund distributed by Columbia Management Distributors, Inc. (CMD) (i) who holds Class Z shares; (ii) who holds shares issued upon conversion of

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Your Account

Primary A shares held prior to August 22, 2005; (iii) who holds Class A shares that were obtained by exchange of Class Z shares; or (iv) who holds no-load shares issued upon the merger of a fund distributed by CMD;

•  Any trustee or director (or family member of a trustee or director) of any fund distributed by CMD;

•  Any employee (or family member of an employee) of Bank of America Corporation or a subsidiary;

•  Any investor participating in an account offered by an intermediary or other entity that provides services to such an account, is paid an asset-based fee by the investor and is not compensated by the Funds for those services, other than payments for shareholder servicing or sub-accounting performed in place of the Fund's transfer agent (each investor purchasing through an intermediary must independently satisfy the minimum investment requirement noted above);

•  Any client of Bank of America Corporation or a subsidiary purchasing through an asset management company, trust, fiduciary, retirement plan administration or similar arrangement with Bank of America Corporation or the subsidiary;

•  Any investor purchasing through a Columbia Management state tuition plan organized under Section 529 of the Internal Revenue Code;

•  Any institutional investor which is a corporation, partnership, trust, foundation, endowment, institution, government entity, or similar organization; which meets the respective qualifications for an accredited investor, as defined under the Securities Act of 1933; or

•  Certain financial institutions and intermediaries, such as insurance companies, trust companies, banks, endowments, investment companies or foundations, purchasing shares for its own account, including Bank of America Corporation, its affiliates, or subsidiaries.

The investment minimum is applied at the class level. For group retirement plans, the investment minimum is determined based on the amount of the plan's investment rather than that of its individual participants. The Fund may establish exclusions from the investment minimum from time to time that it deems appropriate and consistent with the interests of shareholders. Please see the Statement of Additional Information for details on these exclusions.

The Fund reserves the right to change the criteria for eligible investors and the investment minimums. No minimum investment applies to accounts participating in the automatic investment plan; however, each investment requires a $50 minimum purchase. The Fund also reserves the right to refuse a purchase order for any reason, including if it believes that doing so would be in the best interest of the Fund and its shareholders. Finally, pursuant to the Trust's Agreement and Declaration of Trust, the Fund reserves the right to redeem your shares if your account falls below the minimum investment requirements.

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Your Account

SALES CHARGES (COMMISSIONS)

Your purchases of Class Z shares are at net asset value, which is the value of a Class Z share excluding any sales charge. Class Z shares are not subject to an initial sales charge when purchased, or a contingent deferred sales charge when sold.

CHOOSING A SHARE CLASS

The Fund offers one class of shares in this prospectus — Class Z.

The Fund also offers three additional classes of shares — Class A, B and C shares are available through a separate prospectus. Each other share class has its own sales charge and expense structure.

Broker-dealers, investment advisers or financial planners selling mutual fund shares may offer their clients more than one class of shares in a fund with different pricing options. This allows you and your financial advisor to choose among different types of sales charges and different levels of ongoing operating expenses, depending on the investment programs your financial advisor offers. Investors should consider carefully any separate transactions and other fees charged by these programs in connection with investing in any available share class before selecting a share class.

Determining which share class is best for you depends on the dollar amount you are investing and the number of years for which you are willing to invest. Based on your personal situation, your financial advisor can help you decide which class of shares makes the most sense for you. In general, anyone who is eligible to purchase Class Z shares, which do not incur Rule 12b-1 fees or sales charges, should do so in preference over other classes.

If you purchase Class Z shares of the Fund through certain intermediaries, they may charge a fee for their services. They may also place limits on your ability to use services the Fund offers. There are no sales charges or limitations if you purchase shares directly from the Fund, except as described in this prospectus.

If an intermediary is an agent or designee of the Fund, orders are processed at the net asset value next calculated after the intermediary receives the order. The intermediary must segregate any orders it receives after the close of regular trading on the NYSE and transmit those orders separately for execution at the net asset value next determined.

HOW TO EXCHANGE SHARES

You may exchange your shares for Class Z or Class A (only if Class Z is not offered) shares of another fund distributed by CMD at net asset value. Unless your account is part of a tax-deferred retirement plan, an exchange is a taxable event, and you may recognize a gain or a loss for tax purposes. The Fund may terminate your exchange privilege if the adviser determines that your exchange activity is likely to adversely impact its ability to manage the Fund. See "Fund Policy on Trading of Fund Shares" for the Fund's policy. To exchange by telephone, call 1-800-422-3737. Please have your account and taxpayer identification numbers available when calling.

You also may exchange your shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet exchanges. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

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Your Account

HOW TO SELL SHARES

You may sell shares of the Fund on any regular business day that the NYSE is open. When the Fund receives your sales request in "good form," shares will be sold at the next calculated price. "Good form" means the Fund's transfer agent has all information and documentation it deems necessary to effect your order. For example, when selling shares by letter of instruction, "good form" means (i) your letter has complete instructions, the proper signatures and Medallion Signature Guarantees, and (ii) any other required documents are attached. For additional documents required for sales by corporations, agents, fiduciaries, surviving joint owners, and other legal entities please call 1-800-345-6611. Retirement plan accounts have special requirements; please call 1-800-799-6611 for more information.

The Fund will generally send proceeds from the sale to you within seven days (usually on the next business day after your request is received in "good form"). However, if you purchased your shares by check, the Fund may delay sending the proceeds from the sale of your shares for up to 10 days after your purchase to protect against checks that are returned. No interest will be paid on uncashed redemption checks. Redemption proceeds may be paid in securities, rather than cash, under certain circumstances. For more information, see the paragraph "Non-Cash Redemptions" under the section "How to Sell Shares" in the SAI.

During the 90-day period for any shareholder, the Fund is obligated to redeem shares solely in cash up to the lesser of $25,000 or 1% of the Fund's net assets. Redemptions in excess of these limits will normally be paid in cash, but may be paid wholly or partly by an in-kind distribution of securities.

Outlined below are the various options for selling shares:

Method	Instructions
Through your financialadvisor	You may call your financial advisor to place your sell order. To receive the current trading day's price, your financial advisor must receive your request prior to the close of regular trading on the NYSE, usually 4:00 p.m. Eastern time. Your financial advisor may charge you fees for executing a redemption for you.
By exchange	You or your financial advisor may sell Fund shares by exchanging from the Fund into Class Z shares or Class A (only if Class Z is not offered) shares of another fund distributed by Columbia Management Distributors, Inc. at no additional cost. To exchange by telephone, call 1-800-422-3737.
By telephone	You or your financial advisor may sell Fund shares by telephone and request that a check be sent to your address of record by calling 1-800-422-3737, unless you have notified the Fund of an address change within the previous 30 days. The dollar limit for telephone sales is $100,000 in a 30-day period. You do not need to set up this feature in advance of your call. Certain restrictions apply to retirement accounts. For details, call 1-800-799-7526.
By mail	You may send a signed letter of instruction to the address below. In your letter of instruction, note the Fund's name, share class, account number, and the dollar value or number of shares you wish to sell. All account owners must sign the letter. Signatures must be guaranteed by either a bank, a member firm of a national stock exchange or another eligible guarantor that participates in the Medallion Signature Guarantee program for amounts over $100,000 or for alternate payee or mailing instructions. Additional documentation is required for sales by corporations, agents, fiduciaries, surviving joint owners and individual retirement account owners. For details, call 1-800-345-6611. Mail your letter of instruction to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA02266-8081.
By wire	You may sell Fund shares and request that the proceeds be wired to your bank. You must set up this feature prior to your request. Be sure to complete the appropriate section of the account application for this feature. Generally, the value of your redemption must be at least equal to $500 in order to have the sale proceeds wired to your bank. There is a $7.50 charge for wiring sale proceeds to your bank. (The transfer agent may waive this fee for omnibus and nominee accounts.) Your bank may charge additional fees for such wire transfer.

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Your Account

Method	Instructions
By systematic withdrawal plan	You may automatically sell a specified dollar amount or percentage of your account on a monthly, quarterly or semiannual basis and have the proceeds sent to you if your account balance is at least $5,000. The $5,000 minimum account balance requirement has been waived for wrap accounts. All dividend and capital gains distributions must be reinvested. Be sure to complete the appropriate section of the account application for this feature.
By electronic fundstransfer	You may sell Fund shares and request that the proceeds be electronically transferred to your bank. Proceeds may take up to two business days to be received by your bank. You must set up this feature prior to your request. Be sure to complete the appropriate section of the account application for this feature.
Through the internet	You may sell Fund shares through the internet. You will be required to accept the terms of an online agreement and to use a password in order to make internet redemptions. The transfer agent has procedures in place to authenticate electronic instructions given via the internet. For more information on internet transactions, or to sign up for internet transactions, please call 1-800-345-6611.

FUND POLICY ON TRADING OF FUND SHARES

The interests of the Fund's long-term shareholders may be adversely affected by certain short-term trading activity by Fund shareholders. Such short-term trading activity, when excessive, has the potential to interfere with efficient portfolio management, generate transaction and other costs, dilute the value of Fund shares held by long-term shareholders and have other adverse effects on the Fund. This type of excessive short-term trading activity is referred to herein as "market timing." For purposes of this section "Columbia Funds" are the Columbia, Columbia Acorn and Wanger Advisors Trust families of mutual funds. The Columbia Funds are not intended as vehicles for market timing. The Board of Trustees of the Fund has adopted the Policies and Procedures set forth below with respect to frequent trading of Fund shares.

The Fund, directly and through its agents, takes various steps designed to deter and curtail market timing. For example, if the Fund detects that any shareholder has conducted two "round trips" (as defined below) in the Fund in any 28-day period, except as noted below with respect to orders received through omnibus accounts, the Fund will reject the shareholder's future purchase orders, including exchange purchase orders, involving any Columbia fund (other than a money market fund). In addition, if the Fund determines that any person, group or account has engaged in any type of market timing activity (independent of the two-round-trip limit), the Fund may, in its discretion, reject future purchase orders by the person, group or account, including exchange purchase orders, involving the same or any other Columbia fund, and also retains the right to modify these market timing policies at any time without prior notice.

The rights of shareholders to redeem shares of the Fund are not affected by any of the limits mentioned above. However, certain funds (other than the Fund) impose a redemption fee on the proceeds of fund shares that are redeemed or exchanged within 60 days of their purchase.

For these purposes, a "round trip" is a purchase by any means into a Columbia fund followed by a redemption, of any amount, by any means out of the same Columbia fund. Under this definition, an exchange into the Fund followed by an exchange out of the Fund is treated as a single round trip. Also for these purposes, where known, accounts under common ownership or control generally will be counted together. Accounts maintained or managed by a common intermediary, such as an adviser, selling agent or trust department, generally will not be considered to be under common ownership or control.

Purchases, redemptions and exchanges made through the Columbia Funds' Automatic Investment Plan, Systematic Withdrawal Plan or similar automated plans are not subject to the two-round-trip limit. Purchases, redemptions and exchanges made by Thermostat Fund are also not subject to the two round-trip limit. The two-round-trip limit may be modified for, or may not be applied to, accounts held by certain retirement plans to

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conform to plan limits, considerations relating to the Employee Retirement Income Security Act of 1974 or regulations of the Department of Labor, and for certain asset allocation or wrap programs.

The practices and policies described above are intended to deter and curtail market timing in the Fund. However, there can be no assurance that these policies, individually or collectively, will be totally effective in this regard because of various factors. In particular, a substantial portion of purchase, redemption and exchange orders are received through omnibus accounts. Omnibus accounts, in which shares are held in the name of an intermediary on behalf of multiple beneficial owners, are a common form of holding shares among financial intermediaries and retirement plans. The Fund typically is not able to identify trading by a particular beneficial owner through an omnibus account, which may make it difficult or impossible to determine if a particular account is engaged in. Consequently, there is the risk that the Fund may not be able to identify, deter or curtail certain marketing timing that occurs in the Fund, which may r esult in certain shareholders being able to market time the Fund while the shareholders in the Fund bear the burden of such activities.

Certain financial intermediaries, including certain retirement plan service providers whose clients include, among others, various retirement plans sponsored by Bank of America and its affiliates for the benefit of its employees (the "Bank of America retirement Plan service providers"), have different policies regarding monitoring and restricting market timing in the underlying beneficial owner accounts that they maintain through an omnibus account that may be more or less restrictive than the Fund practices discussed above. In particular, the Bank of America retirement Plan service providers permits the reinstatement of future purchase orders for shares of the Fund following various suspension periods. If an intermediary does not enforce the Fund's policy, the intermediary must either provide data transparency to Columbia Management or Columbia Management must determine that the intermediary's policy taken in its entirety provi des protections to Fund shareholders that are generally commensurate with the Fund privacy policy.

The Fund seeks to act in a manner that it believes is consistent with the best interests of Fund shareholders in making any judgments regarding market timing. Neither the Fund nor its agents shall be held liable for any loss resulting from rejected purchase orders or exchanges.

FINANCIAL INTERMEDIARY PAYMENTS

The Fund's distributor, investment adviser or their affiliates may make payments, from their own resources, to certain financial intermediaries, including other Bank of America affiliates, for marketing support services. For purposes of this section the term "financial intermediary" includes any broker, dealer, bank, bank trust department, registered investment adviser, financial planner, retirement plan or other third-party administrator and any other institution having a selling, services or any similar agreement with the Fund's distributor, investment adviser or one of their affiliates. These payments are generally based upon one or more of the following factors: average net assets of the mutual funds distributed by the Fund's distributor attributable to that financial intermediary, gross sales of the mutual funds distributed by the Fund's distributor attributable to that financial intermediary, reimbursement of ticket charge s (fees that a financial intermediary firm charges its representatives for effecting transactions in fund shares) or a negotiated lump sum payment.

While the financial arrangements may vary for each financial intermediary, the payments to any one financial intermediary are generally expected to be between 0.05% and 0.45% on an annual basis for payments based on average net assets of the Fund attributable to the financial intermediary, and between 0.10% and 0.25% on an annual basis for firms receiving a payment based on gross sales of the Fund attributable to the financial intermediary. The Fund's distributor, investment adviser or their affiliates may make payments in materially larger

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Your Account

amounts or on a basis materially different from those described above when dealing with other affiliates of Bank of America. Such increased payments to the other Bank of America affiliate may enable the other Bank of America affiliate to offset credits that it may provide to its customers in order to avoid having such customers pay fees to multiple Bank of America entities in connection with the customer's investment in the Fund.

Payments also may be made to certain financial intermediaries, including other Bank of America affiliates, that provide investor services to retirement plans and other investment programs to compensate financial intermediaries for services they provide to such programs, including, but not limited to, sub-accounting, sub-transfer agency, similar shareholder or participant recordkeeping, shareholder or participant reporting, or shareholder or participant transaction processing. These payments for investor servicing support vary by financial intermediary but generally are not expected, with certain limited exceptions, to exceed 0.45% of the total Fund assets for Class Z shares in the program on an annual basis.

As of October 1, 2006, the Trust's Board of Trustees has authorized the Fund to pay to any intermediary up to 0.05% of the average aggregate value of Fund shares in the intermediary's program on an annual basis for providing investor services. Charges of an intermediary in excess of that paid by the Fund will be borne by the Fund's distributor or its affiliates.

The Fund's distributor, investment adviser or their affiliates may make other payments or allow promotional incentives to financial intermediaries to the extent permitted by the rules of the Securities and Exchange Commission, the National Association of Securities Dealer's and by other applicable laws and regulations.

Amounts paid by the Fund's distributor, investment adviser or their affiliates are paid out of the distributor's, investment adviser's or their affiliates' own resources and do not increase the amount paid by you or the Fund. You can find further details about the payments made by the Fund's distributor, investment adviser or their affiliates and the services provided by financial intermediaries as well as a list of the financial intermediaries to which the Fund's distributor, investment adviser or their affiliates have agreed to make marketing support payments in the Fund's SAI, which can be obtained at www.columbiafunds.com or by calling 1-800-345-6611. Your financial intermediary may charge you fees or commissions in addition to those disclosed in this prospectus. You can ask y our financial intermediary for information about any payments it receives from the Fund's distributor, investment adviser and their affiliates and any services your financial intermediary provides, as well as fees and/or commissions it charges. In addition, depending on the financial arrangement in place at any particular time, a financial intermediary and its financial consultants also may have a financial incentive for recommending a particular fund or share class over others. You should consult with your financial adviser and review carefully any disclosure by the financial intermediary as to compensation received by your financial adviser.

OTHER INFORMATION ABOUT YOUR ACCOUNT

How the Fund's Share Price is Determined The price of a Fund's Class Z shares is based on their net asset value. The net asset value is determined at the close of regular trading on the NYSE, usually 4:00 p.m. Eastern time, on each business day that the NYSE is open for trading (typically Monday through Friday). Net asset value is not determined on days on which the NYSE is closed for trading.

When you request a transaction, it will be processed at the net asset value per share next determined after your request is received in "good form" by the distributor. In most cases, in order to receive that day's price, the Fund must receive your order before that day's transactions are processed. If you request a transaction through your financial advisor, your financial advisor must receive your order by the close of trading on the NYSE to receive that day's price.

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The Fund determines its net asset value for its Class Z shares by dividing total net assets attributable to Class Z shares by the number of outstanding Class Z shares. In determining the net asset value, the Fund must determine the value of each security in its portfolio at the close of each trading day. Because some of the Portfolio Funds hold securities that are traded on foreign exchanges, the value of the Portfolio Funds' securities may change on days when shareholders will not be able to buy or sell Fund shares. This will affect the Fund's net asset value on the day it is next determined. Securities for which market quotations are available are valued each day at the current market value. However, where market quotations are unavailable, or when the Portfolio Fund's adviser believes that subsequent events have made them unreliable, the Fund may use other data to determine the fair value of the securities.

The Fund has retained an independent statistical fair value pricing service to assist in the fair valuation process for securities principally traded in a foreign market in order to adjust for possible changes in value that may occur between the close of the foreign exchange and the time at which Fund shares are priced. The use of an independent fair value pricing service is intended to and may decrease the opportunities for time zone arbitrage transactions. There can be no assurance that the use of an independent fair value pricing service will successfully decrease arbitrage opportunities. If a security is valued at a "fair value," that value may be different from the last quoted market price for the security.

You can find the daily prices of some share classes for the Fund in most daily newspapers under the heading of "Columbia." You can find daily prices for all share classes by visiting www.columbiafunds.com.

Share Certificates Share certificates are not available for Class Z shares.

Dividends, Distributions, and Taxes The Fund has the potential to make the following distributions:

Types of Distributions

Dividends	Represents interest and dividends earned from securities held by the Fund, net of expenses incurred by the Fund.
Capital gains	Represents net long-term capital gains on sales of securities held for more than one year and net short-term capital gains, which are gains on sales of securities held for a one-year period or less.

Distribution Options The Fund distributes any dividends in June and December and any capital gains (including short-term capital gains) at least annually. You can choose one of the options listed in the table below for these distributions when you open your account. To change your distribution option call 1-800-345-6611.

If you do not indicate on your application or at the time your account is established your preference for handling distributions, the Fund will automatically reinvest all distributions in additional shares of the Fund.

UNDERSTANDING FUND DISTRIBUTIONS

The Fund may earn income from the securities it holds. The Fund also may realize capital gains or losses on sales of its securities. The Fund intends to distribute substantially all of its net investment income and capital gains to shareholders each year. As a shareholder, you are entitled to a portion of the Fund's income and capital gains based on the number of shares you own at the time these distributions are declared.

26

Your Account

Distribution Options

Reinvest all distributions in additional shares of the Fund

Reinvest all distributions in shares of another fund

Receive dividends in cash (see options below) and reinvest capital gains

Receive all distributions in cash (with one of the following options):

•  send the check to your address of record

•  send the check to a third-party address

•  transfer the money to your bank via electronic funds transfer

Distributions of $10 or less will automatically be reinvested in additional Fund shares. If you elect to receive distributions by check and the check is returned as undeliverable all subsequent distributions will be reinvested in additional shares of the Fund.

TaxesUnless you are an entity exempt from income tax or invest under a retirement account, regardless of whether you receive your distributions in cash or reinvest them in additional Fund shares, all Fund distributions are subject to federal income tax. Depending on where you live, distributions also may be subject to state and local income taxes.

The Fund intends to elect to be treated and to qualify each year as a regulated investment company. A regulated investment company is not subject to tax at the corporate level on income and gains from investments that are distributed to shareholders in accordance with applicable law. However, the Fund's failure to qualify as a regulated investment company could result in corporate level taxation, and consequently, a reduction in income available for distribution to shareholders.

In general, any distributions of dividends, interest and short-term capital gains (determined by how long the Fund held the investments that generated them) are taxable as ordinary income, unless such dividends are "qualified dividend income" (as defined in the Internal Revenue Code) eligible for a reduced rate of tax. Properly designated distributions of long-term capital gains (determined by how long the Fund held the investments that generated them) are generally taxable as such, regardless of how long you have held your Fund shares. You will be provided with information each year regarding the amount of ordinary income and capital gains distributed to you for the previous year and any portion of your distribution which is exempt from state and local taxes. Long-term capital gain rates have been reduced — in general, to 15% with lower rates applying to taxpayers in the 10% and 15% rate brackets — for taxable years b eginning before January 1, 2011. Distributions are taxable to you even if they are paid from income or gains earned by the Fund before you made your investment (and thus were included in the price you paid).

Income other than net capital gains received by the Fund from the Portfolio Funds (including dividends and distributions of short-term capital gains) will be distributed by the Fund (after deductions for expenses) and will be taxable to you as ordinary income, unless it is eligible to be treated as qualified dividend income. Because the Fund is an asset allocation fund and may realize taxable net short-term capital gains by selling shares of a Portfolio Fund in its portfolio with unrealized portfolio appreciation, investing in the Fund rather than directly in the Portfolio Fund may result in accelerated tax liability to you since the Fund must distribute its gains in accordance with the Internal Revenue Code.

Distributions of net capital gains received by the Fund from its Portfolio Funds, plus net long-term capital gains realized by the Fund from the purchase and sale of Portfolio Fund shares or other securities held by the Fund for more than one year, will be distributed by the Fund and will be taxable to you as long-term capital gains (even if

27

Your Account

you have held Fund shares for one year or less). If a shareholder who has received a capital gains distribution suffers a loss on the sale of his or her shares not more than six months after purchase, the loss will be treated as a long-term capital loss to the extent of the capital gains distribution received. Long-term capital gains, including distributions of net capital gains, are currently subject to a maximum federal tax rate of 15%. This rate is less than the maximum rate imposed on other types of taxable income. Capital gains also may be advantageous since, unlike ordinary income, they may be offset by capital losses.

For purposes of determining the character of income received by the Fund when a Portfolio Fund distributes net capital gains to the Fund, the Fund will treat the distribution as long-term capital gain, even if the Fund has held shares of the Portfolio Fund for one year or less. Any loss incurred by the Fund on the sale of that Portfolio Fund's shares held for six months or less, however, will be treated as a long-term capital loss to the extent of the net capital gain distribution.

High portfolio turnover may cause the Fund to realize short-term capital gains which, if realized and distributed by the Fund, may be taxable to shareholders as ordinary income. Distributions of long-term capital gains are generally taxable as such, regardless of how long you have held your Fund shares. You will be provided with information each year regarding the amount of ordinary income and capital gains distributed to you for the previous year and any portion of your distribution which is exempt from state and local taxes. Your investment in the Fund may have additional personal tax implications. Please consult your tax advisor about foreign, federal, state, local or other applicable tax laws.

In addition to the dividends and capital gains distributions made by the Fund, you may realize a capital gain or loss when selling or exchanging shares of the Fund. Such transactions also may be subject to federal, state and local income tax.

Board of Trustees

The Fund is governed by its Board of Trustees. More than 75% of the Fund's Trustees are independent, meaning that they have no affiliation with the adviser or the Funds, apart from their positions as Trustees and the personal investments they may have made as private individuals.

The independent Trustees bring backgrounds in business and the professions and academia to their task of working with the Funds' officers to establish the policies and oversee the activities of the Funds. Among the Trustees' responsibilities are selecting the investment adviser for the Funds; negotiating the advisory agreements; reviewing other contracts; approving investment policies; monitoring Fund operations, performance, and costs; and nominating or selecting new Trustees.

Each Trustee serves until his or her retirement, resignation, death or removal; or otherwise as specified in the Trust's organizational documents. It is expected that every five years the Trustees will call a meeting of shareholders to elect Trustees. A Trustee must retire at the end of the year in which he or she attains the age of 75. Any Trustee may be removed at a shareholders' meeting by a vote representing two-thirds of the net asset value of all shares of the Funds of the Trust. The mailing address for the Trustees and officers is 227 W. Monroe, Suite 3000, Chicago, Illinois 60606.

For more detailed information on the Board of Trustees, please refer to the SAI.

28

Managing the Fund

INVESTMENT ADVISER

Columbia Wanger Asset Management, L.P. (CWAM), located at 227 West Monroe Street, Suite 3000, Chicago, Illinois 60606, is the Fund's investment adviser and is responsible for the Fund's management, subject to oversight by the Fund's Board of Trustees. CWAM and its predecessor have managed mutual funds, including the Fund, since 1992. In its duties as investment adviser, CWAM runs the Fund's day-to-day business, including placing all orders for the purchase and sale of the Fund's portfolio securities.

CWAM was previously named Liberty Wanger Asset Management, L.P., and its predecessor was named Wanger Asset Management, L.P. (WAM). CWAM is a wholly owned subsidiary of Columbia Management Group, LLC, which in turn is an indirect wholly owned subsidiary of Bank of America Corporation. As of December 31, 2006 CWAM managed more than $27.1 billion in assets.

CWAM's advisory fee for managing the Fund in 2006 was 0.10% of the Fund's average daily net assets. CWAM also received an administrative fee from the Fund in 2006 of 0.04% of the Fund's average daily net assets. A discussion of the factors considered by the Fund's Board of Trustees in approving the Fund's investment advisory contract is included in the Fund's annual report to shareholders for the period ended December 31, 2006.

The Portfolio Funds are managed by CWAM and its affiliate Columbia Management Advisors, LLC, previously named Columbia Management Company (CMA). On April 1, 2003, Colonial Management Associates and Stein Roe & Farnham Incorporated and other affiliated investment adviser entities were merged with and into CMA. CMA assumed all of the business associated with each of the merged investment advisers. Like CWAM, CMA is owned by Columbia Management Group, LLC. CMA also may provide administrative and operational services to Thermostat.

PORTFOLIO MANAGER

The portfolio manager reviews on an infrequent basis the structure and allocation ranges of Thermostat and makes any changes considered appropriate.

Charles P. McQuaid

Lead portfolio manager

Charles McQuaid is president of the Trust and a member of the Trust's Board of Trustees. He has been president of CWAM since October 2003, chief investment officer of CWAM since October 2003, and was director of research at CWAM and its predecessor from July 1992 through December 2003. Mr. McQuaid has been a member of Columbia Acorn Fund's management team since 1978, co-managed Columbia Acorn Fund from 1995 through September 2003 and has been the Fund's lead portfolio manager since September 2003. He served as CWAM's interim director of international research from October 2003 to December 2004. Mr. McQuaid has been the president of Wanger Advisors Trust since 2003 and a trustee since September 2006. He also manages two domestic separate accounts and two offshore funds.

The Statement of Additional Information provides additional information about the portfolio manager's compensation, other accounts managed and ownership of securities in the Fund.

29

Managing the Fund

LEGAL PROCEEDINGS

The Trust, CWAM and the trustees of the Trust (collectively, the "Columbia defendants") are named as defendants in class and derivative complaints, which were consolidated in a Multi-District Action in the federal district court for the District of Maryland on February 20, 2004 (the "MDL Action"). These lawsuits contend that defendants permitted certain investors to market time their trades in certain Columbia Acorn Funds. The MDL Action is ongoing. All claims against the Trust and its independent trustees have been dismissed; however, the interested trustees of the Trust are still parties to MDL Action.

On March 21, 2005, a class action complaint was filed against the Trust in the Superior Court of the Commonwealth of Massachusetts seeking to rescind the contingent deferred sales charges assessed upon redemption of Class B shares of Columbia Acorn Funds due to the alleged market timing by certain shareholders of the Columbia Acorn Funds. In addition to the rescission of sales charges, plaintiffs seek recovery of actual damages, attorneys' fees and costs. The case has been transferred to the MDL Action in the federal district court of Maryland.

The Trust and CWAM are also defendants in a class action lawsuit, filed on November 13, 2003 in the Circuit Court of the Third Judicial Circuit, Madison County, Illinois, that alleges, in summary, that the Trust and CWAM exposed shareholders of Columbia Acorn International to trading by market timers by allegedly (a) failing to properly evaluate daily whether a significant event affecting the value of the fund's securities had occurred after foreign markets had closed but before the calculation of the fund's net asset value; (b) failing to implement the fund's portfolio valuation and share pricing policies and procedures; and (c) failing to know and implement applicable rules and regulations concerning the calculation of net asset value ("Fair Valuation Lawsuit"). On April 5, 2005, the United States Court of Appeals for the Seventh Circuit ruled that the plaintiffs' state law claims were preempted under federal law resulting in the dismissal of plaintiffs' complaint. Plaintiffs appealed the Seventh Circuit's ruling to the United States Supreme Court. On June 15, 2006, the Supreme Court reversed the Seventh Circuit's ruling on jurisdictional grounds, and the case ultimately was remanded to the state court.

On April 4, 2006, the plaintiffs and the Columbia defendants named in the MDL Action executed an agreement in principle intended to fully resolve all of the lawsuits consolidated in the MDL Action as well as the Fair Valuation Lawsuit. The court entered a stay after the parties executed the agreement in principle. The settlement is subject to court approval.

In 2004, CWAM and the trustees of the Columbia Acorn Trust were named as defendants in certain purported shareholder class and derivative actions making claims, including claims under the Investment Company and the Investment Advisers Acts of 1940 and state law. Certain Columbia Acorn Funds were named as nominal defendants. The suits allege, inter alia, that the fees and expenses paid by the funds are excessive and that the funds' advisers and their affiliates inappropriately used fund assets to distribute the funds and for other improper purposes. On March 2, 2005, the actions were consolidated in the Massachusetts federal court as In re Columbia Entities Litigation. The plaintiffs filed a consolidated amended complaint on June 9, 2005. On November 30, 2005, the judge dismissed all claims by plaintiffs and entered final judgment in favor of the defendants. The plaintiffs appealed to the United States Court of Appeals for the First Circuit on December 30, 2005. A stipulation and settlement agreement dated January 19, 2007 was filed in the First Circuit on February 14, 2007, with a joint stipulation of dismissal and motion for remand to obtain district court approval of the settlement. The joint motion was granted and the appeal was dismissed. On March 6, 2007, the case was remanded to the District Court, where the parties will seek court approval of the settlement. The terms of the proposed settlement, if

30

Managing the Fund

approved, will require payments by the funds' adviser and/or its affiliates, including payment of plaintiffs' attorneys' fees and notice to class members. In the event that the settlement is not approved, the plaintiffs may elect to go forward with their appeal and no opinion is expressed regarding the likely outcome or financial impact of such an appeal on any fund.

On or about January 11, 2005, a putative class action lawsuit was filed in federal district court in Massachusetts against the Trust and its trustees, along with Columbia Management Advisors, LLC, the sub-administrator of the Wanger Advisors Funds and the Columbia Acorn Funds. The plaintiffs allege that the defendants failed to submit Proof of Claims in connection with settlements of securities class action lawsuits filed against companies in which the Columbia Acorn Funds held positions. The complaint seeks compensatory and punitive damages, and the disgorgement of all fees paid to Columbia Management Advisors, LLC. Plaintiffs have voluntarily dismissed the Trust and its independent trustees.

The Trust and CWAM intend to defend these suits vigorously.

As a result of these matters or any adverse publicity or other developments resulting from them, there may be increased redemptions or reduced sales of Fund shares, which could increase transaction costs or operating expenses, or have other adverse consequences for the Fund.

However, based on currently available information, the Trust believes that the likelihood that these lawsuits will have a material adverse impact on any fund is remote, and CWAM believes that the lawsuits are not likely to materially affect its ability to provide investment management services to the Fund.

31

Other Investment Strategies and Risks

Other Investment Strategies and Risks

Thermostat's principal investment strategies and associated risks are described under "The Fund — Principal Investment Strategies" and "The Fund — Principal Investment Risks." This section describes other investments the Portfolio Funds may make and the risks associated with them. In seeking to achieve the investment goals, the Portfolio Funds may invest in various types of securities and engage in various investment techniques that are not their principal focus and therefore are not described in this prospectus. These types of securities and investment practices and their associated risks are identified and discussed in Thermostat's SAI, which you may obtain free of charge (see back cover). The adviser may elect not to buy any of these securities or use any of these techniques. The Fund may not always achieve its investment goal. Except as otherwise noted, approval by Thermostat's shareholders is not required to modif y or change Thermostat's investment strategies.

DERIVATIVE STRATEGIES

The Portfolio Funds may enter into a number of derivative strategies, including those that employ futures, options, straddles on similar investments, to gain or reduce exposure to particular securities or markets. These strategies, commonly referred to as derivatives, involve the use of financial instruments whose values depend on, or are derived from, the value of an underlying security, index or currency. The Portfolio Funds may use these strategies to adjust for both hedging and non-hedging purposes, such as to adjust their sensitivity to changes in interest rates, or to offset a potential loss in one position by establishing an interest in an opposite position. Derivative strategies involve the risk that they may exaggerate a loss, potentially losing more money than the actual cost of the underlying security, or limit a potential gain. Also, with some derivative strategies there is a risk that the other party to the transact ion may fail to honor its contract terms, causing a loss to a Portfolio Fund or that the Portfolio Fund may not be able to find a suitable derivative transaction counterparty, and thus may be unable to invest in derivatives altogether.

WHEN-ISSUED SECURITIES AND FORWARD COMMITMENTS

When-issued securities and forward commitments are securities that are purchased prior to the date they are actually issued or delivered. These securities involve the risk that they may fall in value by the time they are actually issued or that the other party may fail to honor the contract terms.

SHORT SALES

A Portfolio Fund's short sales are subject to special risks. A short sale involves the sale by a Portfolio Fund of a security that it borrows from a third party in the hope of purchasing the same security at a later date at a lower price. In order to deliver the security to the buyer, a Portfolio Fund borrows the security from a third party. The Portfolio Fund is then obligated to return the security to the third party, requiring the Portfolio Fund to purchase the security at the market price at some later date. If the price of the security has increased, then the Portfolio Fund will incur a loss equal to the increase in price of the security from the time that the short sale was entered into, plus any premiums and interest paid to the third party. Therefore, short sales involve the risk that losses may be exaggerated, potentially losing more money than the actual cost of the security at the time it is sold short. Also, < /p>

32

Other Investment Strategies and Risks

there is a risk that the third party to the short sale may fail to honor its contract terms, causing a loss to the Portfolio Fund.

ASSET-BACKED SECURITIES

Asset-backed securities are interests in pools of debt securities backed by various types of loans such as credit card, auto and home equity loans. These securities involve prepayment risk, which is the possibility that the underlying debt may be refinanced or prepaid prior to maturity during periods of declining interest rates. A decline in interest rates may lead to a faster rate of repayment on asset-backed securities and, therefore, cause the Fund to earn a lower rate of return on reinvestment. In addition, the potential impact of prepayment on the price of an asset-backed security may be difficult to predict and result in greater volatility. During periods of rising interest rates, asset-backed securities have a high risk of declining in price because the declining prepayment rates effectively increase the maturity of the securities.

MORTGAGE-BACKED SECURITIES

Mortgage-backed securities are securities that represent ownership interests in large, diversified pools of mortgage loans. Sponsors pool together mortgages of similar rates and terms and offer them as a security to investors.

Most mortgage securities are pooled together and structured as pass-throughs. Monthly payments of principal and interest from the underlying mortgage loans backing the pool are collected by a servicer and "passed through" regularly to the investor. Pass-throughs can have a fixed or an adjustable rate. The majority of pass-through securities are issued by three agencies: Ginnie Mae, Fannie Mae, and Freddie Mac. These securities involve prepayment risk, which is the possibility that the underlying debt may be refinanced or prepaid prior to maturity during periods of declining interest rates. A decline in interest rates may lead to a faster rate of repayment on mortgage-backed securities and, therefore, cause the Fund to earn a lower interest rate on reinvestment. In addition, the potential impact of prepayment on the price of a mortgage-backed security may be difficult to predict and result in greater volatility. During periods of rising interest rates, mortgage-backed securities have a high risk of declining in price because the declining prepayment rates effectively increase the maturity of the securities.

Commercial mortgaged-backed securities are secured by loans to commercial properties such as office buildings, multi-family apartment buildings, and shopping centers. These loans usually contain prepayment penalties that provide protection from refinancing in a declining interest rate environment.

Real estate mortgage investment conduits (REMICs) are multi-class securities that qualify for special tax treatment under the Internal Revenue Code. REMICs invest in certain mortgages that are secured principally by interests in real property such as single family homes.

ZERO COUPON BONDS

Zero coupon bonds do not pay interest in cash on a current basis, but instead accrue interest over the life of the bond. As a result, these securities are issued at a discount. The value of these securities may fluctuate more than the value of similar securities that pay interest periodically. Although these securities pay no interest to holders

33

Other Investment Strategies and Risks

prior to maturity, interest accrued on these securities is reported as income to a Portfolio Fund and distributed to its shareholders.

ILLIQUID INVESTMENTS

A Portfolio Fund may invest up to 15% of its net assets in illiquid investments. An illiquid investment is a security or other position that cannot be disposed of quickly in the normal course of business. For example, some securities are not registered under U.S. securities laws and cannot be sold in public transactions because of Securities and Exchange Commission regulations (these are known as "restricted securities"). Under procedures adopted by a Portfolio's Fund's board of trustees, certain restricted securities may be deemed liquid and will not be counted toward this 15% limit.

TEMPORARY DEFENSIVE STRATEGIES

At times, CWAM or the advisers to the Portfolio Funds may determine that adverse market conditions make it desirable to temporarily suspend the Fund's or Portfolio Funds' respective normal investment activities. During such times, the Fund or Portfolio Funds may, but are not required to, invest in cash or high-quality, short-term debt securities, without limit. Taking a temporary defensive position may prevent the Fund or Portfolio Funds from achieving their respective investment goals.

34

Financial Highlights

The financial highlights table is intended to help you understand the Fund's Class Z financial performance. Information is shown for the Fund's Class Z fiscal years since inception, which run from January 1 to December 31, unless otherwise indicated. Certain information in the table reflects the financial results for a single Class Z share. The total returns in the table represent the return that you would have earned (or lost) on an investment in the Fund (assuming reinvestment of all dividends and distributions). This information has been derived from the Fund's financial statements, which have been audited for the years ended December 31, 2004, 2005 and 2006 by PricewaterhouseCoopers LLP, an independent registered public accounting firm, whose report, along with the Fund's financial statements, is included in the Fund's annual report. The information for the period ended December 31, 2002 and the year ended December 31, 2003 is included in the Fund's financial statements that have been audited by another independent registered public accounting firm, whose report expressed an unqualified opinion on those financial statements and highlights. You can request a free annual report containing those financial statements by calling 1-800-345-6611.

Columbia Thermostat Fund

													Inception September 25, 2002
	Year-ended December 31,												through
	2006			2005			2004			2003			December 31, 2002
	Class Z			Class Z			Class Z			Class Z			Class Z
Net Asset Value — Beginning of Period ($)		12.50			13.12			12.31			10.41			10.00
Income from Investment Operations ($):
Net investment income(a)		0.49			0.43			0.31			0.19			0.04
Net realized and unrealized gain		0.84			0.28			0.82			1.87			0.37
Total from Investment Operations		1.33			0.71			1.13			2.06			0.41
Less Distributions Declared to Shareholders ($):
From net investment income		(0.54	)		(0.42	)		(0.29	)		(0.16	)		—
From net realized gains		(0.72	)		(0.91	)		(0.03	)		(0.00	)(b)		—
Total Distributions Declared to Shareholders		(1.26	)		(1.33	)		(0.32	)		(0.16	)		—
Net Asset Value — End of Period ($)		12.57			12.50			13.12			12.31			10.41
Total return(c)(d) (%)		10.86			5.50			9.17			19.79			4.10	(e)
Ratios to Average Net Assets/Supplemental Data (%):
Expenses(f)		0.25	(g)		0.25	(g)		0.25	(g)		0.38	(g)		0.62	(h)(i)
Net investment income		3.84	(g)		3.28	(g)		2.48	(g)		1.64	(g)		1.41	(h)(i)
Reimbursement/waiver		0.13			0.11			0.21			0.88			19.94	(h)
Portfolio turnover rate (%)		66			96			67			61			11	(e)
Net assets at end of period (in millions) ($)		31			26			21			14			4

(a)  Per share data was calculated using average shares outstanding during the period. Recognition of net investment income by the Fund is affected by the timing of the declaration of dividends by the underlying investment companies in which the Fund invests.

(b)  Rounds to less than $0.01 per share.

(c)  Total return at net asset value assuming all distributions reinvested.

(d)  Had the investment adviser and/or transfer agent not reimbursed a portion of expenses, total return would have been reduced.

(e)  Not annualized.

(f)  Does not include expenses of the investment companies in which the Fund invests.

(g)  The benefits derived from custody fees paid indirectly had no impact.

(h)  Annualized.

(i)  In accordance with a requirement of the Securities and Exchange Commission, the ratios reflect total expenses prior to the reduction of custody fees for cash balances it maintains with the custodian ("custody fees paid indirectly"). The ratios of expenses to average daily net assets and net investment income to average daily net assets net of custody fees paid indirectly would have been 0.60% and 1.43%, respectively, for the period ended December 31, 2002.

35

Appendix A

The following after tax returns of the Portfolio Funds are calculated using the historical highest individual federal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor's tax situation and may differ from those shown, and may not be relevant to investors who hold Portfolio Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

UNDERSTANDING PERFORMANCE

Average annual total returns are a measure of a Portfolio Fund's average performance over the past one-year, five-year and ten-year (or life of Fund) periods. They include the effects of Portfolio Fund expenses.

The Portfolio Fund's returns are compared to an index selected by the Portfolio Funds' adviser. All third-party trademarks are the property of their owners. Unlike each Portfolio Fund, indices are not investments, do not incur fees, expenses or taxes, and are not professionally managed. It is not possible to invest directly in an index.

Average Annual Total Returns — for periods ended December 31, 2006

	Inception Date	1 Year		5 Years		10 Years
Columbia Acorn Fund, Class Z(1) (%)	6/10/70
Return Before Taxes			14.45		14.71		15.16
Return After Taxes on Distributions			12.95		14.07		13.52
Return After Taxes on Distributions and Sale of Fund Shares			11.04		12.85		12.80
Russell 2500® Index (%)	n/a		16.17		12.19		11.26
S&P 500 Index (%)			15.79		6.19		8.42
Russell 2000® Index (%)			18.37		11.39		9.44

(1)  The Fund's Class Z share total net annual fund operating expenses at December 31, 2006 were 0.74%; Class Z and total net assets of the Fund were (in thousands) $12,127,573 and $18,945,126, respectively.

	Inception Date	1 Year		5 Years		Life of the Fund
Columbia Acorn Select, Class Z(1) (%)	11/23/98
Return Before Taxes			19.68		13.67		15.30
Return After Taxes on Distributions			19.11		13.36		14.76
Return After Taxes on Distributions and Sale of Fund Shares			13.21		11.93		13.46
S&P MidCap 400 Index (%)	n/a		10.32		10.89		11.94

(1)  The Fund's Class Z share total net annual fund operating expenses at December 31, 2006 were 0.96%; Class Z and total net assets of the Fund were (in thousands) $909,442 and $2,237,711, respectively.

(2)  Performance information is from November 23, 1998.

36

Appendix A

	Inception Date	1 Year		5 Years		Life of Fund
Columbia Marsico Growth Fund, Class Z(1) (%)	12/31/97
Return Before Taxes			7.18		7.58		8.42
Return After Taxes on Distributions			7.18		7.58		8.37
Return After Taxes on Distributions and Sale of Fund Shares			4.67		6.58		7.42
S&P 500 Index (%)	n/a		15.79		6.19		5.96	(2)

(1)  The Fund's Class Z share total net annual fund operating expenses at March 31, 2006 were 0.96%; Class Z and total net assets of the Fund were (in thousands) $1,446,667 and $4,281,982, respectively.

(2)  Performance information is from December 31, 1997.

	Inception Date	1 Year		5 Years		10 Years(2)
Columbia Acorn International Fund, Class Z(1) (%)	9/22/92
Return Before Taxes			34.53		21.35		13.15
Return After Taxes on Distributions			32.08		20.68		12.01
Return After Taxes on Distributions and Sale of Fund Shares			24.72		18.86		11.26
S&P/Citigroup EMI Global ex-U.S. Index (%)	n/a		30.83		24.39		10.65
MSCI EAFE Index			26.34		14.98		7.71
S&P/Citigroup Global ex-U.S. Cap Range $500M — $5B Index %			26.70		24.15		10.86

(1)  The Fund's Class Z share total net annual fund operating expenses at December 31, 2006 were 0.94%; Class Z and total net assets of the Fund were (in thousands) $3,836,404 and $4,343,395, respectively.

(2)  The Fund's performance in 1999 was achieved during a period of unusual market conditions.

	Inception Date	1 Year		5 Years		Life of Fund
Columbia Dividend Income Fund, Class Z(1) (%)	3/4/98
Return Before Taxes			20.07		7.34		7.97
Return After Taxes on Distributions			19.51		6.97		6.85
Return After Taxes on Distributions and Sale of Fund Shares			13.72		6.24		6.30
Russell 1000 Value Index (%)	n/a		22.25		10.86		8.09	(2)

(1)  The Fund's Class Z share total net annual fund operating expenses at September 30, 2006 were 0.80%; Class Z and total net assets of the Fund were (in thousands) $471,876 and $986,291, respectively.

(2)  Performance information is from March 4, 1998.

	Inception Date	1 Year		5 Years		10 Years
Columbia Large Cap Enhanced Core Fund, Class Z(1) (%)	7/31/96
Return Before Taxes			16.81		6.97		8.46
Return After Taxes on Distributions			14.57		5.29		6.85
Return After Taxes on Distributions and Sale of Fund Shares			11.40		5.06		6.63
S&P 500 Index (%)	n/a		15.79		6.19		8.42	(2)

(1)  The Fund changed its fiscal year end from March 31 to February 28. The Fund's Class Z share total net annual fund operating expenses at March 31, 2006 were 0.50%; Class Z and total net assets of the Fund were (in thousands) $495,099 and $513,618, respectively.

(2)  Performance information is from July 31, 1996.

37

Appendix A

	Inception Date(1)	1 Year		5 Years		10 Years
Columbia Federal Securities Fund, Class Z(2) (%)	1/11/99
Return Before Taxes			3.74		4.40		5.56
Return After Taxes on Distributions			2.04		2.73		3.39
Return After Taxes on Distributions and Sale of Fund Shares			2.40		2.76		3.40
Lehman Brothers Intermediate U.S. Government Bond Index (%)	n/a		3.84		3.92		5.48

(1)  [Class Z is a newer class of shares. Its performance information includes returns of the Fund's Class A shares (the oldest existing fund class) for periods prior to its inception. These returns have not been restated to reflect any differences in expenses (such as Rule 12b-1 fees) between Class A shares and the newer class of shares. The Class A share returns have been adjusted to take into account the fact that Class Z shares are sold without sales charges. If differences in expenses had been reflected, the returns shown for periods prior to the inception of the newer class of shares would have been higher, since Class Z shares are not subject to service fees. Class A shares were initially offered on March 30, 1984, and Class Z shares were initially offered on January 11, 1999.]

(2)  The Fund's Class Z share total net annual fund operating expenses at August 31, 2006 were 0.72%; Class Z and total net assets of the Fund were (in thousands) $109,187 and $848,598, respectively.

	Inception Date	1 Year		5 Years		10 Years
Columbia Intermediate Bond Fund, Class Z(1) (%)	12/5/78
Return Before Taxes			4.60		5.41		6.37
Return After Taxes on Distributions			2.76		3.43		3.97
Return After Taxes on Distributions and Sale of Fund Shares			2.95		3.44		3.95
Lehman Brothers Aggregate Bond Index (%)	n/a		4.33		5.06		6.24

(1)  The Fund's Class Z share total net annual fund operating expenses at March 31, 2006 were 0.64%; Class Z and total net assets of the Fund were (in millions) $1,379 and $1,693, respectively.

	Inception Date	1 Year		5 Years		10 Years
Columbia Conservative High Yield Fund, Class Z(1) (%)	10/1/93
Return Before Taxes			6.17		5.73		6.09
Return After Taxes on Distributions			3.76		3.28		3.13
Return After Taxes on Distributions and Sale of Fund Shares			3.95		3.41		3.34
Merrill Lynch U.S. High Yield, Cash Pay Index (%)	n/a		11.64		9.85		6.86
JP Morgan Developed BB High Yield Index			8.67		8.98		8.14

(1)  The Fund's Class Z share total net annual fund operating expenses at August 31, 2006 were 0.72%; Class Z and total net assets of the Fund were (in millions) $802 and $1,087, respectively.

38

Appendix B

Hypothetical Investment and Expense Information

The Fund is required to disclose the following supplemental hypothetical investment information, which provides additional information about the effect of the expenses paid by the Fund, including investment advisory fees and other Fund costs, on the Fund's returns over a 10-year period. The table shows the estimated expenses that would be charged on a hypothetical investment of $10,000 in Class Z shares of the Fund assuming a 5% return each year, the cumulative return after fees and expenses, and the hypothetical year-end balance after fees and expenses. The table also assumes that all dividends and distributions are reinvested. The annual expense ratio used for the Fund, which is the same as that stated in the Annual Fund Operating Expenses table, is presented in the table, and is net of any contractual fee waivers or expense reimbursements for the period of the contractual commitment. Your actual costs may be higher or lower.< /font>

Columbia Thermostat Fund — Class Z Shares

Maximum Sales Charge 0.00%					Initial Hypothetical Investment Amount $10,000.00						Assumed Rate of Return 5%
Year		Cumulative Return Before Fees & Expenses			Annual Expense Ratio			Cumulative Return After Fees & Expenses			Hypothetical Year-End Balance After Fees & Expenses		Annual Fees & Expenses(1)
	1		5.00	%		0.94	%		4.06	%	$	10,406.00	$	95.91
	2		10.25	%		1.10	%		8.12	%	$	10,811.83	$	116.70
	3		15.76	%		1.10	%		12.33	%	$	11,233.49	$	121.25
	4		21.55	%		1.10	%		16.72	%	$	11,671.59	$	125.98
	5		27.63	%		1.10	%		21.27	%	$	12,126.78	$	130.89
	6		34.01	%		1.10	%		26.00	%	$	12,599.73	$	136.00
	7		40.71	%		1.10	%		30.91	%	$	13,091.11	$	141.30
	8		47.75	%		1.10	%		36.02	%	$	13,601.66	$	146.81
	9		55.13	%		1.10	%		41.32	%	$	14,132.13	$	152.54
	10		62.89	%		1.10	%		46.83	%	$	14,683.28	$	158.49
Total Gain After Fees and Expenses											$	4,683.28
Total Annual Fees and Expenses													$	1,325.87

(1)  Annual Fees and Expenses are calculated based on the average between the beginning and ending balance for each year. All information is calculated on an annual compounding basis.

39

Notes

40

Notes

41

Notes

42

FOR MORE INFORMATION

Additional information about the Fund's investments will be published in the Fund's semiannual and annual reports to shareholders. The annual report will contain a discussion of the market conditions and investment strategies that significantly affected the Fund's performance during its last fiscal year.

You may wish to read the SAI for more information on the Fund and the securities in which it invests. The SAI is incorporated into this prospectus by reference, which means that it is considered to be part of this prospectus.

You can get free copies of annual and semiannual reports and the SAI, request other information and discuss your questions about the Fund by visiting www.columbiafunds.com or by writing or calling the Fund's transfer agent at:

Columbia Management Services, Inc.
P.O. Box 8081
Boston, MA 02266-8081
1-800-345-6611

Text-only versions of all Fund documents can be viewed online or downloaded from the EDGAR database on the Securities and Exchange Commission internet site at www.sec.gov.

You can review and copy information about the Fund, including the SAI, by visiting the following location, and you can obtain copies upon payment of a duplicating fee, by electronic request at the e-mail address publicinfo@sec.gov or by writing the:

Public Reference Room
Securities and Exchange Commission
Washington, DC 20549-0102

Information on the operation of the Public Reference Room may be obtained by calling 1-202-942-8090.

Investment Company Act file number:
Columbia Acorn Trust: 811-01829
•  Columbia Thermostat Fund

©2007 Columbia Management Distributors, Inc.
One Financial Center, Boston, MA 02111-2621
800.426.3750 www.columbiafunds.com

INT-36/130214-0507

COLUMBIA ACORN TRUST

Statement of Additional Information

May 1, 2007

This Statement of Additional Information (“SAI”) contains information that may be useful to investors but is not included in the Prospectuses of Columbia Acorn Trust, formerly named Liberty Acorn Trust (“Columbia Acorn” or “Trust”).  This SAI is not a prospectus and is authorized for distribution only when accompanied or preceded by a Prospectus of the Trust dated May 1, 2007.  This SAI should be read together with a Prospectus and the Trust’s most recent Annual Report dated December 31, 2006.  Investors may obtain a free copy of a Prospectus and Annual Report from Columbia Management Services, Inc. (“CMS”), One Financial Center, Boston, MA 02111-2621, by calling 1-800-345-6611 or by visiting www.columbiafunds.com.  The Financial Statements and Report of the Independent Registered Public Accounting Firm appearing in the Trust’s December 31, 2006 Annual Report are incorporated in this SAI by reference.

Definitions	2
Organization and History	2
Investment Policies	2
Portfolio Turnover	15
Additional Information Concerning Certain Investment Practices	15
Taxes - General	28
Management of the Trust	33
CMD’s Charges and Expenses	51
Legal Proceedings	59
Code of Ethics	59
Anti-Money Laundering Compliance	60
Proxy Voting Policies and Fund Proxy Voting Record	60
Disclosure of Fund Information	60
Custodian	63
Independent Registered Public Accounting Firm	63
Determination of Net Asset Value	63
How to Buy Shares	64
Additional Investor Servicing Payments	65
Additional Financial Intermediary Payments	66
Special Purchase Programs/Investor Services	70
Programs for Reducing or Eliminating Sales Charges	71
How to Sell Shares	74
How to Exchange Shares	76
Distributions	76
Suspension of Redemptions	77
Shareholder Liability	77
Shareholder Meetings	77
Performance Measures and Information	77
Appendix I - Description of Bond Ratings	80
Appendix II — Proxy Voting Policy and Procedures	82

INT-39/130345-0507

1

COLUMBIA ACORN TRUST

Statement of Additional Information

May 1, 2007

DEFINITIONS

“Trust”	Columbia Acorn Trust
“Funds”	Columbia Acorn Fund, Columbia Acorn International, Columbia Acorn USA, Columbia Acorn Select, Columbia Acorn International Select and Columbia Thermostat Fund
“Portfolio Funds”	Funds in which Columbia Thermostat Fund may invest, including Columbia Acorn Fund, Columbia Acorn Select, Columbia Marsico Growth Fund, Columbia Large Cap Enhanced Core Fund, Columbia Acorn International, Columbia Dividend Income Fund, Columbia Federal Securities Fund, Columbia Intermediate Bond Fund and Columbia Conservative High Yield Fund
“Adviser” or “Columbia WAM” or “CWAM”	Columbia Wanger Asset Management, L.P., the Funds’ investment adviser and administrator
“CMD”	Columbia Management Distributors, Inc., the Funds’ distributor
“CMS”	Columbia Management Services, Inc., the Funds’ shareholder services and transfer agent
“CDSC”	Contingent Deferred Sales Charge
“FSF”	Financial Service Firm
“Application”	Investment Account Application
“NAV”	Net Asset Value

ORGANIZATION AND HISTORY

The Trust is a Massachusetts business trust organized on April 21, 1992 as successor to The Acorn Fund, Inc., which became the Acorn Fund series of the Trust.  Prior to October 13, 2003, the Trust was named Liberty Acorn Trust, and prior to September 29, 2000 it was named Acorn Investment Trust.

The Funds are series of the Trust, and each Fund is an open-end, management investment company.  Columbia Acorn Fund, Columbia Acorn International, Columbia Acorn USA, Columbia Acorn International Select and Columbia Thermostat Fund are diversified investment companies and Columbia Acorn Select is a non-diversified investment company.

Each Fund offers four classes of shares – Classes A, B, C and Z shares.  On September 29, 2000, the Funds (other than Columbia Thermostat Fund) changed their names to Liberty Acorn Fund, Liberty Acorn International, Liberty Acorn USA, Liberty Acorn Twenty and Liberty Acorn Foreign Forty.  Effective October 13, 2003, the Funds (except Columbia Thermostat Fund) and the Trust changed their names to their current names.

The Trust is not required to hold annual shareholder meetings, but special meetings may be called for certain purposes.  It is expected that every five years the Trustees will call a meeting of shareholders to elect Trustees.  Shareholders receive one vote for each Fund share.  Shares of each Fund and any other series of the Trust that may be in existence from time to time generally vote together except when required by law to vote separately by Fund or by class.  Shareholders owning in the aggregate 10 percent of Trust shares may call meetings to consider removal of Trustees of the Trust.  Under certain circumstances, the Trust will provide information to assist shareholders in calling such a meeting.

INVESTMENT POLICIES

Columbia Acorn Fund, Columbia Acorn International, Columbia Acorn USA, Columbia Acorn Select and Columbia Acorn International Select invest with the objective of long-term growth of capital, and Columbia Thermostat Fund invests with the objective of long-term total return.  The Funds are designed for investors seeking capital appreciation.  The Funds are not, alone or together, a balanced investment program, and there can be no assurance that any of the Funds will achieve its investment objective.  Columbia Thermostat Fund is a fund of funds that invests in shares of certain portfolios (the “Portfolio Funds”) of Columbia Acorn Trust, Columbia Funds Series Trust and Columbia Funds Series Trust I (the “Underlying Trusts”), all of which are managed by the Adviser or an affiliate of the Adviser.  Columbia Thermostat Fund may invest in the following Portfolio Funds:  Columbia Acorn Fund, Columbia Acorn Select, Columbia Marsico Growth Fund, Columbia Large Cap  

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Enhanced Core Fund, Columbia Acorn International, Columbia Dividend Income Fund, Columbia Federal Securities Fund, Columbia Intermediate Bond Fund and Columbia Conservative High Yield Fund.

Columbia Acorn Fund seeks to invest in growth stocks that are selling at a reasonable price.  Columbia Acorn Fund may invest more in value stocks when the portfolio managers believe value stocks are more attractive and may invest more in growth stocks when the portfolio managers believe growth stocks are more attractive.  On average, Columbia Acorn Fund invests somewhere in between a growth fund and a value fund.

FUNDAMENTAL INVESTMENT POLICIES

The Funds are subject to the following fundamental investment policies, that may not be changed without the affirmative vote of a majority of that Fund’s outstanding voting securities.  The Investment Company Act of 1940 (“1940 Act”) provides that a “vote of a majority of the outstanding voting securities” of a Fund means the affirmative vote of the lesser of (1) more than 50% of the outstanding shares of the Fund, or (2) 67% or more of the shares present at a meeting if more than 50% of the outstanding shares are represented at the meeting in person or by proxy.  The Portfolio Funds in which Columbia Thermostat Fund invests may, but need not, have the same investment policies as Columbia Thermostat Fund.

Columbia Acorn Fund will not:

1.Invest more than 5% of its assets (valued at time of investment) in securities of any one issuer, except in government obligations;

2.Acquire securities of any one issuer which at the time of investment (a) represent more than 10% of the voting securities of the issuer or (b) have a value greater than 10% of the value of the outstanding securities of the issuer;

3.Invest more than 25% of its assets (valued at time of investment) in securities of companies in any one industry;

4.Invest more than 5% of its assets (valued at time of investment) in securities of issuers with less than three years’ operation (including predecessors);

5.Borrow money except (a) from banks for temporary or emergency purposes in amounts not exceeding 33% of the value of the Fund’s assets at the time of borrowing, and (b) in connection with transactions in options and in securities index futures [the Fund will not purchase additional securities when its borrowings, less amounts receivable on sales of portfolio securities, exceed 5% of total assets];

6.Pledge, mortgage or hypothecate its assets, except in connection with permitted borrowings;

7.Underwrite the distribution of securities of other issuers; however, the Fund may acquire “restricted” securities which, in the event of a resale, might be required to be registered under the Securities Act of 1933 on the ground that the Fund could be regarded as an underwriter as defined by that act with respect to such resale; but the Fund will limit its total investment in restricted securities and in other securities for which there is no ready market to not more than 10% of its total assets at the time of acquisition;

8.Purchase and sell real estate or interests in real estate, although it may invest in marketable securities of enterprises which invest in real estate or interests in real estate;

9.Purchase and sell commodities or commodity contracts, except that it may enter into (a) futures and options on futures and (b) forward contracts;

10.Make margin purchases of securities, except for use of such short-term credits as are needed for clearance of transactions and except in connection with transactions in options, futures and options on futures;

11.Sell securities short or maintain a short position, except short sales against-the-box;

12.Participate in a joint or on a joint or several basis in any trading account in securities;

13.Invest in companies for the purpose of management or the exercise of control;

3

14.Issue any senior security except to the extent permitted under the Investment Company Act of 1940;

15.Make loans, but this restriction shall not prevent the Fund from (a) buying a part of an issue of bonds, debentures, or other obligations that are publicly distributed, or from investing up to an aggregate of 15% of its total assets (taken at market value at the time of each purchase) in parts of issues of bonds, debentures or other obligations of a type privately placed with financial institutions, (b) investing in repurchase agreements, or (c) lending portfolio securities, provided that it may not lend securities if, as a result, the aggregate value of all securities loaned would exceed 33% of its total assets (taken at market value at the time of such loan).

Columbia Acorn International will not:

1.With respect to 75% of the value of the Fund’s total assets, invest more than 5% of its total assets (valued at time of investment) in securities of a single issuer, except securities issued or guaranteed by the government of the U.S., or any of its agencies or instrumentalities;

2.Acquire securities of any one issuer that at the time of investment (a) represent more than 10% of the voting securities of the issuer or (b) have a value greater than 10% of the value of the outstanding securities of the issuer;

3.Invest more than 25% of its assets (valued at time of investment) in securities of companies in any one industry;

4.Make loans, but this restriction shall not prevent the Fund from (a) buying a part of an issue of bonds, debentures, or other obligations that are publicly distributed, or from investing up to an aggregate of 15% of its total assets (taken at market value at the time of each purchase) in parts of issues of bonds, debentures or other obligations of a type privately placed with financial institutions, (b) investing in repurchase agreements, or (c) lending portfolio securities, provided that it may not lend securities if, as a result, the aggregate value of all securities loaned would exceed 33% of its total assets (taken at market value at the time of such loan);

5.Borrow money except (a) from banks for temporary or emergency purposes in amounts not exceeding 33% of the value of the Fund’s total assets at the time of borrowing, and (b) in connection with transactions in options, futures and options on futures.  The Fund will not purchase additional securities when its borrowings, less amounts receivable on sales of portfolio securities, exceed 5% of total assets;

6.Underwrite the distribution of securities of other issuers; however the Fund may acquire “restricted” securities which, in the event of a resale, might be required to be registered under the Securities Act of 1933 on the ground that the Fund could be regarded as an underwriter as defined by that act with respect to such resale; but the Fund will limit its total investment in restricted securities and in other securities for which there is no ready market, including repurchase agreements maturing in more than seven days, to not more than 15% of its total assets at the time of acquisition;

7.Purchase and sell real estate or interests in real estate, although it may invest in marketable securities of enterprises that invest in real estate or interests in real estate;

8.Purchase and sell commodities or commodity contracts, except that it may enter into (a) futures and options on futures and (b) forward contracts;

9.Make margin purchases of securities, except for use of such short-term credits as are needed for clearance of transactions and except in connection with transactions in options, futures and options on futures;

10.Sell securities short or maintain a short position, except short sales against-the-box;

11.Issue any senior security except to the extent permitted under the Investment Company Act of 1940.

Columbia Acorn USA will not:

1.With respect to 75% of the value of the Fund’s total assets, invest more than 5% of its total assets (valued at time of investment) in securities of a single issuer, except securities issued or guaranteed by the government of the U.S., or any of its agencies or instrumentalities;

4

2.Acquire securities of any one issuer which at the time of investment (a) represent more than 10% of the voting securities of the issuer or (b) have a value greater than 10% of the value of the outstanding securities of the issuer;

3.Invest more than 25% of its assets (valued at time of investment) in securities of companies in any one industry, except that this restriction does not apply to investments in U.S. government securities;

4.Make loans, but this restriction shall not prevent the Fund from (a) buying a part of an issue of bonds, debentures, or other obligations that are publicly distributed, or from investing up to an aggregate of 15% of its total assets (taken at market value at the time of each purchase) in parts of issues of bonds, debentures or other obligations of a type privately placed with financial institutions, (b) investing in repurchase agreements, or (c) lending portfolio securities, provided that it may not lend securities if, as a result, the aggregate value of all securities loaned would exceed 33% of its total assets (taken at market value at the time of such loan);

5.Borrow money except (a) from banks for temporary or emergency purposes in amounts not exceeding 33% of the value of the Fund’s total assets at the time of borrowing, and (b) in connection with transactions in options, futures and options on futures;

6.Underwrite the distribution of securities of other issuers; however, the Fund may acquire “restricted” securities which, in the event of a resale, might be required to be registered under the Securities Act of 1933 on the ground that the Fund could be regarded as an underwriter as defined by that act with respect to such resale;

7.Purchase and sell real estate or interests in real estate, although it may invest in marketable securities of enterprises which invest in real estate or interests in real estate;

8.Purchase and sell commodities or commodity contracts, except that it may enter into (a) futures and options on futures and (b) foreign currency contracts;

9.Make margin purchases of securities, except for use of such short-term credits as are needed for clearance of transactions and except in connection with transactions in options, futures and options on futures;

10.Issue any senior security except to the extent permitted under the Investment Company Act of 1940.

Neither Columbia Acorn Select nor Columbia Acorn International Select will:

1.With respect to 75% of the value of the Fund’s total assets, invest more than 5% of its total assets (valued at the time of investment) in securities is of a single issuer, except securities issued or guaranteed by the government of the U.S., or any of its agencies or instrumentalities [this restriction applies only to Columbia Acorn International Select];

2.Acquire securities of any one issuer which at the time of investment (a) represent more than 10% of the voting securities of the issuer or (b) have a value greater than 10% of the value of the outstanding securities of the issuer;

3.With respect to 50% of the value of the Fund’s total assets, purchase the securities of any issuer (other than cash items and U.S. government securities and securities of other investment companies) if such purchase would cause the Fund’s holdings of that issuer to exceed 5% of the Fund’s total assets [this restriction applies only to Columbia Acorn Select];

4.Invest more than 25% of its total assets in a single issuer (other than U.S. government securities);

5.Invest more than 25% of its total assets in the securities of companies in a single industry (excluding U.S. government securities);

6.Make loans, but this restriction shall not prevent the Fund from (a) investing in debt securities, (b) investing in repurchase agreements, or (c) lending its portfolio securities, provided that it may not lend securities if, as a result, the aggregate value of all securities loaned would exceed 33% of its total assets (taken at market value at the time of such loan);

7.Borrow money except (a) from banks for temporary or emergency purposes in amounts not exceeding 33% of the value of the Fund’s total assets at the time of borrowing, and (b) in connection with transactions in options, futures and options on futures;

5

8.Underwrite the distribution of securities of other issuers; however, the Fund may acquire “restricted” securities which, in the event of a resale, might be required to be registered under the Securities Act of 1933 on the ground that the Fund could be regarded as an underwriter as defined by that act with respect to such resale;

9.Purchase and sell real estate or interests in real estate, although it may invest in marketable securities of enterprises which invest in real estate or interests in real estate;

10.Purchase and sell commodities or commodity contracts, except that it may enter into (a) futures and options on futures and (b) foreign currency contracts;

11.Make margin purchases of securities, except for use of such short-term credits as are needed for clearance of transactions and except in connection with transactions in options, futures and options on futures;

12.Issue any senior security except to the extent permitted under the Investment Company Act of 1940.

Columbia Thermostat Fund will:

1.Concentrate its investments in shares of other mutual funds.

Columbia Thermostat Fund will not:

1.With respect to 75% of the value of the Fund’s total assets, invest more than 5% of its total assets (valued at time of investment) in securities of a single issuer, except shares of Portfolio Funds and securities issued or guaranteed by the government of the U.S., or any of its agencies or instrumentalities;

2.Make loans, but this restriction shall not prevent the Fund from (a) buying a part of an issue of bonds, debentures, or other obligations that are publicly distributed, or from investing up to an aggregate of 15% of its total assets (taken at market value at the time of each purchase) in parts of issues of bonds, debentures or other obligations of a type privately placed with financial institutions, (b) investing in repurchase agreements, or (c) lending portfolio securities, provided that it may not lend securities if, as a result, the aggregate value of all securities loaned would exceed 33% of its total assets (taken at market value at the time of such loan);

3.Borrow money except (a) from banks for temporary or emergency purposes in amounts not exceeding 33% of the value of the Fund’s total assets at the time of borrowing, and (b) in connection with transactions in options, futures and options on futures;

4.Underwrite the distribution of securities of other issuers; however, the Fund may acquire “restricted” securities which, in the event of a resale, might be required to be registered under the Securities Act of 1933 on the ground that the Fund could be regarded as an underwriter as defined by that act with respect to such resale;

5.Purchase and sell real estate or interests in real estate, although it may invest in marketable securities of enterprises which invest in real estate or interests in real estate;

6.Purchase and sell commodities or commodity contracts, except that it may enter into (a) futures and options on futures and (b) forward contracts;

7.Make margin purchases of securities, except for use of such short-term credits as are needed for clearance of transactions and except in connection with transactions in options, futures and options on futures;

8.Sell securities short or maintain a short position, except short sales against-the-box;

9.Invest in companies for the purpose of management or the exercise of control;

10.Issue any senior security except to the extent permitted under the Investment Company Act of 1940.

6

NON-FUNDAMENTAL INVESTMENT POLICIES

Non-fundamental investment policies may be changed without a shareholder vote.  Each Fund may not:

a.Under normal circumstances, invest less than 65% of its net assets in the securities of foreign companies based in developed markets outside the U.S. [this restriction applies only to Columbia Acorn International Select];

b.Under normal circumstances, invest less than 80% of its net assets (plus any borrowings for investment purposes) in domestic securities [this restriction applies only to Columbia Acorn USA, which will notify shareholders at least 60 days prior to any change in this policy];

c.Acquire securities of other registered investment companies except in compliance with the Investment Company Act of 1940;

d.Invest more than 33% of its total assets (valued at time of investment) in securities of foreign issuers [this restriction applies only to Columbia Acorn Fund];

e.Invest more than 25% of its total (valued at time of investment)  assets in the securities of foreign issuers [this restriction applies only to Columbia Acorn Select];

f.Invest more than 10% of its total assets (valued at the time of investment) in securities of foreign issuers, not including securities represented by American Depository Receipts [this restriction applies only to Columbia Acorn USA];

g.Invest more than 15% of its total assets in domestic securities, under normal market conditions [this restriction applies only to Columbia Acorn International Select];

h.Invest in companies for the purpose of management or the exercise of control;

i.Pledge, mortgage or hypothecate its assets, except as may be necessary in connection with permitted borrowings or in connection with short sales, options, futures and options on futures;

j.Invest more than 10% of its total assets (valued at the time of investment) in restricted securities [this restriction applies only to Columbia Acorn Fund, Columbia Acorn International, Columbia Acorn USA and Columbia Thermostat Fund which will continue to be subject to restriction (k) relating to investments in illiquid securities];

k.Invest more than 15% of its net assets (valued at time of investment) in illiquid securities, including repurchase agreements maturing in more than seven days;

l.Make short sales of securities unless the Fund owns at least an equal amount of such securities, or owns securities that are convertible or exchangeable, without payment of further consideration, into at least an equal amount of such securities; and

m.Acquire securities of other registered open-end investment companies or registered unit investment trusts in reliance on Sections (12)(d)(1)(F) or (G) of the Investment Company Act of 1940 [this restriction applies only to Columbia Acorn Fund, Columbia Acorn International, Columbia Acorn USA and Columbia Acorn Select].

Notwithstanding the foregoing investment restrictions, Columbia Acorn International, Columbia Acorn USA, Columbia Acorn Select and Columbia Acorn International Select may purchase securities pursuant to the exercise of subscription rights, provided that, in the case of Columbia Acorn International, Columbia Acorn USA or Columbia Acorn International Select such purchase will not result in the Fund’s ceasing to be a diversified investment company.  Japanese and European corporations frequently issue additional capital stock by means of subscription rights offerings to existing shareholders at a price substantially below the market price of the shares.  The failure to exercise such rights would result in a Fund’s interest in the issuing company being diluted.  The market for such rights is not well developed in all cases and, accordingly, a Fund may not always realize full value on the sale of rights.  The exception applies in cases where the limits set forth in the investment restrictions would otherwise be exceeded by exercising rights or would have already been exceeded as a result of fluctuations in the market value of Columbia Acorn International’s portfolio securities with the result that the Fund would be forced either to sell securities at a time when it might not otherwise have done so, or to forego exercising its rights.

7

A Fund’s purchase of investment company securities results in the bearing of expenses such that shareholders would indirectly bear a proportionate share of the operating expenses of such investment company, including advisory fees.

Total assets and net assets are determined at current value for purposes of compliance with investment restrictions and policies.  All percentage limitations will apply at the time of investment and are not violated unless an excess or deficiency occurs as a result of such investment.  For the purpose of the 1940 Act’s diversification requirement, an issuer is the entity whose revenues support the security.

INVESTMENT RESTRICTIONS OF PORTFOLIO FUNDS OF COLUMBIA THERMOSTAT FUND

The investment restrictions of each of the Portfolio Funds in which Columbia Thermostat Fund may invest are listed below.

Columbia Acorn Fund - see investment restrictions listed above

Columbia Acorn Select - see investment restrictions listed above

Columbia Marsico Growth Fund (“CMGF”)

Fundamental Investment Policies

1.[The Fund] may not underwrite any issue of securities within the meaning of the 1933 Act except when it might technically be deemed to be an underwriter either: (a) in connection with the disposition of a portfolio security; or (b) in connection with the purchase of securities directly from the issuer thereof in accordance with its investment objective.  This restriction shall not limit the Fund’s ability to invest in securities issued by other registered management investment companies.

2.[The Fund] may not purchase or sell real estate, except that CMGF may purchase securities of issuers which deal or invest in real estate and may purchase securities which are secured by real estate or interests in real estate.

3.[The Fund] may not purchase or sell commodities, except that CMGF may, to the extent consistent with its investment objective, invest in securities of companies that purchase or sell commodities or which invest in such programs, and purchase and sell options, forward contracts, futures contracts, and options on futures contracts. This limitation does not apply to foreign currency transactions, including, without limitation, forward currency contracts.

4.[The Fund] may not purchase any securities which would cause 25% or more of the value of its total assets at the time of purchase to be invested in the securities of one or more issuers conducting their principal business activities in the same industry, provided that: (a) there is no limitation with respect to obligations issued or guaranteed by the U.S. Government, any state or territory of the United States, or any of their agencies, instrumentalities or political subdivisions; and (b) notwithstanding this limitation or any other fundamental investment limitation, assets may be invested in the securities of one or more management investment companies to the extent permitted by the 1940 Act, the rules and regulations thereunder and any exemptive relief obtained by CMGF.

5.[The Fund] may not make loans, except to the extent permitted by the 1940 Act, the rules and regulations thereunder and any exemptive relief obtained by CMGF.

6.[The Fund] may not borrow money or issue senior securities except to the extent permitted by the 1940 Act, the rules and regulations thereunder and any exemptive relief obtained by CMGF.

7.[The Fund] may not purchase securities (except securities issued or guaranteed by the U.S. Government, its agencies or instrumentalities) of any one issuer if, as a result, more than 5% of its total assets will be invested in the securities of such issuer or it would own more than 10% of the voting securities of such issuer, except that: (a) up to 25% of its total assets may be invested without regard to these limitations; and (b) CMGF’s assets may be invested in the securities of one or more management investment companies to the extent permitted by the 1940 Act, the rules and regulations thereunder and any exemptive relief obtained by CMGF.

Non-Fundamental Investment Policies

1.[The Fund] may invest in shares of other open-end management investment companies, subject to the limitations of the 1940 Act, the rules thereunder, and any orders obtained thereunder now or in the future.  If CMGF is purchased by another

8

Fund in reliance on Section 12(d)(1)(G) of the 1940 Act or an exemptive order granting relief from Section 12(d)(1)(G), it will not purchase shares of a registered open-end investment company in reliance on Section 12(d)(1)(F) or Section 12(d)(1)(G) of the 1940 Act. Funds in a master/feeder structure generally invest in the securities of one or more open-end management investment companies pursuant to various provisions of the 1940 Act.

2.[The Fund] may not invest or hold more than 15% of its net assets in illiquid securities. For this purpose, illiquid securities include, among others: (a) securities that are illiquid by virtue of the absence of a readily available market or legal or contractual restrictions on resale; (b) fixed time deposits that are subject to withdrawal penalties and that have maturities of more than seven days; and (c) repurchase agreements not terminable within seven days.

3.[The Fund] may invest in futures or options contracts regulated by the CFTC for: (i) bona fide hedging purposes within the meaning of the rules of the CFTC; and (ii) for other purposes if, as a result, no more than 5% of CMGF’s net assets would be invested in initial margin and premiums (excluding amounts “in-the-money”) required to establish the contracts.

4.[The Fund] may lend securities from its portfolio to brokers, dealers and financial institutions, in amounts not to exceed (in the aggregate) one-third of CMGF’s total assets. Any such loans of portfolio securities will be fully collateralized based on values that are marked to market daily.

5.[The Fund] may not make investments for the purpose of exercising control of management. (Investments by CMGF in entities created under the laws of foreign countries solely to facilitate investment in securities in that country will not be deemed the making of investments for the purpose of exercising control.)

6.[The Fund] may not sell securities short, unless it owns or has the right to obtain securities equivalent in kind and amount to the securities sold short (short sales “against the box”) or CMGF segregates assets in the amount at least equal to the underlying security or asset.

7.To the extent CMGF is subject to Rule 35d-1 under the 1940 Act (the “Names Rule”), and does not otherwise have a fundamental investment policy in place to comply with the Names Rule, it has adopted the following non-fundamental policy:  Shareholders will receive at least 60 days’ notice of any change to CMGF’s investment objective or principal investment strategies made in order to comply with the Names Rule. The notice will be provided in Plain English in a separate written document, and will contain the following prominent statement or similar statement in bold-face type: “Important Notice Regarding Change in Investment Policy.” This statement will appear on both the notice and the envelope in which it is delivered, unless it is delivered separately from other communications to investors, in which case the statement will appear either on the notice or the envelope in which the notice is delivered.

Columbia Large Cap Enhanced Core Fund

Fundamental Investment Policies

1.The Fund may not underwrite any issue of securities within the meaning of the 1933 Act except when it might technically be deemed to be an underwriter either:  (a) in connection with the disposition of a portfolio security; or (b) in connection with the purchase of securities directly from the issuer thereof in accordance with its investment objective.  This restriction shall not limit the Fund’s ability to invest in securities issued by other registered management investment companies.

2.The Fund may not purchase or sell real estate, except the Fund may purchase securities of issuers which deal or invest in real estate and may purchase securities which are secured by real estate or interests in real estate.

3.The Fund may not purchase or sell commodities, except that the Fund may, to the extent consistent with its investment objective, invest in securities of companies that purchase or sell commodities or which invest in such programs, and purchase and sell options, forward contracts, futures contracts, and options on futures contracts.  This limitation does not apply to foreign currency transactions, including, without limitation, forward currency contracts.

4.The Fund may not purchase any securities which would cause 25% or more of the value of its total assets at the time of purchase to be invested in the securities of one or more issuers conducting their principal business activities in the same industry, provided that: (a) there is no limitation with respect to obligations issued or guaranteed by the U.S. Government, any state or territory of the United States, or any of their agencies, instrumentalities or political subdivisions; and (b) notwithstanding this limitation or any other fundamental investment limitation, assets may be invested in the securities of

9

one or more management investment companies to the extent permitted by the 1940 Act, the rules and regulations thereunder and any exemptive relief obtained by the Fund.

5.The Fund may not make loans, except to the extent permitted by the 1940 Act, the rules and regulations thereunder and any exemptive relief obtained by the Fund.

6.The Fund may not borrow money or issue senior securities except to the extent permitted by the 1940 Act, the rules and regulations thereunder and any exemptive relief obtained by the Fund.

7.The Fund may not purchase securities (except securities issued or guaranteed by the U.S. Government, its agencies or instrumentalities) of any one issuer if, as a result, more than 5% of its total assets will be invested in the securities of such issuer or it would own more than 10% of the voting securities of such issuer, except that:  (a) up to 25% of its total assets may be invested without regard to these limitations; and (b) the Fund’s assets may be invested in the securities of one or more management investment companies to the extent permitted by the 1940 Act, the rules and regulations thereunder and any exemptive relief obtained by the Fund.

Non-Fundamental Investment Policies

1.The Fund may invest in shares of other open-end management investment companies, subject to the limitations of the 1940 Act, the rules thereunder, and any orders obtained thereunder now or in the future.  Any Fund that is purchased by another Fund in reliance on Section 12(d)(1)(G) of the 1940 Act or an exemptive order granting relief from Section 12(d)(1)(G) will not purchase shares of a registered open-end investment company in reliance on Section 12(d)(1)(F) or Section 12(d)(1)(G) of the 1940 Act.  Funds in a master/feeder structure generally invest in the securities of one or more open-end management investment companies pursuant to various provisions of the 1940 Act.

2.The Fund may not invest or hold more than 15% of the Fund’s net assets in illiquid securities.  For this purpose, illiquid securities include, among others: (a) securities that are illiquid by virtue of the absence of a readily available market or legal or contractual restrictions on resale; (b) fixed time deposits that are subject to withdrawal penalties and that have maturities of more than seven days; and (c) repurchase agreements not terminable within seven days.

3.The Fund may invest in futures or options contracts regulated by the CFTC for:  (i) bona fide hedging purposes within the meaning of the rules of the CFTC; and (ii) for other purposes if, as a result, no more than 5% of the Fund’s net assets would be invested in initial margin and premiums (excluding amounts “in-the-money”) required to establish the contracts.

4.The Fund may lend securities from its portfolio to brokers, dealers and financial institutions, in amounts not to exceed (in the aggregate) one-third of the Fund’s total assets.  Any such loans of portfolio securities will be fully collateralized based on values that are marked to market daily.

5.The Fund may not make investments for the purpose of exercising control of management.  (Investments by the Fund in entities created under the laws of foreign countries solely to facilitate investment in securities in that country will not be deemed the making of investments for the purpose of exercising control.)

6.The Fund may not sell securities short, unless it owns or has the right to obtain securities equivalent in kind and amount to the securities sold short (short sales “against the box”) or the Fund segregates assets in the amount at least equal to the underlying security or asset.

7.To the extent the Fund is subject to Rule 35d-1 under the 1940 Act (the “Names Rule”), and does not otherwise have a fundamental investment policy in place to comply with the Names Rule, it has adopted the following non-fundamental policy:  Shareholders will receive at least 60 days’ notice of any change to a Fund’s investment objective or principal investment strategies made in order to comply with the Names Rule.  The notice will be provided in Plain English in a separate written document, and will contain the following prominent statement or similar statement in bold-face type:  “Important Notice Regarding Change in Investment Policy.”  This statement will appear on both the notice and the envelope in which it is delivered, unless it is delivered separately from other communications to investors, in which case the statement will appear either on the notice or the envelope in which the notice is delivered.

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Columbia Acorn International – see investment restrictions listed herein

Columbia Dividend Income Fund

Fundamental Investment Policies

The Fund may not, as a matter of fundamental policy:

1.Underwrite any issue of securities issued by other persons within the meaning of the Securities Act of 1933, as amended (the “1933 Act”) except when it might be deemed to be an underwriter either:  (a) in connection with the disposition of a portfolio security; or (b) in connection with the purchase of securities directly from the issuer thereof in accordance with its investment objective.  This restriction shall not limit the Fund’s ability to invest in securities issued by other registered investment companies.

2.Purchase or sell real estate, except the Fund may purchase securities of issuers which deal or invest in real estate and may purchase securities which are secured by real estate or interests in real estate and it may hold and dispose of real estate or interests in real estate acquired through the exercise of its rights as a holder of securities which are secured by real estate or interests therein.

3.Purchase or sell commodities, except that the Fund may to the extent consistent with its investment objective, invest in securities of companies that purchase or sell commodities or which invest in such programs, and purchase and sell options, forward contracts, futures contracts, and options on futures contracts and enter into swap contracts and other financial transactions relating to commodities.  This limitation does not apply to foreign currency transactions including without limitation forward currency contracts.

4.Purchase any securities which would cause 25% or more of the value of its total assets at the time of purchase to be invested in the securities of one or more issuers conducting their principal business activities in the same industry, provided that:  (a) there is no limitation with respect to obligations issued or guaranteed by the U.S. Government, any state or territory of the United States, or any of their agencies, instrumentalities or political subdivisions; and (b) notwithstanding this limitation or any other fundamental investment limitation, assets may be invested in the securities of one or more management investment companies to the extent permitted by the 1940 Act, the rules and regulations thereunder and any applicable exemptive relief.

5.Make loans, except to the extent permitted by the 1940 Act, the rules and regulations thereunder and any applicable exemptive relief.

6.Borrow money or issue senior securities except to the extent permitted by the 1940 Act, the rules and regulations thereunder and any applicable exemptive relief.

7.Purchase securities (except securities issued or guaranteed by the U.S. Government, its agencies or instrumentalities) of any one issuer if, as a result, more than 5% of its total assets will be invested in the securities of such issuer or it would own more than 10% of the voting securities of such issuer, except that:  (a) up to 25% of its total assets may be invested without regard to these limitations and (b) the Fund’s assets may be invested in the securities of one or more management investment companies to the extent permitted by the 1940 Act, the rules and regulations thereunder, or any applicable exemptive relief.

Non-Fundamental Investment Policies

The following investment limitation with respect to the Fund may be changed by the Board of Trustees without shareholder approval:

1.The Fund may not sell securities short, maintain a short position, or purchase securities on margin, except for such short-term credits as are necessary for the clearance of transactions.

2.The Fund may not write or sell put options, call options, straddles, spreads or any combination thereof except that it may buy and sell options, including without limit buying or writing puts and calls, based on any type of security, index or currency, including options on foreign exchanges and options not traded on exchanges to the extent permitted by its investment objective and policies.

3.The Fund may not purchase securities of companies for the purpose of exercising control.

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4.The Fund may not acquire securities of other registered open-end investment companies or registered unit investment trusts in reliance on Sections 12(d)(1)(F) or (G) of the Investment Company Act of 1940.

5.The Fund may not invest more than 15% of its net assets in illiquid securities.

Columbia Federal Securities Fund

Fundamental Investment Policies

Columbia Federal Securities Fund may not:

1.Underwrite any issue of securities issued by other persons within the meaning of the Securities Act of 1933 (the “1933 Act”) except when it might be deemed to be an underwriter either:  (a) in connection with the disposition of a portfolio security; or (b) in connection with the purchase of securities directly from the issuer thereof in accordance with its investment objective.  This restriction shall not limit the Fund’s ability to invest in securities issued by other registered investment companies;

2.Purchase or sell real estate, except the Fund may purchase securities of issuers which deal or invest in real estate and may purchase securities which are secured by real estate or interests in real estate and it may hold and dispose of real estate or interests in real estate acquired through the exercise of its rights as a holder of securities which are secured by real estate or interests therein;

3.Purchase or sell commodities, except that the Fund may to the extent consistent with its investment objective, invest in securities of companies that purchase or sell commodities or which invest in such programs, and purchase and sell options, forward contracts, futures contracts, and options on futures contracts and enter into swap contracts and other financial transactions relating to commodities.  This limitation does not apply to foreign currency transactions including without limitation forward currency contracts.

4.Purchase any securities which would cause 25% or more of the value of its total assets at the time of purchase to be invested in the securities of one or more issuers conducting their principal business activities in the same industry, provided that:  (a) there is no limitation with respect to obligations issued or guaranteed by the U.S. Government, any state or territory of the United States, or any of their agencies, instrumentalities or political subdivisions; and (b) notwithstanding this limitation or any other fundamental investment limitation, assets may be invested in the securities of one or more management investment companies to the extent permitted by the 1940 Act, the rules and regulations thereunder and any applicable exemptive relief;

5.Make loans, except to the extent permitted by the 1940 Act, the rules and regulations thereunder and any applicable exemptive relief;

6.Borrow money or issue senior securities except to the extent permitted by the 1940 Act, the rules and regulations thereunder and any applicable exemptive relief; and

7.Purchase securities (except securities issued or guaranteed by the U.S. Government, its agencies or instrumentalities) of any one issuer if, as a result, more than 5% of its total assets will be invested in the securities of such issuer or it would own more than 10% of the voting securities of such issuer, except that:  (a) up to 25% of its total assets may be invested without regard to these limitations and (b) a Fund’s assets may be invested in the securities of one or more management investment companies to the extent permitted by the 1940 Act, the rules and regulations thereunder, or any applicable exemptive relief.

Non-Fundamental Investment Policies

Columbia Federal Securities Fund may not:

1.Purchase securities on margin, but it may receive short-term credit to clear securities transactions and may make initial or maintenance margin deposits in connection with futures transactions; and

2.Invest more than 15% of its net assets in illiquid assets.

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3.Acquire securities of other registered open-end investment companies or registered unit investment trusts in reliance on section 12(d)(1)(F) or (G) of the Investment Company Act of 1940.

Columbia Intermediate Bond Fund

Fundamental Investment Policies

Columbia Intermediate Bond Fund may not:

1.Underwrite any issue of securities issued by other persons within the meaning of the 1933 Act except when it might be deemed to be an underwriter either:  (a) in connection with the disposition of a portfolio security; or (b) in connection with the purchase of securities directly from the issuer thereof in accordance with its investment objective.  This restriction shall not limit the Portfolio’s ability to invest in securities issued by other registered investment companies;

2.Purchase or sell real estate, except a Fund may purchase securities of issuers which deal or invest in real estate and may purchase securities which are secured by real estate or interests in real estate and it may hold and dispose of real estate or interests in real estate acquired through the exercise of its rights as a holder of securities which are secured by real estate or interests therein;

3.Purchase or sell commodities, except that the Fund may to the extent consistent with its investment objective, invest in securities of companies that purchase or sell commodities or which invest in such programs, and purchase and sell options, forward contracts, futures contracts, and options on futures contracts and enter into swap contracts and other financial transactions relating to commodities.  This limitation does not apply to foreign currency transactions including without limitation forward currency contracts.

4.Purchase any securities which would cause 25% or more of the value of its total assets at the time of purchase to be invested in the securities of one or more issuers conducting their principal business activities in the same industry, provided that:  (a) there is no limitation with respect to obligations issued or guaranteed by the U.S. Government, any state or territory of the United States, or any of their agencies, instrumentalities or political subdivisions; and (b) notwithstanding this limitation or any other fundamental investment limitation, assets may be invested in the securities of one or more management investment companies to the extent permitted by the 1940 Act, the rules and regulations thereunder and any applicable exemptive relief;

5.Make loans, except to the extent permitted by the 1940 Act, the rules and regulations thereunder and any applicable exemptive relief;

6.Borrow money or issue senior securities except to the extent permitted by the 1940 Act, the rules and regulations thereunder and any applicable exemptive relief; and

7.Purchase securities (except securities issued or guaranteed by the U.S. Government, its agencies or instrumentalities) of any one issuer if, as a result, more than 5% of its total assets will be invested in the securities of such issuer or it would own more than 10% of the voting securities of such issuer, except that:  (a) up to 25% of its total assets may be invested without regard to these limitations and (b) a Fund’s assets may be invested in the securities of one or more management investment companies to the extent permitted by the 1940 Act, the rules and regulations thereunder, or any applicable exemptive relief.

Non-Fundamental Investment Policies

Columbia Intermediate Bond Fund may not:

(A)Invest for the purpose of exercising control or management;

(B)Purchase more than 3% of the stock of another investment company or purchase stock of other investment companies equal to more than 5% of its total assets (valued at time of purchase) in the case of any one other investment company and 10% of such assets (valued at time of purchase) in the case of all other investment companies in the aggregate; any such purchases are to be made in the open market where no profit to a sponsor or dealer results from the purchase, other than the customary broker’s commission, except for securities acquired as part of a merger, consolidation or acquisition of assets; (1)

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(C)Purchase portfolio securities from, or sell portfolio securities to, any of the officers and directors or trustees of the Trust or of its investment adviser;

(D)Purchase shares of other open-end investment companies, except in connection with a merger, consolidation, acquisition, or reorganization;

(E)Invest more than 5% of its net assets (valued at time of investment) in warrants, no more than 2% of its net assets in warrants which are not listed on the New York or American Stock Exchange;

(F)Purchase a put or call option if the aggregate premiums paid for all put and call options exceed 20% of its net assets (less the amount by which any such positions are in-the-money), excluding put and call options purchased as closing transactions;

(G)Write an option on a security unless the option is issued by the Options Clearing Corporation, an exchange, or similar entity;

(H)Invest in limited partnerships in real estate unless they are readily marketable;

(I)Sell securities short unless (i) it owns or has the right to obtain securities equivalent in kind and amount to those sold short at no added cost or (ii) the securities sold are “when issued” or “when distributed” securities which it expects to receive in a recapitalization, reorganization, or other exchange for securities it contemporaneously owns or has the right to obtain and provided that transactions in options, futures, and options on futures are not treated as short sales;

(J)Invest more than 15% of its total assets (taken at market value at the time of a particular investment) in restricted securities, other than securities eligible for resale pursuant to Rule 144A under the Securities Act of 1933;

(K)Invest more than 15% of its net assets (taken at market value at the time of a particular investment) in illiquid securities, including repurchase agreements maturing in more than seven days;

(L)Purchase securities on margin, except for use of short-term credit necessary for clearance of purchases and sales of portfolio securities, but it may make margin deposits in connection with transactions in options, futures, and options on futures.

(1)The Fund has been informed that the staff of the Securities and Exchange commission takes the position that the issuers of certain collateralized mortgage obligations and certain other collateralized assets are investment companies and that subsidiaries of foreign banks may be investment companies for purposes of Section 12(d)(1) of the 1940 Act, which limits the ability of one investment company to invest in another investment company.  Accordingly, the Fund intends to operate within the applicable limitations under Section 12(d)(1)(A) of the 1940 Act.

Columbia Conservative High Yield Fund

Fundamental Investment Policies

Columbia Conservative High Yield Fund may not:

1.Underwrite any issue of securities issued by other persons within the meaning of the Securities Act of 1933, as amended (“1933 Act”) except when it might be deemed to be an underwriter either:  (a) in connection with the disposition of a portfolio security; or (b) in connection with the purchase of securities directly from the issuer thereof in accordance with its investment objective.  This restriction shall not limit the Portfolio’s ability to invest in securities issued by other registered investment companies;

2.Purchase or sell real estate, except a Fund may purchase securities of issuers which deal or invest in real estate and may purchase securities which are secured by real estate or interests in real estate and it may hold and dispose of real estate or interests in real estate acquired through the exercise of its rights as a holder of securities which are secured by real estate or interests therein;

3.Purchase or sell commodities, except that the Fund may to the extent consistent with its investment objective, invest in securities of companies that purchase or sell commodities or which invest in such programs, and purchase and sell options, forward contracts, futures contracts, and options on futures contracts and enter into swap contracts and other financial

14

transactions relating to commodities.  This limitation does not apply to foreign currency transactions including without limitation forward currency contracts.

4.With the exception of the Real Estate Fund, which will invest at least 65% of the value of its total assets in securities of companies principally engaged in the real estate industry, purchase any securities which would cause 25% or more of the value of its total assets at the time of purchase to be invested in the securities or one or more issuers conducting their principal business activities in the same industry, provided that:  (a) there is no limitation with respect to obligations issued or guaranteed by the U.S. Government, any state or territory of the United States, or any of their agencies, instrumentalities or political subdivisions; and (b) notwithstanding this limitation or any other fundamental investment limitation, assets may be invested in the securities of one or more management investment companies to the extent permitted by the 1940 Act, the rules and regulations thereunder and any applicable exemptive relief.

5.Make loans, except to the extent permitted by the 1940 Act, the rules and regulations thereunder and any applicable exemptive relief.

6.Borrow money or issue senior securities except to the extent permitted by the 1940 Act, the rules and regulations thereunder and any applicable exemptive relief.

7.With the exception of the Oregon Intermediate Municipal Bond Fund and the Technology Fund, purchase securities (except securities issued or guaranteed by the U.S. Government, its agencies or instrumentalities) of any one issuer if, as a result, more than 5% of its total assets will be invested in the securities of such issuer or it would own more than 10% of the voting securities of such issuer, except that;  (a) up to 25% of its total assets may be invested without regard to these limitations and (b) a Fund’s assets may be invested in the securities of one or more management investment companies to the extent permitted by the 1940 Act, the rules and regulations thereunder, or any applicable exemptive relief.

Non-Fundamental Investment Policies

Columbia Conservative High Yield Fund may not:

1.Purchase or otherwise acquire any security if, as a result, more than 15% of its net assets would be invested in securities that are illiquid.

PORTFOLIO TURNOVER

Portfolio turnover information is included in the Prospectuses under “Financial Highlights.”  High portfolio turnover in a Fund’s portfolio may cause a Fund to realize capital gains which, if realized and distributed by the Fund, may be taxable to shareholders as ordinary income.  High portfolio turnover in a Fund’s portfolio may also result in correspondingly greater brokerage commissions and other transaction costs, which will be borne directly by the Fund.  Under normal conditions, the portfolio turnover rates of Columbia Acorn Fund and Columbia Acorn USA are expected to be below about 50%, and of Columbia Acorn International, Columbia Acorn International Select and Columbia Acorn Select are likely to be below 75%, 125% and 75%, respectively.  Although under normal market conditions the portfolio turnover rate of Columbia Thermostat Fund is expected to be below 100%, it could exceed 100%.

ADDITIONAL INFORMATION CONCERNING CERTAIN INVESTMENT PRACTICES

In this section the term “Fund” refers to a Fund or a Portfolio Fund except where otherwise indicated.  Additional information concerning certain of the Funds’ investments and investment practices is set forth below.

Common Stocks

Columbia Acorn Fund, Columbia Acorn International, Columbia Acorn USA, Columbia Acorn Select and Columbia Acorn International Select will invest mostly in common stocks, which represent an equity interest (ownership) in a corporation.  Columbia Thermostat Fund invests in shares of Portfolio Funds, some of which invest in common stocks.  This ownership interest often gives a Fund or Portfolio Fund the right to vote on measures affecting a company’s organization and operations.  The Funds and some Portfolio Funds also invest in other types of equity securities, including preferred stocks and securities convertible into common stocks.  Some of the Portfolio Funds also invest in fixed-income securities.  Over time, common stocks have historically provided superior long-term capital growth potential.  However, stock prices may decline over short or even

15

extended periods.  Stock markets tend to move in cycles, with periods of rising stock prices and periods of falling stock prices.  As a result, the Funds should be considered long-term investments, designed to provide the best results when held for several years or more.  The Funds may not be suitable investments if you have a short-term investment horizon or are unwilling to accept fluctuations in share price, including significant declines over a given period.  Under normal conditions, the common stock investments of the Funds other than Columbia Thermostat Fund (as a percent of total assets) are allocated as follows:

	U.S. Companies	Foreign Companies
Fund	Maximum	Maximum
Columbia Acorn Fund	no limit	up to 33%
Columbia Acorn International	up to 25%	no limit
Columbia Acorn USA	no limit	up to 10%
Columbia Acorn Select	no limit	up to 25%
Columbia Acorn International Select	up to 15%	no limit

See also the discussion of foreign securities below.  Columbia Thermostat Fund invests in Portfolio Funds that may have their own geographic limits.

Diversification

Diversification is a means of reducing risk by investing in a broad range of stocks or other securities.  Because Columbia Acorn Select is non-diversified, it has the ability to take larger positions in a smaller number of issuers.  The appreciation or depreciation of a single stock may have a greater impact on the NAV of a non-diversified fund, because it is likely to have a greater percentage of its assets invested in that stock.  As a result, the share price of Columbia Acorn Select can be expected to fluctuate more than that of broadly diversified funds investing in similar securities.  Because it is non-diversified, Columbia Acorn Select is not subject to the limitations under the 1940 Act in the percentage of its assets that it may invest in any one issuer.  The Fund, however, intends to comply with the diversification standards for regulated investment companies under Subchapter M of the Internal Revenue Code (summarized above under “Investment Policies”).

Foreign Securities

The Funds and some Portfolio Funds invest in securities traded in markets outside the United States.  Foreign investments can be affected favorably or unfavorably by changes in currency rates and in exchange control regulations.  There may be less publicly available information about a foreign company than about a U.S. company, and foreign companies may not be subject to accounting, auditing and financial reporting standards comparable to those applicable to U.S. companies.  Securities of some foreign companies are less liquid or more volatile than securities of U.S. companies, and foreign brokerage commissions and custodian fees may be higher than in the United States.  Investments in foreign securities can involve other risks different from those affecting U.S. investments, including currency fluctuation, local political or economic developments, expropriation or nationalization of assets and imposition of withholding taxes on dividend or interest payments.  Foreign securities, like other assets of the Funds, will be held by the Funds’ custodian or by a sub-custodian or depository.

As noted above, under normal market conditions, each Fund may invest in foreign securities (as a percentage of total assets).

Columbia Acorn International Select invests primarily in developed countries but may invest up to 15% of its total assets in “emerging markets or frontier markets.”  The Funds use the terms “developed markets” and “emerging markets” as those terms are defined by the International Financial Corporation, a member of the World Bank Group.

Columbia Thermostat Fund invests in Portfolio Funds that may have their own geographic limits.

The Funds and some Portfolio Funds may invest in securities of foreign issuers directly or in the form of American Depositary Receipts (“ADRs”), European Depositary Receipts (“EDRs”), Global Depositary Receipts (“GDRs”) or other securities representing underlying shares of foreign issuers.  Positions in these securities are not necessarily denominated in the same currency as the common stocks into which they may be converted.  ADRs are receipts typically issued by an American bank or trust company evidencing ownership of the underlying securities.  EDRs are European receipts evidencing a similar arrangement.  GDRs trade in both domestic and foreign markets.  Generally ADRs, in registered form, are designed for use in the U.S. securities markets, and EDRs, in bearer form, are designed for use in European securities markets.  The Funds and some Portfolio Funds may invest in both “sponsored” and “unsponsored” depositary receipts.  In a sponsored depositary receipt, the issuer typically pays some or all of the expenses of the depository and agrees to provide its regular shareholder

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communications to depositary receipt holders.  An unsponsored depositary receipt is created independently of the issuer of the underlying security, and the receipt holders generally pay the expenses of the depository and do not have an undertaking from the issuer of the underlying security to furnish shareholder communications.  Therefore, in the case of an unsponsored depositary receipt, a Fund is likely to bear its proportionate share of the expenses of the depository and it may have greater difficulty in receiving shareholder communications than it would have with a sponsored depositary receipt.  None of the Columbia Acorn Funds expects to invest 5% or more of its total assets in unsponsored depositary receipts.

The investment performance of a Fund that invests in securities of foreign issuers is affected by the strength or weakness of the U.S. dollar against the currencies of the foreign markets in which its securities trade or in which they are denominated.  For example, if the dollar falls in value relative to the Japanese yen, the dollar value of a yen-denominated stock held in the portfolio will rise even though the price of the stock remains unchanged.  Conversely, if the dollar rises in value relative to the yen, the dollar value of the yen-denominated stock will fall.  (See discussion of transaction hedging and portfolio hedging under “Currency Exchange Transactions.”)

Currency Exchange Transactions

The Funds and some Portfolio Funds may enter into currency exchange transactions.  A currency exchange transaction may be conducted either on a spot (i.e., cash) basis at the spot rate for purchasing or selling currency prevailing in the foreign exchange market or through a forward currency exchange contract (“forward contract”).  A forward contract is an agreement to purchase or sell a specified currency at a specified future date (or within a specified time period) and price set at the time of the contract.  Forward contracts are usually entered into with banks, foreign exchange dealers or broker-dealers, are not exchange-traded, and are usually for less than one year, but may be renewed.

Forward currency transactions may involve currencies of the different countries in which a Fund may invest and serve as hedges against possible variations in the exchange rate between these currencies.  The Funds’ currency transactions are limited to transaction hedging and portfolio hedging involving either specific transactions or portfolio positions, except to the extent described below under “Synthetic Foreign Money Market Positions.”  Transaction hedging is the purchase or sale of a forward contract with respect to specific payables or receivables of a fund accruing in connection with the purchase or sale of portfolio securities.  Portfolio hedging is the use of a forward contract with respect to a portfolio security position denominated or quoted in a particular currency.  A Fund may engage in portfolio hedging with respect to the currency of a particular country in amounts approximating actual or anticipated positions in securities denominated in that currency.  When a Fund owns or anticipates owning securities in countries whose currencies are linked, the Adviser may aggregate such positions as to the currency hedged.

If a Fund enters into a forward contract hedging an anticipated purchase of portfolio securities, assets of that Fund having a value at least as great as the Fund’s commitment under such forward contract will be segregated on the books of the Fund while the contract is outstanding.

At the maturity of a forward contract to deliver a particular currency, a Fund may either sell the portfolio security related to the contract and make delivery of the currency, or it may retain the security and either acquire the currency on the spot market or terminate its contractual obligation to deliver the currency by purchasing an offsetting contract with the same currency trader obligating it to purchase on the same maturity date the same amount of the currency.

It is impossible to forecast with absolute precision the market value of portfolio securities at the expiration of a forward contract.  Accordingly, it may be necessary for a Fund to purchase additional currency on the spot market (and bear the expense of such purchase) if the market value of the security is less than the amount of currency that the Fund is obligated to deliver and if a decision is made to sell the security and make delivery of the currency.  Conversely, it may be necessary to sell on the spot market some of the currency received upon the sale of the portfolio security if its market value exceeds the amount of currency that Fund is obligated to deliver.

If a Fund retains the portfolio security and engages in an offsetting transaction, the Fund will incur a gain or a loss to the extent that there has been movement in forward contract prices.  If the Fund engages in an offsetting transaction, it may subsequently enter into a new forward contract to sell the currency.  Should forward prices decline during the period between a Fund’s entering into a forward contract for the sale of a currency and the date it enters into an offsetting contract for the purchase of the currency, the Fund will realize a gain to the extent the price of the currency it has agreed to sell exceeds the price of the currency it has agreed to purchase.  Should forward prices increase, a Fund will suffer a loss to the extent the price of the currency it has agreed to purchase exceeds the price of the currency it has agreed to sell.  A default on the contract would deprive the Fund of unrealized profits or force the Fund to cover its commitments for purchase or sale of currency, if any, at the current market price.

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Hedging against a decline in the value of a currency does not eliminate fluctuations in the prices of portfolio securities or prevent losses if the prices of such securities decline.  Such transactions also preclude the opportunity for gain if the value of the hedged currency should rise.  Moreover, it may not be possible for a Fund to hedge against a devaluation that is so generally anticipated that the Fund is not able to contract to sell the currency at a price above the devaluation level it anticipates.  The cost to a Fund of engaging in currency exchange transactions varies with such factors as the currency involved, the length of the contract period, and prevailing market conditions.  Since currency exchange transactions are usually conducted on a principal basis, no fees or commissions are involved.

Synthetic Foreign Money Market Positions.  The Funds may invest in money market instruments denominated in foreign currencies.  In addition to, or in lieu of, such direct investment, the Funds may construct a synthetic foreign money market position by (a) purchasing a money market instrument denominated in one currency (generally U.S. dollars) and (b) concurrently entering into a forward contract to deliver a corresponding amount of that currency in exchange for a different currency on a future date and at a specified rate of exchange.  For example, a synthetic money market position in Japanese yen could be constructed by purchasing a U.S. dollar money market instrument, and entering concurrently into a forward contract to deliver a corresponding amount of U.S. dollars in exchange for Japanese yen on a specified date and at a specified rate of exchange.  Because of the availability of a variety of highly liquid short-term U.S. dollar money market instruments, a synthetic money market position utilizing such U.S. dollar instruments may offer greater liquidity than direct investment in foreign money market instruments.  The results of a direct investment in a foreign currency and a concurrent construction of a synthetic position in such foreign currency, in terms of both income yield and gain or loss from changes in currency exchange rates, in general should be similar, but would not be identical because the components of the alternative investments would not be identical.  Except to the extent a synthetic foreign money market position consists of a money market instrument denominated in a foreign currency, the synthetic foreign money market position shall not be deemed a “foreign security” for purposes of the Funds’ investment limits.

OTC Derivatives.  The Funds may buy and sell over-the-counter (“OTC”) derivatives.  Unlike exchange-traded derivatives, which are standardized with respect to the underlying instrument, expiration date, contract size, and strike price, the terms of OTC derivatives (derivatives not traded on exchanges) generally are established through negotiation with the other party to the contract.  Although this type of arrangement allows a Fund greater flexibility to tailor an instrument to its needs, OTC derivatives generally involve greater credit risk than exchange-traded derivatives, which are guaranteed by the clearing organization of the exchanges where they are traded.  Each Fund (not including the Portfolio Funds) will limit its investments so that no more than 5% of its total assets will be placed at risk in the use of OTC derivatives.  See “Illiquid and Restricted Securities” below for more information on the risks associated with investing in OTC derivatives.

Risks Associated with Options.  There are several risks associated with transactions in options.  For example, there are significant differences between the securities markets, the currency markets, and the options markets that could result in an imperfect correlation between these markets, causing a given transaction not to achieve its objectives.  A decision as to whether, when, and how to use options involves the exercise of skill and judgment, and even a well-conceived transaction may be unsuccessful to some degree because of market behavior or unexpected events.

There can be no assurance that a liquid market will exist when a Fund seeks to close out an option position.  If a Fund were unable to close out an option that it had purchased on a security, it would have to exercise the option in order to realize any profit or the option would expire and become worthless.  If a Fund were unable to close out a covered call option that it had written on a security, it would not be able to sell the underlying security until the option expired.  As the writer of a covered call option on a security, a Fund foregoes, during the option’s life, the opportunity to profit from increases in the market value of the security covering the call option above the sum of the premium and the exercise price of the call.  As the writer of a covered call option on a foreign currency, a Fund foregoes, during the option’s life, the opportunity to profit from currency appreciation.

If trading were suspended in an option purchased or written by a Fund, the Fund would not be able to close out the option.  If restrictions on exercise were imposed, the Fund might be unable to exercise the option.

Futures Contracts and Options on Futures Contracts.  The Funds may use interest rate futures contracts and index futures contracts.  An interest rate or index futures contract provides for the future sale by one party and purchase by another party of a specified quantity of a financial instrument or the cash value of an index (1) at a specified price and time.  A public market exists in

(1)A futures contract on an index is an agreement pursuant to which two parties agree to take or make delivery of an amount of cash equal to the difference between the value of the index at the close of the last trading day of the contract and the price at which the index contract was originally written.  Although the value of a securities index is a function of the value of certain specified securities, no physical delivery of those securities is made. 

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futures contracts covering a number of indexes (including, but not limited to: the Standard & Poor’s 500 Index; the Value Line Composite Index; the Russell 2000 Index; and the New York Stock Exchange Composite Index) as well as financial instruments (including, but not limited to: U.S. Treasury bonds; U.S. Treasury notes; Eurodollar certificates of deposit; and foreign currencies).  Other index and financial instrument futures contracts are available and it is expected that additional futures contracts will be developed and traded.

The Funds may purchase and write call and put futures options.  Futures options possess many of the same characteristics as options on securities and indexes (discussed above).  A futures option gives the holder the right, in return for the premium paid, to assume a long position (call) or short position (put) in a futures contract at a specified exercise price at any time during the period of the option.  Upon exercise of a call option, the holder acquires a long position in the futures contract and the writer is assigned the opposite short position.  In the case of a put option, the opposite is true.

To the extent required by regulatory authorities having jurisdiction over the Funds, the Funds will limit their use of futures contracts and futures options to hedging transactions.  For example, a Fund might use futures contracts to hedge against fluctuations in the general level of stock prices, anticipated changes in interest rates, or currency fluctuations that might adversely affect either the value of the Fund’s securities or the price of the securities that the Fund intends to purchase.  The Fund’s hedging may include sales of futures contracts as an offset against the effect of expected declines in stock prices or currency exchange rates or increases in interest rates and purchases of futures contracts as an offset against the effect of expected increases in stock prices or currency exchange rates or declines in interest rates.  Although other techniques could be used to reduce the Funds’ exposure to stock price, interest rate, and currency fluctuations, the Funds may be able to hedge their exposure more effectively and perhaps at a lower cost by using futures contracts and futures options.

The success of any hedging technique depends on Columbia WAM’s ability to correctly predict changes in the level and direction of stock prices, interest rates, currency exchange rates, and other factors.  Should those predictions be incorrect, a Fund’s return might have been better had hedging not been attempted; however, in the absence of the ability to hedge, Columbia WAM might have taken portfolio actions in anticipation of the same market movements with similar investment results but, presumably, at greater transaction costs.

When a purchase or sale of a futures contract is made by a Fund, that Fund is required to deposit with its custodian or broker a specified amount of cash or U.S. government securities or other securities acceptable to the broker (“initial margin”).  The margin required for a futures contract is generally set by the exchange on which the contract is traded; however, the margin requirement may be modified during the term of the contract, and the Fund’s broker may require margin deposits in excess of the minimum required by the exchange.  The initial margin is in the nature of a performance bond or good faith deposit on the futures contract, which is returned to the Fund upon termination of the contract, assuming all contractual obligations have been satisfied.  The Funds expect to earn interest income on their initial margin deposits.  A futures contract held by a Fund is valued daily at the official settlement price of the exchange on which it is traded.  Each day the Fund pays or receives cash, called “variation margin,” equal to the daily change in value of the futures contract.  This process is known as “marking-to-market.”  Variation margin paid or received by a Fund does not represent a borrowing or loan by the Fund but is instead settlement between that Fund and the broker of the amount one would owe the other if the futures contract had expired at the close of the previous day.  In computing daily net asset value (“NAV”), the Funds will mark-to-market their open futures positions.

The Funds are also required to deposit and maintain margin with respect to put and call options on futures contracts they write.  Such margin deposits will vary depending on the nature of the underlying futures contract (and the related initial margin requirements), the current market value of the option, and other futures positions held by the Funds.

Although some futures contracts call for making or taking delivery of the underlying securities, usually these obligations are closed out prior to delivery by offsetting purchases or sales of matching futures contracts (same exchange, underlying security or index, and delivery month).  If an offsetting sale price is more than the original purchase price, the Fund engaging in the transaction realizes a capital gain, or if it is less, the Fund realizes a capital loss.  Conversely, if an offsetting purchase price is less than the original sale price, the Fund realizes a capital gain, or if it is more, the Fund realizes a capital loss.  The transaction costs must also be included in these calculations.

Risks Associated with Futures.  There are several risks associated with the use of futures contracts and futures options as hedging techniques.  A purchase or sale of a futures contract may result in losses in excess of the amount invested in the futures contract.  There can be no guarantee that there will be a correlation between price movements in the hedging vehicle and in the portfolio securities being hedged.  In addition, there are significant differences between the securities and futures markets that could result in an imperfect correlation between the markets, causing a given hedge not to achieve its objectives.  The degree of imperfection of correlation depends on circumstances such as: variations in speculative market demand for futures, futures

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options, and the related securities, including technical influences in futures and futures options trading and differences between the Funds’ investments being hedged and the securities underlying the standard contracts available for trading.  For example, in the case of index futures contracts, the composition of the index, including the issuers and the weighting of each issue, may differ from the composition of a Fund’s portfolio, and, in the case of interest rate futures contracts, the interest rate levels, maturities, and creditworthiness of the issues underlying the futures contract may differ from the financial instruments held in a Fund’s portfolio.  A decision as to whether, when, and how to hedge involves the exercise of skill and judgment, and even a well-conceived hedge may be unsuccessful to some degree because of market behavior or unexpected stock price or interest rate trends.

Futures exchanges may limit the amount of fluctuation permitted in certain futures contract prices during a single trading day.  The daily limit establishes the maximum amount that the price of a futures contract may vary either up or down from the previous day’s settlement price at the end of the current trading session.  Once the daily limit has been reached in a futures contract subject to the limit, no more trades may be made on that day at a price beyond that limit.  The daily limit governs only price movements during a particular trading day and therefore does not limit potential losses because the limit may work to prevent the liquidation of unfavorable positions.  For example, futures prices have occasionally moved to the daily limit for several consecutive trading days with little or no trading, thereby preventing prompt liquidation of positions and subjecting some holders of futures contracts to substantial losses.  Stock index futures contracts are not normally subject to such daily price change limitations.

There can be no assurance that a liquid market will exist at a time when a Fund seeks to close out a futures or futures option position.  The Fund would be exposed to possible loss on the position during the interval of inability to close, and would continue to be required to meet margin requirements until the position is closed.  In addition, many of the contracts discussed above are relatively new instruments without a significant trading history.  As a result, there can be no assurance that an active secondary market will develop or continue to exist.

Limitations on Options and Futures.  A Fund (excluding the Portfolio Funds) will not enter into a futures contract or purchase an option thereon if, immediately thereafter, the initial margin deposits for futures contracts held by that Fund plus premiums paid by it for open futures option positions, less the amount by which any such positions are “in-the-money,” (2) would exceed 5% of the Fund’s total assets.

When purchasing a futures contract or writing a put option on a futures contract, a Fund must maintain with its custodian or broker readily-marketable securities having a fair market value (including any margin) at least equal to the market value of such contract.  When writing a call option on a futures contract, a Fund similarly will maintain with its custodian or broker readily-marketable securities having a fair market value (including any margin) at least equal to the amount by which such option is in-the-money until the option expires or is closed out by the Fund.

A Fund may not maintain open short positions in futures contracts, call options written on futures contracts, or call options written on indexes if, in the aggregate, the market value of all such open positions exceeds the current value of the securities in its portfolio, plus or minus unrealized gains and losses on the open positions, adjusted for the historical relative volatility of the relationship between the portfolio and the positions.  For this purpose, to the extent a Fund has written call options on specific securities in its portfolio, the value of those securities will be deducted from the current market value of the securities portfolio.

The CFTC requires the registration of “commodity pool operators,” defined as any person engaged in a business which is of the nature of a company, syndicate or a similar form of enterprise, and who, in connection therewith, solicits, accepts or receives from others, funds, securities or property for the purpose of trading in any commodity for future delivery on or subject to the rules of any contract market.  The CFTC has adopted Rule 4.5, which provides an exclusion from the definition of commodity pool operator for any registered investment company which meets the requirements of the Rule.  Rule 4.5 requires, among other things, that an investment company and its principals or employees wishing to avoid commodity pool operator status claim the exclusion provided in Rule 4.5 by filing a notice of eligibility with both the CFTC and the National Futures Association.  Rule 4.5 does not propose any limitations on investment companies with regard to the use of futures or options on futures.  Before engaging in transactions involving futures contracts, the funds will file such notices and meet the requirements of Rule 4.5, or such other requirements as the CFTC or its staff may from time to time issue, in order to render registration as a commodity pool operator unnecessary.

(2)A call option is “in-the-money” if the value of the futures contract that is the subject of the option exceeds the exercise price.  A put option is “in-the-money” if the exercise price exceeds the value of the futures contract that is the subject of the option.

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Swap Agreements, Caps, Floors and Collars.  A swap agreement is generally individually negotiated and structured to include exposure to one or more of a variety of different types of investments or market factors.  Depending on its structure, a swap agreement may increase or decrease a Fund’s exposure to changes in the value of an index of securities in which the Fund might invest, the value of a particular security or group of securities, or foreign currency values.  Swap agreements can take many different forms and are known by a variety of names.  A Fund may enter into any form of swap agreement if the Adviser determines it is consistent with that Fund’s investment objective and policies, but each Fund (excluding the Portfolio Funds) will limit its use of swap agreements so that no more than 5% of its total assets will be invested in such agreements.

A swap agreement tends to shift a Fund’s investment exposure from one type of investment to another.  For example, if a Fund agrees to exchange payments in dollars at a fixed rate for payments in a foreign currency the amount of which is determined by movements of a foreign securities index, the swap agreement would tend to increase that Fund’s exposure to foreign stock market movements and foreign currencies.  Depending on how it is used, a swap agreement may increase or decrease the overall volatility of a Fund’s investments and its NAV.

The performance of a swap agreement is determined by the change in the specific currency, market index, security, or other factors that determine the amounts of payments due to and from a Fund.  If a swap agreement calls for payments by a Fund, the Fund must be prepared to make such payments when due.  If the counterparty’s creditworthiness declines, the value of a swap agreement would be likely to decline, potentially resulting in a loss.  The Adviser expects to be able to eliminate a Fund’s exposure under any swap agreement either by assignment or by other disposition, or by entering into an offsetting swap agreement with the same party or a similarly creditworthy party.

Some Portfolio Funds may purchase caps, floors and collars.  The purchase of a cap entitles the purchaser to receive payments on a notional principal amount from the party selling the cap to the extent that a specified index exceeds a predetermined interest rate or amount.  The purchase of a floor entitles the purchaser to receive payments on a notional principal amount from the party selling such floor to the extent that a specified index falls below a predetermined interest rate or amount.  A collar is a combination of a cap and floor that preserves a certain return within a predetermined range of interest rates or values.

A Fund will segregate assets to cover its current obligations under a swap agreement, cap, floor or collar.  If a Fund enters into a swap agreement on a net basis, it will segregate assets with a daily value at least equal to the excess, if any, of the Fund’s accumulated obligations under the swap agreement over the accumulated amount the Fund is entitled to receive under the agreement.  If a Fund enters into a swap agreement on other than a net basis, it will segregate assets with a value equal to the full amount of the Fund’s accumulated obligations under the agreement.

Short Sales Against the Box

Each Fund may make short sales of securities if, at all times when a short position is open, the Fund owns an equal amount of such securities or securities convertible into or ex­changeable for, without payment of any further consideration, securities of the same issue as, and equal in amount to, the securities sold short.  This technique is called selling short “against the box.”  Although permitted by its investment restrictions, the Funds do not currently in­tend to sell securities short.

In a short sale against the box, a Fund does not deliver from its portfolio the securi­ties sold and does not receive immediately the proceeds from the short sale.  Instead, the Fund borrows the securities sold short from a broker-dealer through which the short sale is executed, and the broker-dealer delivers those securities, on behalf of the Fund, to the purchaser of the securities.  The broker-dealer is entitled to retain the proceeds from the short sale until the Fund delivers to the broker-dealer the securities sold short.  In addition, the Fund is required to pay to the broker-dealer the amount of any dividends paid on shares sold short.  Finally, to secure its obligation to deliver to the broker-dealer the securities sold short, the Fund must deposit and continuously maintain in a separate account with its custodian an equivalent amount of the securities sold short or securities convertible into or exchangeable for such securities without the payment of additional consideration.  The Fund is said to have a short position in the securities sold until it delivers to the broker-dealer the securities sold, at which time the Fund receives the proceeds of the sale.  Because the Fund ordinarily will want to continue to hold securities in its portfolio that are sold short, the Fund will normally close out a short position by purchasing on the open market and delivering to the broker-dealer an equal amount of the securities sold short, rather than by delivering portfolio securities.

Short sales may protect a Fund against the risk of losses in the value of its portfolio securities because any unrealized losses with respect to such portfolio securities should be wholly or partially offset by a correspond­ing gain in the short position.  However, any poten­tial gains in the portfolio securities should be wholly or partially offset by a corresponding loss in the short position.  The extent to which such gains or losses are off­set will depend upon the amount of securities sold short relative to the

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amount the Fund owns, either directly or in­directly, and, in the case where the Fund owns convertible securities, changes in the conversion premium.  The Funds will incur transaction costs in connection with short sales.

In addition to enabling the Funds to hedge against market risk, a short sale may afford a Fund an opportunity to earn additional current income to the extent the Fund is able to enter into an arrangement with the broker-dealer through which the short sale is executed to receive in­come with respect to the proceeds of the short sale during the period the Fund’s short posi­tion remains open.

Debt Securities

The Funds and some Portfolio Funds may invest in debt securities, including lower-rated securities (i.e., securities rated BB or lower by Standard & Poor’s Corporation, a division of The McGraw-Hill Companies (“S&P”) or Ba or lower by Moody’s Investor Services, Inc. (“Moody’s”), commonly called “junk bonds”), and securities that are not rated.  There are no restrictions as to the ratings of debt securities acquired by the Funds or the portion of a Fund’s assets that may be invested in debt securities in a particular ratings category, except that Columbia Acorn International may not invest more than 20% of its assets in securities rated below investment grade or considered by the Adviser to be of comparable credit quality.  Neither Columbia Acorn Fund nor Columbia Acorn International expects to invest more than 5% of its net assets in such securities during the current fiscal year.  None of Columbia Acorn USA, Columbia Acorn Select and Columbia Acorn International Select intends to invest more than 20% of its total assets in debt securities nor more than 5% of its total assets in securities rated at or lower than the lowest investment grade.  Columbia Thermostat Fund may invest up to 100% of its total assets in Portfolio Funds that invest in debt securities, including lower-rated securities, and securities that are not rated.

Securities rated BBB or Baa are considered to be medium grade and to have speculative characteristics.  Lower-rated debt securities are predominantly speculative with respect to the issuer’s capacity to pay interest and repay principal.  Investment in medium- or lower-quality debt securities involves greater investment risk, including the possibility of issuer default or bankruptcy.  An economic downturn could severely disrupt the market for such securities and adversely affect the value of such securities.  In addition, lower-quality bonds are less sensitive to interest rate changes than higher-quality instruments and generally are more sensitive to adverse economic changes or individual corporate developments.  During a period of adverse economic changes, including a period of rising interest rates, the junk bond market may be severely disrupted, and issuers of such bonds may experience difficulty in servicing their principal and interest payment obligations.

Medium- and lower-quality debt securities may be less marketable than higher-quality debt securities because the market for them is less broad.  The market for unrated debt securities is even narrower.  During periods of thin trading in these markets, the spread between bid and asked prices is likely to increase significantly, and a Fund may have greater difficulty selling its portfolio securities.  The market value of these securities and their liquidity may be affected by adverse publicity and investor perceptions.  A more complete description of the characteristics of bonds in each ratings category is included in Appendix I to this SAI.

Illiquid and Restricted Securities

The Funds (excluding the Portfolio Funds) may not invest in illiquid securities, if as a result they would comprise more than 15% of the value of the net assets of the Fund.  The limit on illiquid securities for each Portfolio Fund is 15%.  An illiquid security generally is one that may not be sold in the ordinary course of business within seven days at approximately the value assigned to it in calculations of a Fund’s net asset value.  Repurchase agreements maturing in more than seven days, OTC derivatives and restricted securities are generally illiquid; other types of investments may also be illiquid from time to time.  If, through the appreciation of illiquid securities or the depreciation of liquid securities, a Fund should be in a position where more than 15% of the value of its net assets are invested in illiquid assets, that Fund will take appropriate steps to protect liquidity.  Illiquid securities are valued at a fair value determined in good faith by the Board of Trustees or its delegate.

Restricted securities may be sold only in privately negotiated transactions or in a public offering with respect to which a registration statement is in effect under the Securities Act of 1933 (the “1933 Act”).  Where registration is required, a Fund may be obligated to pay all or part of the registration expenses and a considerable period may elapse between the time of the decision to sell and the time the Fund may be permitted to sell a security under an effective registration statement.  If, during such a period, adverse market conditions were to develop, the Fund might obtain a less favorable price than prevailed when it decided to sell.  Restricted securities are valued at a fair value determined in good faith by the Board of Trustees or its delegate.  Neither Columbia Acorn Fund, Columbia Acorn International, Columbia Acorn USA nor Columbia Thermostat Fund will invest more than 10% of its total assets (valued at the time of investment) in restricted securities.

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Notwithstanding the above, a Fund may purchase securities that have been privately placed but that are eligible for purchase and sale under Rule 144A under the 1933 Act.  That rule permits certain qualified institutional buyers, such as the Funds, to trade in privately placed securities that have not been registered for sale under the 1933 Act.  The Adviser, under the supervision of the Board of Trustees, will consider whether securities purchased under Rule 144A are illiquid and thus subject to each Fund’s restriction of investing no more than 15% of its assets in illiquid securities.  A determination of whether a Rule 144A security is liquid or not is a question of fact.  In making that determination, the Adviser will consider the trading markets for the specific security taking into account the unregistered nature of a Rule 144A security.  In addition, the Adviser could consider (1) the frequency of trades and quotes, (2) the number of dealers and potential purchasers, (3) the dealer undertakings to make a market, and (4) the nature of the security and of market place trades (e.g., the time needed to dispose of the security, the method of soliciting offers and the mechanics of transfer).  The liquidity of Rule 144A securities would be monitored and if, as a result of changed conditions, it were determined that a Rule 144A security was no longer liquid, a Fund’s holding of the security would be reviewed to determine what, if any, steps were required to assure that the Fund did not invest more than the specified percentage of its assets in illiquid securities.  Investing in Rule 144A securities could have the effect of increasing the amount of a Fund’s assets invested in illiquid securities if qualified institutional buyers were unwilling to purchase such securities.

Repurchase Agreements

A repurchase agreement involves a transaction in which a Fund or Portfolio Fund purchases a security from a bank or recognized securities dealer and simultaneously commits to resell that security to the bank or dealer at an agreed-upon price, date, and market rate of interest unrelated to the coupon rate or maturity of the purchased security.  Although repurchase agreements carry certain risks not associated with direct investments in securities, a Fund will enter into repurchase agreements only with banks, dealers and clearing corporations that the Adviser believes present minimal credit risks in accordance with guidelines approved by the Board of Trustees.  The Adviser will review and monitor the creditworthiness of such institutions, and will consider the capitalization of the institution, the Adviser’s prior dealings with the institution, any rating of the institution’s senior long-term debt by independent rating agencies, and other relevant factors.

A Fund will invest in a repurchase agreement only if it is collateralized at all times in an amount at least equal to the repurchase price plus accrued interest.  To the extent that the proceeds from any sale of such collateral upon a default in the obligation to repurchase were less than the repurchase price, the Fund would suffer a loss.  If the financial institution that is party to the repurchase agreement petitions for bankruptcy or otherwise becomes subject to bankruptcy or other liquidation proceedings, there may be restrictions on the Fund’s ability to sell the collateral and the Fund could suffer a loss.  However, with respect to financial institutions whose bankruptcy or liquidation proceedings are subject to the U.S. Bankruptcy Code, each Fund intends to comply with provisions under such Code that would allow it immediately to resell such collateral.

When-Issued and Delayed Delivery Securities; Reverse Repurchase Agreements

The Funds and Portfolio Funds may purchase securities on a when-issued or delayed delivery basis.  Although the payment and interest terms of these securities are established at the time a Fund enters into the commitment, the securities may be delivered and paid for a month or more after the date of purchase, when their value may have changed.  A Fund makes such commitments only with the intention of actually acquiring the securities, but may sell the securities before the settlement date if the Adviser deems it advisable for investment reasons.  A Fund may utilize spot and forward foreign currency exchange transactions to reduce the risk inherent in fluctuations in the exchange rate between one currency and another when securities are purchased or sold on a when-issued or delayed delivery basis.

A Fund may enter into reverse repurchase agreements with banks and securities dealers.  A reverse repurchase agreement is a repurchase agreement in which the Fund is the seller of, rather than the investor in, securities and agrees to repurchase them at an agreed-upon time and price.  Use of a reverse repurchase agreement may be preferable to a regular sale and later repurchase of securities because it avoids certain market risks and transaction costs.

At the time a Fund enters into a binding obligation to purchase securities on a when-issued basis or enters into a reverse repurchase agreement, assets of the Fund having a value at least as great as the purchase price of the securities to be purchased will be segregated on the books of the Fund and held by the custodian throughout the period of the obligation.  The use of these investment strategies, as well as any borrowing by a Fund, may increase NAV fluctuation.  The Funds have no present intention of investing in reverse repurchase agreements.

Zero Coupon Securities

Some of the Portfolio Funds may invest in zero coupon securities, which are securities issued at a significant discount from face value and do not pay interest at intervals during the life of the security.  Zero coupon securities include securities issued in

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certificates representing undivided interests in the interest or principal of mortgage-backed securities (interest only/principal only), which tend to be more volatile than other types of securities.  The Portfolio Fund will accrue and distribute income from stripped securities and certificates on a current basis and may have to sell securities to generate cash for distributions.

Step Coupon Bonds

Some of the Portfolio Funds may invest in debt securities that pay interest at a series of different rates (including 0%) in accordance with a stated schedule for a series of periods.  In addition to the risks associated with the credit rating of the issuer, these securities may be subject to more volatility risk than fixed rate debt securities.

Tender Option Bonds

Some of the Portfolio Funds may invest in tender option bonds.  A tender option bond is a municipal security (generally held pursuant to a custodial arrangement) having a relatively long maturity and bearing interest at a fixed rate that is substantially higher than prevailing short-term tax-exempt rates and that has been coupled with the agreement of a third party, such as a bank, broker-dealer or other financial institution, who grants the security holder the option, at periodic intervals, to tender the security to it and receive the face value thereof.  As consideration for providing the option, the third party financial institution receives periodic fees equal to the difference between the municipal security’s fixed coupon rate and the rate, as determined by a remarketing or similar agent at or near the commencement of such period, that would cause the securities, coupled with the tender option, to trade at par on the date of such determination.  Thus, after payment of this fee, the security holder effectively holds a demand obligation that bears interest at the prevailing short-term tax-exempt rate.  The Portfolio Fund’s advisor will consider on an ongoing basis the creditworthiness of the issuer of the underlying municipal securities, of any custodian, and of the third-party provider of the tender option.  In certain instances and for certain tender option bonds, the option may be terminable in the event of a default in payment of principal or interest on the underlying municipal securities and for other reasons.

Pay-In-Kind (PIK) Securities

Some Portfolio Funds may invest in securities which pay interest either in cash or additional securities.  These securities are generally high yield securities and, in addition to the other risks associated with investing in high yield securities, are subject to the risks that the interest payments which consist of additional securities are also subject to the risks of high yield securities.

Money Market Instruments

Some Portfolio Funds may invest in money market instruments.  Government obligations are issued by the U.S. or foreign governments, their subdivisions, agencies and instrumentalities.  Supranational obligations are issued by supranational entities and are generally designed to promote economic improvements.  Certificates of deposits are issued against deposits in a commercial bank with a defined return and maturity.  Banker’s acceptances are used to finance the import, export or storage of goods and are “accepted” when guaranteed at maturity by a bank.  Commercial paper is a promissory note issued by businesses to finance short-term needs (including those with floating or variable interest rates, or including a frequent interval put feature).  Short-term corporate obligations are bonds and notes (with one year or less to maturity at the time of purchase) issued by businesses to finance long-term needs.  Participation Interests include the underlying securities and any related guaranty, letter of credit, or collateralization arrangement which some Portfolio Funds would be allowed to invest in directly.

Securities Loans

The Funds may make secured loans of their portfolio securities amounting to not more than the percentage of their total assets specified in “Investment Policies”, thereby realizing additional income.  The risks in lending portfolio securities, as with other extensions of credit, consist of possible delay in recovery of the securities or possible loss of rights in the collateral should the borrower fail financially.  As a matter of policy, securities loans are made to banks and broker-dealers pursuant to agreements requiring that loans be continuously secured by collateral in cash or short-term debt obligations at least equal at all times to the value of the securities on loan.  The borrower pays to the Fund an amount equal to any dividends or interest received on securities lent.  The Fund retains all or a portion of the interest received on investment of the cash collateral or receives a fee from the borrower.  Although voting rights, or rights to consent, with respect to the loaned securities pass to the borrower, the Fund retains the right to call the loans at any time on reasonable notice, and it will do so in order that the securities may be voted by the Fund if the holders of such securities are asked to vote upon or consent to matters materially affecting the investment.  The Fund may also call such loans in order to sell the securities involved.

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Mortgage Dollar Rolls

Some Portfolio Funds may invest in mortgage dollar rolls.  In a mortgage dollar roll, the Portfolio Fund sells a mortgage-backed security and simultaneously enters into a commitment to purchase a similar security at a later date.  The Portfolio Fund either will be paid a fee by the counterparty upon entering into the transaction or will be entitled to purchase the similar security at a discount.  As with any forward commitment, mortgage dollar rolls involve the risk that the counterparty will fail to deliver the new security on the settlement date, which may deprive the fund of obtaining a beneficial investment.  In addition, the security to be delivered in the future may turn out to be inferior to the security sold upon entering into the transaction.  In addition, the transaction costs may exceed the return earned by the Portfolio Fund from the transaction.

Mortgage-Backed Securities

Some of the Portfolio Funds may invest in mortgage-backed securities, including “collateralized mortgage obligations” (CMOs) and “real estate mortgage investment conduits” (REMICs).  Mortgage-backed securities evidence ownership in a pool of mortgage loans made by certain financial institutions that may be insured or guaranteed by the U.S. government or its agencies.  CMOs are obligations issued by special-purpose trusts, secured by mortgages.  REMICs are entities that own mortgages and elect REMIC status under the Internal Revenue Code.  Both CMOs and REMICs issue one or more classes of securities of which one (the Residual) is in the nature of equity.  The Portfolio Funds will not invest in the Residual class.  Principal on mortgage-backed securities, CMOs and REMICs may be prepaid if the underlying mortgages are prepaid.  Prepayment rates for mortgage-backed securities tend to increase as interest rates decline (effectively shortening the security’s life) and decrease as interest rates rise (effectively lengthening the security’s life).  Because of the prepayment feature, these securities may not increase in value as much as other debt securities when interest rates fall.  A Portfolio Fund may be able to invest prepaid principal only at lower yields.  The prepayment of such securities purchased at a premium may result in losses equal to the premium.

Non-Agency Mortgage-Backed Securities

A Portfolio Fund may invest in non-investment grade mortgage-backed securities that are not guaranteed by the U.S. government or an agency.  Such securities are subject to the risks described under “Lower Rated Debt Securities” and “Mortgage-Backed Securities.”  In addition, although the underlying mortgages provide collateral for the security, a Portfolio Fund may experience losses, costs and delays in enforcing its rights if the issuer defaults or enters bankruptcy.

Asset-Backed Securities

Some Portfolio Funds may invest in asset-backed securities.  Asset-backed securities are interests in pools of debt securities backed by various types of loans such as credit card, auto and home equity loans.  These securities involve prepayment risk, which is the possibility that the underlying debt may be refinanced or prepaid prior to maturity during periods of declining interest rates.  During periods of rising interest rates, asset-backed securities have a high risk of declining in price because the declining prepayment rates effectively lengthen the expected maturity of the securities.  A decline in interest rates may lead to a faster rate of repayment on asset-backed securities and, therefore, cause a Portfolio Fund to earn a lower interest rate on reinvestment.  In addition, the potential impact of prepayment on the price of an asset-backed security may be difficult to predict and result in greater volatility.

Municipal Lease Obligations

Some of the Portfolio Funds may invest in municipal lease obligations.  Although a municipal lease obligation does not constitute a general obligation of the municipality for which the municipality’s taxing power is pledged, a municipal lease obligation is ordinarily backed by the municipality’s covenant to budget for, appropriate and make the payments due under the municipal lease obligation.  However, certain lease obligations contain “non-appropriation” clauses which provide that the municipality has no obligation to make lease or installment purchase payments in future years unless money is appropriated for such purpose on a yearly basis.  Although “non-appropriation” lease obligations are secured by the leased property, disposition of the property in the event of foreclosure might prove difficult.  In addition, the tax treatment of such obligations in the event of non-appropriation is unclear.

Determinations concerning the liquidity and appropriate valuation of a municipal lease obligation, as with any other municipal security, are made based on all relevant factors.  These factors include, among others: (1) the frequency of trades and quotes for the obligation; (2) the number of dealers willing to purchase or sell the security and the number of other potential buyers; (3) the willingness of dealers to undertake to make a market in the security; and (4) the nature of the marketplace trades, including the time needed to dispose of the security, the method of soliciting offers, and the mechanics of the transfer.

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Participation Interests

Some Portfolio Funds may invest in municipal obligations either by purchasing them directly or by purchasing certificates of accrual or similar instruments evidencing direct ownership of interest payments or principal payments, or both, on municipal obligations, provided that, in the opinion of counsel to the initial seller of each such certificate or instrument, any discount accruing on such certificate or instrument that is purchased at a yield not greater than the coupon rate of interest on the related municipal obligations will be exempt from federal income tax to the same extent as interest on such municipal obligations.  Some Portfolio Funds may also invest in tax-exempt obligations by purchasing from banks participation interests in all or part of specific holdings of municipal obligations.  Such participations may be backed in whole or part by an irrevocable letter of credit or guarantee of the selling bank.  The selling bank may receive a fee from the Portfolio Fund in connection with the arrangement.  The Portfolio Fund will not purchase such participation interests unless it receives an opinion of counsel or a ruling of the Internal Revenue Service that interest earned by it on municipal obligations in which it holds such participation interests is exempt from regular federal income tax.

Stand-by Commitments

When a Portfolio Fund purchases municipal obligations, it may also acquire stand-by commitments from banks and broker-dealers with respect to such municipal obligations.  A stand-by commitment is the equivalent of a put option acquired by the Portfolio Fund with respect to a particular municipal obligation held in its portfolio.  A stand-by commitment is a security independent of the municipal obligation to which it relates.  The amount payable by a bank or dealer during the time a stand-by commitment is exercisable, absent unusual circumstances relating to a change in market value, would be substantially the same as the value of the underlying municipal obligation.  A stand-by commitment might not be transferable by the Portfolio Fund, although it could sell the underlying municipal obligation to a third party at any time.

Some Portfolio Funds expect that stand-by commitments generally will be available without the payment of direct or indirect consideration.  However, if necessary and advisable, the Portfolio Fund may pay for stand-by commitments either separately in cash or by paying a higher price for portfolio securities which are acquired subject to such a commitment (thus reducing the yield to maturity otherwise available for the same securities).  The total amount paid in either manner for outstanding stand-by commitments held in the fund portfolio will not exceed 10% of the value of the Portfolio Fund’s total assets calculated immediately after each stand-by commitment is acquired.  The Portfolio Fund will enter into stand-by commitments only with banks and broker-dealers that, in the judgment of the Trust’s Board of Trustees, present minimal credit risks.

Inverse Floaters

Some Portfolio Funds may invest in inverse floaters.  Inverse floaters are derivative securities whose interest rates vary inversely to changes in short-term interest rates and whose values fluctuate inversely to changes in long-term interest rates.  The value of certain inverse floaters will fluctuate substantially more in response to a given change in long-term rates than would a traditional debt security.  These securities have investment characteristics similar to leverage, in that interest rate changes have a magnified effect on the value of inverse floaters.

Variable and Floating Rate Obligations

Some of the Portfolio Funds may invest in variable and floating rate securities.  Variable rate instruments provide for periodic adjustments in the interest rate.  Floating rate instruments provide for automatic adjustment of the interest rate whenever some other specified interest rate changes.  Some variable and floating rate obligations are direct lending arrangements between the purchaser and the issuer and there may be no active secondary market.  However, in the case of variable and floating rate obligations with a demand feature, a Fund may demand payment of principal and accrued interest at a time specified in the instrument or may resell the instrument to a third party.  In the event an issuer of a variable or floating rate obligation defaulted on its payment obligation, a Fund might be unable to dispose of the note because of the absence of a secondary market and could, for this or other reasons, suffer a loss to the extent of the default.  Variable or floating rate instruments issued or guaranteed by the U.S. Government or its agencies or instrumentalities are similar in form but may have a more active secondary market.  Substantial holdings of variable and floating rate instruments could reduce portfolio liquidity.

If a variable or floating rate instrument is not rated, the Portfolio Funds’ Adviser must determine that such instrument is comparable to rated instruments eligible for purchase by the Portfolio Fund and will consider the earning power, cash flows and other liquidity ratios of the issuers and guarantors of such instruments and will continuously monitor their financial status in order to meet payment on demand.  In determining average weighted portfolio maturity of each of the Portfolio Fund, a variable or floating rate instrument issued or guaranteed by the U.S. Government or an agency or instrumentality thereof will be deemed to have a maturity equal to the period remaining until the obligation’s next interest rate adjustment.  Variable and floating rate

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obligations with a demand feature will be deemed to have a maturity equal to the longer of the period remaining to the next interest rate adjustment or the demand notice period.

Real Estate Investment Trusts (“REITs”)

Some Portfolio Funds may invest in REITs.  REITs are pooled investment vehicles that invest primarily in real estate, such as shopping centers, malls, multi-family housing, or commercial property, or real-estate related loans such as mortgages.  Investing in REITs involves unique risks and may be affected by changes in the value of the underlying property owned by the REIT or affected by the quality of the credit extended.  REITs are significantly affected by the market for real estate and are subject to many of the same risks associated with direct ownership in real estate.  Furthermore, REITs are dependent upon management skills and subject to heavy cash flow dependency.

Convertible Securities and Warrants

Some Portfolio Funds may purchase convertible securities and warrants.  Convertible debentures are interest-bearing debt securities, typically unsecured, that represent an obligation of the corporation providing the owner with claims to the corporation’s earnings and assets before common and preferred stock owners, generally on par with unsecured creditors.  If unsecured, claims of convertible debenture owners would be inferior to claims of secured debt holders.  Convertible preferred stocks are securities that represent an ownership interest in a corporation providing the owner with claims to the corporation’s earnings and assets before common stock owners, but after bond owners.  Investments by a Portfolio Fund in convertible debentures or convertible preferred stock would be a substitute for an investment in the underlying common stock, primarily either in circumstances where only the convertible security is available in quantities necessary to satisfy the Portfolio Fund’s investment needs (for example, in the case of a new issuance of convertible securities) or where, because of financial market conditions, the conversion price of the convertible security is comparable to the price of the underlying common stock, in which case a preferred position with respect to the corporation’s earnings and assets may be preferable to holding common stock.

Warrants are options to buy a stated number of underlying securities at a specified price any time during the life of the warrants.  The securities underlying these warrants will be the same types of securities that a Portfolio Fund will invest in to achieve its investment objective of capital appreciation.  The purchaser of a warrant expects the market price of the underlying security will exceed the purchase price of the warrant plus the exercise price of the warrant, thus resulting in a profit.  If the warrant expires unexercised (because the market price of the warrant never exceeds the warrant purchase price plus the exercise price of the warrant before the expiration date of the warrant), the purchaser will suffer a loss equal to the purchase price of the warrant.

To the extent the Portfolio Fund known as Columbia Conservative High Yield Fund acquires common stock through exercise of conversion rights or warrants or acceptance of exchange or similar offers, the common stock will not be retained in the portfolio.  Orderly disposition of these equity securities will be made consistent with management’s judgment as to the best obtainable price.

Senior Loans

Senior Loans generally are arranged through private negotiations between a borrower and the lenders represented in each case by one or more agents of the several lenders.  Senior Loans in which some Portfolio Funds may purchase interests generally pay interest at rates that are periodically redetermined by reference to a base lending rate plus a premium.  These base lending rates are generally Prime Rate, LIBOR, the CD rate or other base lending rates used by commercial lenders.  The Senior Loans in the Portfolio Funds’ investment portfolios will at all times have a dollar-weighted average time until next interest rate redetermination of 180 days or less.  Because of prepayment provisions, the actual remaining maturity of Senior Loans may vary substantially from the stated maturity of such loans.

Structured Notes

Some Portfolio Funds may invest in structured notes, including “total rate of return swaps” with rates of return determined by reference to the total rate of return on one or more loans referenced in such notes.  The rate of return on the structured note may be determined by applying a multiplier to the rate of total return on the referenced loan or loans.  Application of a multiplier is comparable to the use of financial leverage, which is a speculative technique.  Leverage magnifies the potential for gain and the risk of loss, because a relatively small decline in the value of a referenced note could result in a relatively large loss in the value of structured note.  Structured notes are treated as Senior Loans.

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Temporary Strategies

The Funds have the flexibility to respond promptly to changes in market and economic conditions.  In the interest of preserving shareholders’ capital, the Adviser may employ a temporary defensive investment strategy if it determines such a strategy to be warranted.  Pursuant to such a defensive strategy, a Fund temporarily may hold cash (U.S. dollars, foreign currencies, multinational currency units) and/or invest up to 100% of its assets in high quality debt securities or money market instruments of domestic issuers (or, in the case of Columbia Acorn Fund, Columbia Acorn International, Columbia Acorn International Select and Columbia Thermostat Fund, those of foreign issuers), and most or all of the Fund’s  investments may be made in the United States and denominated in U.S. dollars.  It is impossible to predict whether, when, or for how long a Fund might employ defensive strategies.

In addition, pending investment of proceeds from new sales of Fund shares or to meet ordinary daily cash needs, a Fund temporarily may hold cash (U.S. dollars, foreign currencies, or multinational currency units) and may invest any portion of its assets in money market instruments.

Line of Credit

Columbia Acorn maintains a line of credit with a group of banks in order to permit borrowing on a temporary basis to meet share redemption requests in circumstances in which temporary borrowing may be preferable to liquidation of portfolio securities.  Any borrowings under that line of credit by the Funds would be subject to each Fund’s restrictions on borrowing under “Investment Policies” above.

TAXES – GENERAL

In this section, all discussions of taxation at the shareholder and Fund levels relate to U.S. federal taxes only.  Consult your tax advisor for state, local and foreign tax considerations and for information about special tax considerations that may apply to shareholders that are not natural persons or not U.S. citizens or resident aliens.

Federal Taxes.  Although it may be one of several series in a single trust, each Fund is treated as a separate entity for federal income tax purposes under the Internal Revenue Code of 1986, as amended (“Code”).  Each Fund has elected to be, and intends to qualify to be treated each year as, a “regulated investment company” under Subchapter M of the Code by meeting all applicable requirements of Subchapter M, including requirements as to the nature of the Fund’s gross income, the amount of its distributions (as a percentage of both its overall income and any tax-exempt income), and the composition of its portfolio assets.

To qualify as a “regulated investment company,” a Fund must (a) derive at least 90% of its gross income from dividends, interest, payments with respect to certain securities loans, gains from the sale or other disposition of stock, securities or foreign currencies or other income (including, but not limited to, gains from options, futures or forward contracts) derived with respect to its business of investing in such stock, securities or currencies; (b) diversify its holdings so that, at the close of each quarter of its taxable year, (i) at least 50% of the market value of its total assets consists of cash, cash items, U.S. government securities, securities of other regulated investment companies and other securities limited generally with respect to any one issuer to not more than 5% of the total assets of the Fund and not more than 10% of the outstanding voting securities of such issuer, and (ii) not more than 25% of the value of its total assets is invested in the securities of any issuer (other than U.S. government securities or other regulated investment companies); or of two or more issuers which the Fund controls and which are engaged in the same, similar, or related trades or businesses; and (c) distribute with respect to each year at least 90% of its taxable net investment income, its tax-exempt interest income and the excess, if any, of net short-term capital gains over net long-term capital losses for such year.  In general, for purposes of the 90% gross income requirement described in (a) above, income derived from a partnership will be treated as qualifying income only to the extent such income is attributable to items of income of the partnership which would be qualifying income if realized by the regulated investment company.  However, the American Jobs Creation Act of 2004 (the “2004 Act”), provides that for taxable years of a regulated investment company beginning after October 22, 2004, 100% of the net income derived from an interest in a “qualified publicly traded partnership” (defined as a partnership (i) interests in which are traded on an established securities market or readily tradable on a secondary market or the substantial equivalent thereof and (ii) that derives less than 90% of its income from the qualifying income described in (a) above) will be treated as qualifying income.  In addition, although in general the passive loss rules of the Code do not apply to regulated investment companies, such rules do apply to a regulated investment company with respect to items attributable to an interest in a qualified publicly traded partnership.  Finally, for purposes of (c) above, the term “outstanding voting securities of such issuer” will include the equity securities of a qualified publicly traded partnership.  As a regulated investment company that is accorded special tax treatment, each Fund will not be subject to any federal income taxes on its net investment income and net realized capital gains that it distributes to shareholders on the form of dividends and in accordance with the timing requirements imposed by the Code.  A Fund’s foreign-source income, if any, may be subject to foreign withholding taxes.  If a Fund were to fail to

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qualify as a “regulated investment company” in any taxable year, it would incur a regular federal corporate income tax on all of its taxable income, whether or not distributed, and Fund distributions (including any distributions of net tax-exempt income and net long-term capital gains) would generally be taxable as ordinary income to the shareholders, except to the extent they were treated as “qualified dividend income,” as described below.  In addition, a Fund could be required to recognize unrealized gains, pay substantial taxes and interest and make substantial distributions before requalifying as a regulated investment company.

If a Fund fails to distribute in a calendar year substantially all of its ordinary income for such year and substantially all of its capital gain net income for the one-year period ending October 31 (or later if the Fund is permitted so to elect and so elects), plus any retained amount from the prior year, the Fund will be subject to a 4% excise tax on the underdistributed amounts.  A dividend paid to shareholders by a Fund in January of a year generally is deemed for federal income tax purposes to have been paid by the Fund on December 31 of the preceding year, if the dividend was declared and payable to shareholders of record on a date in October, November or December of that preceding year.  Each Fund intends generally to make distributions sufficient to avoid imposition of the 4% excise tax.

Alternative Minimum Tax.  Distributions derived from interest that is exempt from regular federal income tax may subject corporate shareholders to or increase their liability under the corporate alternative minimum tax (AMT).  A portion of such distributions may constitute a tax preference item for individual shareholders and may subject them to or increase their liability under the AMT.

Dividends Received Deductions.  Income dividends paid by a Fund to its shareholders will qualify for the corporate dividends received deduction only to the extent that dividends earned by the Fund qualify.  Any such dividends, however,  may be includable in adjusted current earnings for purposes of computing corporate AMT.  The dividends received deduction for eligible dividends is subject to a holding period requirement.

Dividends paid by Columbia Acorn International and Columbia Acorn International Select are generally not eligible for the dividends received deduction for corporate shareholders because little or none of those Funds’ income consists of dividends paid by United States corporations.  A portion of the dividends paid by Columbia Acorn Fund, Columbia Acorn USA, Columbia Acorn Select and  Columbia Thermostat Fund is generally eligible for the dividends-received deduction.  Capital gain distributions paid from the Funds are never eligible for this deduction.

Return of Capital Distributions.  If a Fund makes a distribution to a shareholder in excess of the Fund’s current and accumulated “earning and profits” in any taxable year, the excess distribution will be treated as a return of capital to the extent of the shareholder’s tax basis in his or her shares, and thereafter as capital gain.  A return of capital is not taxable, but it reduces tax basis in shares, thus reducing any loss or increasing any gain on a subsequent taxable disposition of such shares.  Dividends and distributions on a Fund’s shares are generally subject to federal income tax as described herein to the extent they do not exceed the Fund’s realized income and gains, even though such dividends and distributions may economically represent a return of a particular shareholder’s investment.  Such distributions are likely to occur in respect of shares purchased at a time when a Fund’s net asset value reflects gains that are either unrealized, or realized but not distributed.  Such realized gains may be required to be distributed even when a Fund’s net asset value also reflects unrealized losses.

Fund Distributions.  Distributions from a Fund (other than qualified dividend income and exempt-interest dividends, as discussed below) will generally be taxable to shareholders as ordinary income to the extent derived from the Fund’s net investment income and net short-term gains.  Distributions of long-term capital gains (that is, the excess of net gains from capital assets held for more than one year over net losses from capital assets held for not more than one year) will be taxable to shareholders as such, regardless of how long a shareholder has held shares in the Fund.  In general, any distributions of net capital gains will be taxed to shareholders who are individuals at a maximum rate of 15% for taxable years beginning on or before December 31, 2008.

All income and capital gains received by Columbia Thermostat Fund from a Portfolio Fund that it owns will be distributed by the Fund (after deductions from the Fund’s allowable losses and expenses) and will be taxable to shareholders as described above.  Because Columbia Thermostat Fund is actively managed, it may realize taxable net short-term capital gains by selling shares of a Portfolio Fund it owns with unrealized appreciation or capital losses which might be disallowed under wash sale rules or recharacterized.  Accordingly, investing in Columbia Thermostat Fund rather than directly investing in the Portfolio Funds may result in accumulated tax liability to a shareholder since the Fund must distribute its net realized gains in accordance with those rules.

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Distributions are taxable to shareholders even if they are paid from income or gains earned by the Fund before a shareholder’s investment (and thus were included in the price the shareholder paid).  Distributions are taxable whether received in cash or in Fund shares.

U.S. Government Securities.  Many states grant tax-free status to dividends paid to a Fund’s shareholders from interest income earned by the Fund from direct obligations of the U.S. government.  Investments in mortgage-backed securities (including GNMA, FNMA and FHLMC Securities) and repurchase agreements collateralized by U.S. government securities do not qualify as direct federal obligations in most states.  Shareholders should consult with their own tax advisors about the applicability of state and local intangible property, income or other taxes to their Fund shares and distributions and redemption proceeds received from a Fund.

Qualified Dividend Income.  For taxable years beginning on or before December 31, 2008, “qualified dividend income” received by an individual will be taxed at the rates applicable to long-term capital gain.  In order for some portion of the dividends received by a Fund shareholder to be qualified dividend income, the Fund must meet holding period and other requirements with respect to some portion of the dividend paying stocks in its portfolio and the shareholder must meet holding period and other requirements with respect to the Fund’s shares.  A dividend will not be treated as qualified dividend income (at either the Fund or shareholder level) (1) if the dividend is received with respect to any share of stock held for fewer than 61 days during the 121-day period beginning on the date which is 60 days before the date on which such share becomes ex-dividend with respect to such dividend (or, in the case of certain preferred stock, 91 days during the 181-day period beginning 90 days before such date), (2) to the extent that the recipient is under an obligation (whether pursuant to a short sale or otherwise) to make related payments with respect to positions in substantially similar or related property, (3) if the recipient elects to have the dividend income treated as investment income for purposes of the limitation on deductibility of investment interest, or (4) if the dividend is received from a foreign corporation that is (a) not eligible for the benefits of a comprehensive income tax treaty with the United States (with the exception of dividends paid on stock of such a foreign corporation readily tradable on an established securities market in the United States) or (b) treated as a passive foreign investment company.

In general, distributions of investment income properly designated by a Fund as derived from qualified dividend income may be treated as qualified dividend income by a shareholder taxed as an individual provided the shareholder meets the holding period and other requirements described above with respect to his or her shares.  If the aggregate qualified dividends received by a Fund during any taxable year are 95% or more of its gross income, then 100% of the Fund’s dividends (other than properly designated capital gain dividends) will be eligible to be treated as qualified dividend income.  For this purpose, the only gain included in the term “gross income” is the excess of net short-term capital gain over net long-term capital loss.

Sales of Shares.  The sale, exchange or redemption of Fund shares may give rise to a gain or loss.  In general, any gain realized upon a taxable disposition of shares will be treated as long-term capital gain if the shares have been held for more than one year.  If held for a shorter period,  the gain on the sale, exchange or redemption of Fund shares will be treated as short-term capital gain.  In general, any loss realized upon a taxable disposition of shares will be treated as long-term loss if the shares have been held more than one year, and otherwise as short-term loss.  However, any loss realized upon a taxable disposition of shares held for six months or less will be disallowed for federal income tax purposes to the extent of any exempt-interest dividends received on such shares.  In addition, any loss not already disallowed as provided in the preceding sentence realized upon a taxable disposition of shares held for six months or less will be treated as long-term, rather than short-term, capital loss to the extent of any long-term capital gain distributions received by the shareholder with respect to those shares.  All or a portion of any loss realized upon a taxable disposition of shares will be disallowed if other shares are purchased within 30 days before or after the disposition.  In such a case, the basis of the newly purchased shares will be adjusted to reflect the disallowed loss.

Under Treasury regulations, if on a disposition of Fund shares a shareholder recognizes a loss of $2 million or more for an individual shareholder or $10 million or more for a corporate shareholder, the shareholder will likely have to file with the Internal Revenue Service a disclosure statement on Form 8886.  Direct shareholders of portfolio securities are in many cases excepted from this reporting requirement, but under current guidance, shareholders of a regulated investment company are not excepted.  Future guidance may extend the current exception from this reporting requirement to shareholders of most or all regulated investment companies.  The fact that a loss is reportable under those regulations does not affect the legal determination of whether the taxpayer’s treatment of the loss is proper.  You are advised to consult your tax advisor.

Backup Withholding.  Certain distributions and redemptions may be subject to backup withholding for taxpayers who fail to furnish a correct taxpayer identification number, who have under-reported dividend or interest income, or who fail to certify to a Fund that the shareholder is a United States person and is not subject to the withholding.  That number and certification may be provided by either a Form W-9 or the share purchase application.  In certain instances, CMS may be notified by the Internal

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Revenue Service that a shareholder is subject to backup withholding.  The backup withholding rate is 28% for amounts paid through 2010.  This backup withholding rate will be 31% for amounts paid after December 31, 2010.

Hedging Transactions.  If a Fund engages in hedging transactions, including hedging transactions in options, futures contracts, and straddles, or other similar transactions, it will be subject to special tax rules (including constructive sale, mark-to-market, straddle, wash sale, and short sale rules), the effect of which may be to accelerate income to the Fund, defer losses to the Fund, cause adjustments in the holding periods of the Fund’s securities, convert long-term capital gains into short-term capital gains or convert short-term capital losses into long-term capital losses.  These rules could therefore affect the amount, timing and character of distributions to shareholders.  Each Fund will endeavor to make any available elections pertaining to such transactions in a manner believed to be in the best interests of the Fund and its shareholders.

Options and Futures.  If a Fund exercises a call or put option that it holds, the premium paid for the option is added to the cost basis of the security purchased (call) or deducted from the proceeds of the security sold (put).  For cash settlement options and futures options exercised by a Fund, the difference between the cash received at exercise and the premium paid is a capital gain or loss.

If a call or put option written by a Fund is exercised, the premium is included in the proceeds of the sale of the underlying security (call) or reduces the cost basis of the security purchased (put).  For cash settlement options and futures options written by a Fund, the difference between the cash paid at exercise and the premium received is a capital gain or loss.

Entry into a closing purchase transaction will result in capital gain or loss.  If an option written by a Fund is in-the-money at the time it was written and the security covering the option was held for more than the long-term holding period prior to the writing of the option, any loss realized as a result of a closing purchase transaction will be long-term.  The holding period of the securities covering an in-the-money option will not include the period of time the option is outstanding.

If a Fund writes an equity call option(3) other than a “qualified covered call option,” as defined in the Internal Revenue Code, any loss on such option transaction, to the extent it does not exceed the unrealized gains on the securities covering the option, may be subject to deferral until the securities covering the option have been sold.

A futures contract held until delivery results in capital gain or loss equal to the difference between the price at which the futures contract was entered into and the settlement price on the earlier of delivery notice date or expiration date.  If a Fund delivers securities under a futures contract, the Fund also realizes a capital gain or loss on those securities.

For federal income tax purposes, a Fund generally is required to recognize for each taxable year its net unrealized gains and losses as of the end of the year on futures, futures options and non-equity options positions held (“year-end mark-to-market”).  Generally, any gain or loss recognized with respect to such positions (either by year-end mark-to-market or by actual closing of the positions) is considered to be 60% long-term and 40% short-term, without regard to the holding periods of the contracts.  However, in the case of positions classified as part of a “mixed straddle,” the recognition of losses on certain positions (including options, futures and options on futures, the related securities and certain successor positions thereto) may be deferred to a later taxable year.  Sale of futures contracts or writing of call options (or futures call options) or purchase of put options (or futures put options) that are intended to hedge against a change in the value of securities held by a Fund may affect the holding period of the hedged securities.

If a Fund were to enter into a short index future, short index futures option or short index option position and the Fund’s portfolio were deemed to “mimic” the performance of the index underlying such contract, the option or futures contract position and the Fund’s stock positions may be deemed to be positions in a mixed straddle, subject to the above-mentioned loss deferral rules.

The Internal Revenue Code imposes constructive sale treatment for federal income tax purposes on certain hedging strategies with respect to appreciated securities.  Under these rules taxpayers will recognize gain, but not loss, with respect to securities if

(3)An equity option is defined to mean any option to buy or sell stock, and any other option the value of which is determined by reference to an index of stocks of the type that is ineligible to be traded on a commodity futures exchange (e.g., an option contract on a sub-index based on the price of nine hotel-casino stocks).  The definition of equity option excludes options on broad-based stock indexes (such as the Standard & Poor’s 500 index).

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they enter into short sales or “offsetting notional principal contracts” (as defined by the Code) with respect to, or futures or “forward contracts” (as defined by the Code) with respect to, the same or substantially identical property, or if they enter into such transactions and then acquire the same or substantially identical property.  The Secretary of the Treasury is authorized to promulgate regulations that will treat as constructive sales certain transactions that have substantially the same effect as short sales, offsetting notional principal contracts, and futures or forward contracts to deliver the same or substantially similar property.

In order for a Fund to continue to qualify for federal income tax treatment as a regulated investment company, at least 90% of the Fund’s gross income for a taxable year must be derived from qualifying income, i.e., dividends, interest, income derived from loans of securities, and gains from the sale of securities or foreign currencies, or other income (including but not limited to gains from options, futures, or forward contracts) derived with respect to its business of investing in such stock, securities, or commodities, and with income derived from an interest in a qualified publicly traded partnership  Any net gain realized from futures (or futures options) contracts will be considered gain from the sale of securities and therefore be qualifying income for purposes of the 90% requirement.

Each Fund intends to distribute to shareholders annually any capital gains that have been recognized for federal income tax purposes (including year-end mark-to-market gains) on options and futures transactions, together with gains on other Fund investments, to the extent such gains exceed recognized capital losses and any net capital loss carryovers of the Fund.  Shareholders will be advised of the nature of such capital gain distributions.

Securities Issued at a Discount.  A Fund’s investment in debt securities issued at a discount and certain other obligations will (and investments in securities purchased at a discount may) require the Fund to accrue and distribute income not yet received.  In such cases, the Fund may be required to sell assets (including when it is not advantageous to do so) to generate the cash necessary to distribute as dividends to its shareholders all of its income and gains and therefore to eliminate any tax liability at the Fund level.

Foreign Currency-Denominated Securities and Related Hedging Transactions.  A Fund’s transactions in foreign currencies, foreign currency-denominated debt securities, certain foreign currency options, futures contracts and forward contracts (and similar instruments) may give rise to ordinary income or loss to the extent such income or loss results from fluctuations in the value of the foreign currency concerned.  This may produce a difference between the Fund’s book income and its taxable income possibly accelerating distributions or converting distributions of book income and gains to returns at capital for book purposes.

If more than 50% of the Fund’s total assets at the end of its fiscal year are invested in stock or securities of foreign corporate issuers, the Fund may make an election permitting its shareholders to take a deduction or credit for federal tax purposes for their pro rata portion of certain qualified foreign taxes paid by the Fund to foreign countries in respect of foreign securities the Fund has held for at least the minimum period specified in the Code.  The Adviser will consider the value of the benefit to a typical shareholder, the cost to a Fund of compliance with the election, and incidental costs to shareholders in deciding whether to make the election.  A shareholder’s ability to claim such a foreign tax credit or deduction in respect of foreign taxes will be subject to certain limitations imposed by the Code, including a holding period requirement, as a result of which a shareholder may not get a full credit or deduction for the amount of foreign taxes so paid by the Fund.  Shareholders who do not itemize on their federal income tax returns may claim a credit (but not a deduction) for such foreign taxes.

Each of Columbia Acorn International and Columbia Acorn International Select intends to meet the requirements of the Code to “pass through” to its shareholders foreign income taxes paid, but there can be no assurance that it will be able to do so.  Each shareholder will be notified within 60 days after the close of each taxable year of Columbia Acorn International or Columbia Acorn International Select, if the foreign taxes paid by the Fund will “pass through” for that year, and, if so, the amount of each shareholder’s pro rata share (by country) of (i) the foreign taxes paid, and (ii) the Fund’s gross income from foreign sources.  Shareholders who are not liable for federal income taxes, including retirement plans qualified under Section 401 of the Code, will not be affected by any such “pass through” of foreign tax credits.  Columbia Acorn Fund, Columbia Acorn USA, Columbia Acorn Select and Columbia Thermostat Fund do not expect to be able to “pass through” foreign tax credits or deductions.

Investment by a Fund in certain “passive foreign investment companies” could subject the Fund to a U.S. federal income tax or other charge on the proceeds from the sale of its investment in such a company; however, this tax can be avoided by making an election to mark such investments to market annually or to treat the passive foreign investment company as a “qualified electing Fund.”  A “passive foreign investment company” is any foreign corporation:  (i) 75 percent or more of the income of which for the taxable year is passive income, or (ii) the average percentage of the assets of which (generally by value, but by adjusted tax basis in certain cases) that produce or are held for the production of passive income is at least 50 percent.  Generally, passive income for this purpose means dividends, interest (including income equivalent to interest), royalties, rents, annuities, the excess

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of gain over losses from certain property transactions and commodities transactions, and foreign currency gains.  Passive income for this purpose does not include rents and royalties received by the foreign corporation from active business and certain income received from related persons.

MANAGEMENT OF THE TRUST

Columbia WAM, CMS and CMD are subsidiaries of Columbia Management Group, LLC (“Columbia Management”) that in turn are indirect wholly owned subsidiaries of Bank of America Corporation.  The investment portfolios (“Columbia Funds”) managed by subsidiaries of Columbia Management are diversified by asset classes, with approximately 50 percent in equity, 30 percent in fixed income, and 20 percent in money market funds.  Columbia Management is located at 100 Federal Street, Boston, MA 02110.  Bank of America Corporation, which trades on the New York Stock Exchange under the symbol “BAC”, is located at 100 North Tryon Street, Charlotte, NC 28255.

Trustees and Officers.  The Board of Trustees has overall management responsibility for the Funds.  Each Trustee serves a term of unlimited duration, provided that a majority of Trustees always has been elected by shareholders.  However, it is expected that every five years the Trustees will call a meeting of shareholders to elect Trustees.  The retirement age for Trustees is 75.  The Trustees appoint their own successors, provided that at least two-thirds of the Trustees, after such appointment, have been elected by shareholders.  Shareholders may remove a Trustee, with or without cause, upon the vote of two-thirds of the Trust’s outstanding shares at any meeting called for that purpose.  A Trustee may be removed with or without cause upon the vote of a majority of the Trustees.

With respect to Columbia Thermostat Fund, certain of the officers of the Trust also serve as officers of the Underlying Trusts.  In addition, the Adviser serves as investment adviser to certain of the Portfolio Funds.  Conflicts may arise as those persons seek to fulfill their fiduciary responsibilities at both levels.

The names of the Trustees and officers of the Trust, the date each was first elected or appointed to office, their principal business occupations during at least the last five years and other directorships they hold, are shown below.  Each Trustee also serves as a trustee of Wanger Advisors Trust, another open-end investment company, consisting of four portfolios managed by Columbia WAM.   

Name, Position(s) with Columbia Acorn and Age at January 1, 2007	Year First Elected or Appointed to Office*	Principal Occupation(s) during Past Five Years	Number of Portfolios in Fund Complex Overseen by Trustee/Officer	Other Directorships
Trustees who are not interested persons of Columbia Acorn:
Margaret Eisen, 53, Trustee	2002	Managing Director, CFA Institute since 2005; Chief Investment Officer, EAM International LLC (corporate finance and asset management) since 2003; prior thereto, managing director, DeGuardiola Advisors (investment bank); formerly managing director, North American Equities at General Motors Asset Management, and director, Worldwide Pension Investments for DuPont Asset Management.	10	Antigenics, Inc. (biotechnology and pharmaceuticals); Wanger Advisors Trust
Jerome Kahn, Jr., 72, Trustee	1987	Portfolio manager and stock analyst and former president, William Harris Investors, Inc. (investment adviser).	10	Wanger Advisors Trust
Steven N. Kaplan, 47, Trustee	1999	Neubauer Family Professor of Entrepreneurship and Finance, Graduate School of Business, University of Chicago.	10	Morningstar, Inc. (provider of independent investment research); Wanger Advisors Trust

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Name, Position(s) with Columbia Acorn and Age at January 1, 2007	Year First Elected or Appointed to Office*	Principal Occupation(s) during Past Five Years	Number of Portfolios in Fund Complex Overseen by Trustee/Officer	Other Directorships
David C. Kleinman, 71, Trustee	1972	Adjunct professor of strategic management, University of Chicago Graduate School of Business; Business consultant.	10	Sonic Foundry, Inc. (rich media systems and software); Wanger Advisors Trust
Allan B. Muchin, 70, Trustee and Vice Chairman	1998	Chairman emeritus, Katten Muchin Rosenman LLP (law firm).	10	Wanger Advisors Trust
Robert E. Nason, 70, Trustee and Chairman	1998	Consultant and private investor.	10	Wanger Advisors Trust
James A. Star, 45, Trustee	2006	President, Longview Asset Management LLC (investment adviser) since 2003, prior thereto, portfolio manager; vice president, Henry Crown and Company (investment firm); president and chief investment officer, Star Partners (hedge fund) from 1998 to 2003.	10	Wanger Advisors Trust
Patricia H. Werhane, 71, (1) Trustee	2006	Ruffin Professor of Business Ethics, Darden Graduate School of Business Administration, University of Virginia since 1993; Senior Fellow of the Olsson Center for Applied Ethics, Darden Graduate School of Business Administration, University of Virginia since 2001; and Wicklander Chair of Business Ethics and Director of the Institute for Business and Professional Ethics, DePaul University since September 2003.	10	Wanger Advisors Trust
John A. Wing, 71, Trustee	2002	Partner, Dancing Lion Partners (investment partnership); prior thereto, Frank Wakely Gunsaulus Professor of Law and Finance, and chairman of the Center for the Study of Law and Financial Markets, Illinois Institute of Technology; formerly chairman of the board and chief executive officer of ABN-AMRO Incorporated (formerly named The Chicago Corporation, a financial services firm) and chief executive officer of Market Liquidity Network, LLC.	10	First Chicago Bank and Trust; First Chicago Bancorp; Wanger Advisors Trust

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Name, Position(s) with Columbia Acorn and Age at January 1, 2007	Year First Elected or Appointed to Office*	Principal Occupation(s) during Past Five Years	Number of Portfolios in Fund Complex Overseen by Trustee/Officer	Other Directorships
Trustees who are interested persons of Columbia Acorn:
Charles P. McQuaid, 53, Trustee and President (2)	1992	President and Chief Investment Officer, CWAM since October 2003; portfolio manager since 1995 and director of research, CWAM and its predecessor from July 1992 through December 2003; interim director of international research, CWAM from October 2003 to December 2004; president since September 2003 and previously senior vice president of Wanger Advisors Trust.	10	Wanger Advisors Trust
Ralph Wanger, 72, Trustee (3)	1970	Founder, former president, chief investment officer and portfolio manager, CWAM from July 1992 to September 2003; former president, Columbia Acorn Trust from April 1992 through September 2003; former president, Wanger Advisors Trust 1994 through September 2003; director, Wanger Investment Company PLC; advisor to CWAM from September 2003 to September 2005.	10	Wanger Advisors Trust

Name, Position(s) with Columbia Acorn and Age at January 1, 2007	Year First Elected or Appointed to Office*	Principal Occupation(s) during Past Five Years	Number of Portfolios in Fund Complex Overseen By Officer	Other Directorships
Officers of Columbia Acorn:
Ben Andrews, 40, Vice President	2004	Analyst and portfolio manager, CWAM since 1998; vice president, Wanger Advisors Trust.	10	None.
Michael G. Clarke, 37, Assistant Treasurer	2004	Assistant treasurer, Wanger Advisors Trust; chief accounting officer and assistant treasurer of the Columbia Funds since October 2004; managing director of CWAM since February 2001; controller of the Columbia Funds, Liberty Funds, Stein Roe Funds and All-Star Funds from May 2004 to October 2004 and assistant treasurer from June 2002 to May 2004; vice president, Product Strategy & Development of the Liberty Funds and Stein Roe Funds from February 2001 to June 2002.	155	None.

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Name, Position(s) with Columbia Acorn and Age at January 1, 2007	Year First Elected or Appointed to Office*	Principal Occupation(s) during Past Five Years	Number of Portfolios in Fund Complex Overseen by Officer	Other Directorships
Jeffrey Coleman, 37, Assistant Treasurer	2006	Assistant Treasurer, Wanger Advisors Trust since March 2006; Group Operations Manager, CWAM since October 2004; vice president of CDC IXIS Asset Management Services, Inc. (investment management) from August 2000 to September 2004.	155	None.
J. Kevin Connaughton, 42, Assistant Treasurer	2001	Treasurer and Chief Financial Officer of the Columbia Funds since December 2000 and of the Liberty All-Star Funds from December 2000 to December 2006; managing director of Columbia’s Fund Administration Group since December 2000; director of Global Liquidity Fund LLC and Bank of America Capital Management LLC since September 2004; assistant treasurer of Wanger Advisors Trust since 2001; treasurer of the Galaxy Funds from September 2002 through November 2005; treasurer, Columbia Management Multi-Strategy Hedge Fund, LLC from December 2002 through December 2004.	155	None.
P. Zachary Egan, 38, Vice President	2003	Director of international research, Columbia WAM, since December 2004; analyst and portfolio manager, Columbia WAM since 1999; prior thereto, a research fellow with the Robert Bosch Foundation.	6	None.
Peter T. Fariel, 49, Assistant Secretary	2006	Associate General Counsel, Bank of America since April 2005; prior thereto, Partner, Goodwin Procter LLP (law firm).	155	None.
John Kunka, 35, Assistant Treasurer	2006	Director of Accounting and Operations, CWAM, since May 2006; assistant treasurer, Wanger Advisors Trust, since 2006; Manager of Mutual Fund Operations, Calamos Advisors, Inc. from September 2005 to May 2006; prior thereto, Manager of Mutual Fund Administration, Van Kampen Investments.	10	None.
Joseph LaPalm, 36, Vice President	2006	Chief compliance officer, CWAM since 2005; vice president, Wanger Advisors Trust since 2006; prior thereto, compliance officer, William Blair & Company (investment firm).	10	None.

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Name, Position(s) with Columbia Acorn and Age at January 1, 2007	Year First Elected or Appointed to Office*	Principal Occupation(s) during Past Five Years	Number of Portfolios in Fund Complex Overseen by Officer	Other Directorships
Bruce H. Lauer, 49, Vice President, Secretary and Treasurer	1995	Chief operating officer, CWAM since April 1995; vice president, treasurer and secretary, Columbia Acorn Trust since 1995; director, Wanger Investment Company PLC; director, Banc of America Capital Management (Ireland) Ltd.	10	None.
Louis J. Mendes, 42, Vice President	2003	Analyst and portfolio manager, CWAM since 2001; vice president, Wanger Advisors Trust; prior thereto, analyst and portfolio manager, Merrill Lynch (investment firm).	10	None.
Robert A. Mohn, 45, Vice President	1997	Analyst and portfolio manager, CWAM since August 1992; director of domestic research, CWAM since March 2004; vice president, Wanger Advisors Trust.	10	None.
Christopher Olson, 41, Vice President	2001	Analyst and portfolio manager, CWAM since January 2001; vice president, Wanger Advisors Trust.	10	None.
Robert Scales, 54, Chief Compliance Officer, Senior Vice President and General Counsel	2004	Senior vice president, chief legal officer and general counsel, Wanger Advisors Trust since 2004; prior thereto, Associate General Counsel, Grant Thornton LLP.	10	None.
Linda Roth-Wiszowaty, 37, Assistant Secretary	2006	Assistant secretary, Wanger Advisors Trust; executive administrator, CWAM since April 2004; prior thereto, executive assistant to the Chief Operating Officer, CWAM.	10	None.

*Dates prior to April 1992 correspond to the date first elected or appointed as a director or officer of The Acorn Fund Inc., the Trust’s predecessor.

(1)Ms. Werhane will be serving as a trustee through September 2007.

(2)Trustee who is an “interested person” of the Trust and of Columbia WAM, as defined in the 1940 Act, because he is an officer of the Trust and Columbia WAM.

(3)Trustee who is treated as an “interested person” of the Trust and of Columbia WAM, as defined in the 1940 Act, because he is a former officer of the Trust, former employee of Columbia WAM and former consultant to Columbia WAM.

The address for the trustees and officers of the Trust is Columbia Wanger Asset Management, L.P., 227 West Monroe Street, Suite 3000, Chicago, Illinois 60606, except for Messrs. Clarke, Coleman, Connaughton and Fariel, whose address is Columbia Management Group, LLC, Mail Stop:  MA5-515-11-05, One Financial Center, Boston, MA 02111.

The following table sets forth the total compensation (including any amounts deferred, as described below) paid by the Trust during the fiscal year ended December 31, 2006 to each of the Trustees of the Trust:  

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Compensation Table

Name of Trustee	Aggregate Compensation  from the Funds (2)(3)		Total Compensation from the Complex(1)(2)
Trustees who are not interested persons of Columbia Acorn:
Margaret Eisen	$	111,620	$	115,500
Jerome Kahn, Jr.(2)	112,815		117,000
Steven N. Kaplan(2)	91,139		94,500
David C. Kleinman	118,838		123,000
Allan B. Muchin(2)	98,760		102,000
Robert E. Nason(2)	170,684		179,000
James A. Star(4)	63,439		66,000
Patricia H. Werhane(5)	50,801		92,250
John A. Wing(2)	95,115		99,000
Trustees who are interested persons of Acorn:
Charles P. McQuaid	0		0
Ralph Wanger	59,918		91,583

(1)As of December 31, 2006, the Complex consisted of 10 open end management investment company portfolios of Columbia Acorn and Wanger Advisors Trust.  In addition to the Trustee compensation fees paid by the Trust during the year ended December 31, 2006, the Trust paid $600,750 (of which $97,900 was reimbursed by Columbia Management) to Robert Scales, the Trust’s Chief Compliance Officer, Senior Vice President and General Counsel, for his services in 2006.  Mr. Scales’ “Total Compensation from the Fund Complex” was $675,000, $110,000 of which was reimbursed by Columbia Management as required by the Settlements discussed under “Legal Proceedings.”

(2)Includes fees deferred during the year pursuant to a deferred compensation plan of the Complex.  As of December 31, 2006, the values of the respective deferred compensation accounts under the plan for Messrs. Kahn, Kaplan, Muchin, Nason, Wanger and Wing were $1,015,310, $402,155, $225,300, $1,144,425, $69,665 and $540,925, respectively.

(3)The Funds do not currently provide pension or retirement plan benefits to the Trustees.

(4)Mr. Star was appointed as a Trustee on March 7, 2006.

(5)Ms. Werhane was appointed as a Trustee effective June 6, 2006.

The officers and Trustees affiliated with the Adviser serve without any compensation from the Trust.  Columbia Acorn and Wanger Advisors Trust have adopted a deferred compensation plan (the “Plan”) for the non-interested Trustees.  Under the Plan, any Trustee who is not an “interested person” of Columbia Acorn or Columbia WAM (“participating Trustees”) may defer receipt of all or a portion of their compensation as Trustees in order to defer payment of income taxes or for other reasons.  The deferred compensation payable to a participating Trustee is credited to a book reserve account as of the business day such compensation would have been paid to such Trustee.  The value of a participant’s deferral account at any time is equal to the value that the account would have had if the contributions to the account had been invested in Class Z shares of one or more of the Funds or in shares of Columbia Money Market Fund as designated by the participant.  If a participating Trustee retires, the Trustee may elect to receive payments under the plan in a lump sum or in equal annual installments over a period of five years.  If a participating Trustee dies, any amount payable under the Plan will be paid to that Trustee’s designated beneficiaries.  Each Fund’s obligation to make payments under the Plan is a general obligation of that Fund.  No Fund is liable for any other Fund’s obligations to make payments under the Plan.

Pursuant to the Settlements discussed under “Legal Proceedings,” at least 75% of the Board must meet the independence standards set forth in the Settlements (certain of those standards being more restrictive than those contained in the Investment Company Act and rules thereunder and that generally prohibit affiliations with certain Columbia and Bank of  

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America-related entities).  Those independence standards are referred to as “super-independence” standards.  The chairman of the board must meet even more stringent independence standards.  Certain other conditions in the Settlements generally require that:

·No action may be taken by the Board of Trustees (or any committee thereof) unless such action is approved by a majority of the members of the board or the committee who meet the super-independence standards.  If any action proposed to be approved by a majority of the independent trustees is not approved by the full board, the Trust is required to disclose the proposal and the vote in its shareholder report for that period;

·Beginning in 2005 and not less than every fifth calendar year thereafter, the Trust must hold a meeting of shareholders to elect trustees…; and

·The Board of Trustees must appoint either (a) a full-time senior officer who reports directly to the board with respect to his or her responsibilities, including (i) monitoring compliance with federal and state securities, applicable state laws respecting potential or actual conflicts of interest and fiduciary duties, and applicable codes of ethics and compliance manuals, (ii) managing the process by which management fees to be charged to the Funds are negotiated and (iii) preparing, or directing the preparation of, a written evaluation of, among other things, management fees charged to the Funds and to institutional and other clients, profit margins of Columbia WAM and its affiliates from supplying services to the Funds and possible economies of scale or (b) an independent compliance consultant and an independent fee consultant with similar responsibilities.……

The Agreement and Declaration of Trust (“Declaration”) provides that the Trust will indemnify its Trustees and officers against liabilities and expenses incurred in connection with litigation in which they may be involved because of their offices with the Trust but that such indemnification will not relieve any officer or Trustee of any liability to the Trust or its shareholders by reason of willful misfeasance, bad faith, gross negligence or reckless disregard of his or her duties.  The Trust, at its expense, provides liability insurance for the benefit of its Trustees and officers.

Committees       The standing committees of the Trust’s Board of Trustees are:

Committee	Members	Function	No. of Meetings Held in 2006
Executive	Charles P. McQuaid Allan B. Muchin Robert E. Nason Alternate: Ralph Wanger	Exercise powers of the Board of Trustees during intervals between meetings of the Board, with certain exceptions.	2
Audit	David C. Kleinman (chairman) Jerome Kahn, Jr. Robert E. Nason John A. Wing	Make recommendations to the Board of Trustees regarding the selection of independent auditors for the Trust, confer with the independent auditors regarding the scope and results of each audit and carry out the provisions of its charter.	4

…The Trust held a meeting of shareholders on September 27, 2005 to elect trustees.

……At a meeting of the Board of Trustees held on February 18, 2005, a majority of the trustees at that time,  other than interested persons of the Trust or the Adviser, found Promontory Financial Group LLC not unacceptable to serve as the independent compliance consultant (“ICC”) to CMD (f/k/a Columbia Funds Distributor, Inc.).  At a meeting of the Board of Trustees held on November 16, 2004, the trustees at that time unanimously voted to appoint Robert Scales as the Senior Vice President of the Trust and to designate Mr. Scales as the individual responsible for performing the duties and responsibilities of the Senior Officer as set forth in the Assurance of Discontinuance dated February 9, 2005 among the Attorney General of the State of New York, Columbia Management Advisors, Inc. and CMD, including the responsibilities of the independent fee consultant.

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Committee	Members	Function	No. of Meetings Held in 2006
Valuation	Charles P. McQuaid (chairman) Ralph Wanger Robert E. Nason Alternates: Margaret Eisen Jerome Kahn, Jr. Steven N. Kaplan David C. Kleinman Allan B. Muchin James A. Star John A. Wing Bruce H. Lauer (alternate of CWAM)	Determine valuations of portfolio securities held by any series of the Trust in instances as required by the valuation procedures adopted by the Board of Trustees.	22
Contract	Margaret Eisen (chair) Allan B. Muchin Jerome Kahn, Jr. James A. Star Patricia H. Werhane; Ex-Officio*: Robert E. Nason	Make recommendations to the Board of Trustees regarding the continuation or amendment of the investment advisory agreements between the Trust and the Adviser and other agreements with third-party service providers.	7
Governance	Allan B. Muchin (chairman) Steven N. Kaplan Robert E. Nason John A. Wing	Make recommendations to the Board of Trustees regarding committees of the board and committee assignments, make recommendations to the Board regarding the composition of the board and candidates for election as non-interested Trustees, oversee the process for evaluating the functioning of the board, and make recommendations to the board regarding the compensation of Trustees who are not affiliated with any investment adviser, administrator or distributor of the Funds.	3
Investment Performance Analysis	James A. Star (chairman) Margaret Eisen Steven N. Kaplan David Kleinman Ralph Wanger; Ex-Officio*: Charles P. McQuaid	Examine methods of mutual fund performance measurement and make recommendations to the Board of Trustees about the types of performance reports to be provided to the Board.	2
Compliance	John A. Wing (chairman) Margaret M. Eisen Steven N. Kaplan Jerome Kahn, Jr. David Kleinman Patricia H. Werhane	Provide oversight of the monitoring processes and controls regarding the Trust with legal, regulatory and internal rules, policies, procedures and standards other than those relating to accounting matters and oversight of compliance by the Trust’s investment adviser, principal underwriter and transfer agent.	9

*  Ex-Officio members are non-voting

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Although the registrant’s investment adviser, Trustees, or shareholders may submit suggested candidates for Independent Trustees to the Governance Committee, neither the Committee nor the Independent Trustees as a group shall consider those candidates on a preferential basis as opposed to other possible candidates.  Any shareholders may submit the name of a candidate for consideration by the Governance Committee by submitting the recommendation to the Trust’s Secretary. The Secretary will forward any such recommendation to the Chairman of the Governance Committee promptly upon receipt.

Investment Adviser

Columbia Wanger Asset Management, L.P. (“Columbia WAM”) (named Wanger Asset Management, L.P. prior to September 29, 2000), serves as the investment adviser for the Funds, Wanger Advisors Trust  and for other institutional accounts.  As of December 31, 2006, Columbia WAM had approximately $32.9 billion in assets under management, including the Funds.  Columbia WAM and its predecessor have managed mutual funds, including Columbia Acorn Fund since 1992.  Columbia WAM is an indirect wholly owned subsidiary of Columbia Management, which in turn is an indirect wholly owned subsidiary of Bank of America Corporation.  Prior to April 1, 2004, Columbia Management was a wholly owned subsidiary of FleetBoston Financial Corporation (“Fleet”).  On April 1, 2004, FleetBoston Financial Corporation was acquired by Bank of America Corporation.

The Portfolio Funds are managed by Columbia WAM and its affiliate Columbia Management Advisors, LLC, previously named Columbia Management Advisors, Inc. (“CMA”).  Like Columbia WAM, CMA is owned by Columbia Management.  CMA also may provide administrative and operational services to the Funds.

Each Advisory Agreement will continue from year to year so long as such continuation is approved at least annually by (1) the Board of Trustees or the vote of a majority of the outstanding voting securities of the Fund or Portfolio Fund, and (2) a majority of the Trustees who are not interested persons of any party to the Agreement, cast in person at a meeting called for the purpose of voting on such approval.  Each Advisory Agreement may be terminated at any time, without penalty, by either the Trust or Columbia WAM, upon 60 days’ written notice, and automatically terminates in the event of its assignment as defined in the 1940 Act.

A discussion of factors considered by the Board of Trustees in approving the Advisory Agreement can be found in the Trust’s annual report for the period ended December 31, 2006.

Under its Advisory Agreement for each Fund, the Adviser provides the Fund with discretionary investment services.  Specifically, the Adviser is responsible for supervising and directing the investments of the Fund in accordance with the Fund’s investment objective, program, and restrictions as provided in the Funds’ Prospectuses and this SAI.  The Adviser is also responsible for effecting all security transactions on behalf of the Fund, including the allocation of principal business and portfolio brokerage and the negotiation of commissions (see “Portfolio Transactions” below).

Under the Advisory Agreement, the Adviser is not liable for any error of judgment or mistake of law or for any loss suffered by the Funds in connection with the matters to which such Agreement relates, except a loss resulting from willful misfeasance, bad faith or gross negligence in the performance of its duties or from reckless disregard of its obligations and duties under the Agreement.

The advisory fees paid to the Adviser by each Fund for the fiscal years ended December 31, 2006, 2005 and 2004 were as follows:   

Fund	2006				2005				2004
Columbia Acorn Fund		$	115,422,000			$	94,524,000			$	79,884,000
Columbia Acorn International		28,296,000				18,872,000				14,433,000
Columbia Acorn USA		12,636,000				8,979,000				6,825,000
Columbia Acorn
Select		16,054,000				12,294,000				8,663,000
Columbia Acorn	gross	1,172,000			gross	707,000			gross	431,000
International	exp. reimb.	(1,000		)	exp. reimb.	(31,000		)	exp. reimb.	(131,000		)
Select	net	1,171,000			net	676,000			net	300,000

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Fund	2006			2005			2004
Columbia	gross	195,000		gross	205,000		gross	177,000
Thermostat Fund	exp. reimb.	(312,000	)	exp. reimb.	(300,000	)	exp. reimb.	(403,000	)
	net	(117,000	)	net	(95,000	)	net	(226,000	)

Columbia WAM receives advisory fees from some of the Portfolio Funds in which Columbia Thermostat Fund invests.

The advisory fees the Funds pay to the Adviser are calculated daily and paid monthly, at the annual rates shown below:

Average Daily Net Assets Annual Fee Rate

Columbia Acorn Fund

Up to $700 million	0.74	%
$700 million to $2 billion	0.69
$2 billion to $6 billion	0.64
$6 billion and over	0.63

Columbia Acorn International

Up to $100 million	1.19	%
$100 million to $500 million	0.94
$500 million and over	0.74

Columbia Acorn USA

Up to $200 million	0.94	%
$200 million to $500 million	0.89
$500 million to $2 billion	0.84
$2 billion to $3 billion	0.80
$3 billion and over	0.70

Columbia Acorn Select

Up to $700 million	0.85	%
$700 million to $2 billion	0.80
$2 billlion to $3 billion	0.75
$3 billion and over	0.70

Columbia Acorn International Select

All assets 0.94 %

Columbia Thermostat Fund

All assets 0.10 %

Columbia WAM has voluntarily agreed to reimburse Columbia Acorn Select (exclusive of distribution and service fees and certain other expenses) to the extent the ordinary operating expenses exceed 1.35% of the average net assets for Class Z, Class A, Class B and Class C shares.  Columbia WAM has also voluntarily agreed to reimburse Columbia Acorn International Select (exclusive of distribution and service fees, expenses associated with the Fund’s investment in other investment companies and certain other expenses) to the extent the ordinary operating expenses exceed 1.45% of the average net assets for Class Z, Class A, Class B and Class C shares.  This arrangement may be modified or terminated by either Columbia WAM or the Fund on 30 days’ notice to the other.  In addition, with respect to Columbia Thermostat Fund, Columbia WAM has contractually agreed to bear a portion of the Fund’s expenses so that the Fund’s ordinary operating expenses (exclusive of distribution and service fees and certain other expenses) do not exceed the annual  

42

rate of 0.25% of the average daily net assets through April 30, 2008 for Class Z, Class A, Class B and Class C shares.  In addition to the fees and expenses paid by Columbia Thermostat Fund directly, Columbia Thermostat Fund pays its pro rata share of the fees and expenses of the Portfolio Funds in which it invests.

Other Arrangements with Service Providers

Effective October 1, 2006, the transfer agency and shareholder servicing agreement between the Trust and CMS has been revised so that each Fund pays CMS an annual fee of $17.00 per open account, payable monthly for transfer agency services.  In addition, each Fund reimburses CMS for the sub-transfer agency fees and expenses it pays to third party dealer firms and transfer agents that maintain omnibus accounts with the Fund (“sub-transfer agency fees”), subject to a cap equal to 0.05% of the Fund’s net assets represented by the account.  Each Fund also reimburses CMS for the Fund’s allocable portion of certain reimbursable out-of-pocket expenses, which fees are approved by the Trustees from time to time, including networking account fees paid to dealer firms by CMS on shareholder accounts established or maintained pursuant to the National Securities Clearing Corporation’s (“NSCC”) networking system.   In addition, CMS also may retain as additional compensation for its services all CMS revenues for fees for wire, telephone and redemption orders, IRA trustee agent fees and account transcripts due CMS from shareholders of the Fund and interest (net of bank charges) earned with respect to the balances in accounts CMS maintains in connection with its services to the Funds.

For the period October 1, 2006 through March 31, 2007, CMS contractually agreed to waive the obligation of each Fund to pay CMS an amount equal to 50% of the sum of (1) the Excess Base/Sub-TA Amount plus (2) the amount of the Fund’s allocable share of CMS’s reimbursable out-of-pocket expenses.  The term “Excess Base/Sub-TA Amount” for a Fund equals the excess, if positive, of (1) the sum of (a) the amount payable to CMS by the Fund based on the annual $17 per account fee, plus (b) the sub-transfer agency fees, after applying the cap described above, over (2) the amount that would have been payable to CMS if the per account fee were $21 per account per annum.

Portfolio Managers

Charles McQuaid is the lead portfolio manager for Columbia Acorn Fund and Columbia Thermostat.  Robert A. Mohn is the lead portfolio manager for Columbia Acorn USA and co-portfolio manager for Columbia Acorn Fund.  P. Zachary Egan and Louis J. Mendes are the co-portfolio managers for Columbia Acorn International Fund.  Ben Andrews is lead portfolio manager for Columbia Acorn Select.  Christopher Olson is the lead portfolio manager for Columbia Acorn International Select.

Other Accounts Managed by Portfolio Managers

The portfolio managers also have responsibility for the day-to-day management of accounts other than the Funds, including separate accounts and unregistered funds.  Information regarding those other accounts is set forth below.  The advisory fees received by Columbia WAM in connection with the management of the Funds and other accounts are not based on the performance of the Funds or the other accounts.

	Number of Other Accounts Managed and Assets by  Account Type as of December 31, 2006
Portfolio Manager	Registered Investment  Companies (other than the Funds)			Other Pooled  Investment Vehicles			Other Accounts
Ben Andrews	Number:	1		Number:	0		Number:	4
	Assets:	$	175,505,000	Assets:	$	0	Assets:	$	3,000,000
P. Zachary Egan	Number:	1		Number:	0		Number:	7
	Assets:	$	221,619,000	Assets:	$	0	Assets:	$	1,700,000
Charles P. McQuaid	Number	0		Number:	2		Number:	5
	Assets:	$	0	Assets:	$	73,807,000	Assets:	$	1,434,000,000
Louis J. Mendes	Number:	2		Number:	0		Number:	12
	Assets:	$	1,710,682,000	Assets:	$	0	Assets:	$	2,800,000
Robert A. Mohn	Number:	2		Number:	1		Number:	8
	Assets:	$	1,689,789,000	Assets:	$	260,575,000	Assets:	$	1,438,978,000
Christopher Olson	Number:	2		Number:	0		Number:	4
	Assets:	$	1,542,500,000	Assets:	$	0	Assets:	$	600,000

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Compensation

As of December 31, 2006, the portfolio managers received all of their compensation from Columbia WAM  and its parent company.  Ben Andrews, P. Zachary Egan, Charles P. McQuaid, Louis J. Mendes, Robert A. Mohn, and Christopher Olson each received compensation in the form of salary and bonus.  Typically, a high proportion of an analyst’s or manager’s bonus is paid in cash with a smaller proportion going into two separate incentive plans.  The first plan is a notional investment based on the performance of certain Columbia Funds, including the Columbia Acorn Funds.  The second plan consists of Bank of America restricted stock and/or options.  Both plans vest over three years from the date of issuance.  The Columbia Wanger total bonus pool, including cash and the two incentive plans, is based on a formula, with firm wide investment performance as the primary driver.

All analysts and portfolio managers have performance benchmarks.  Analyst performance is compared to assigned industry or region stock performance within benchmark indices while portfolio manager performance is compared to entire benchmark indices. The benchmark index or indices for each Fund are (1) Columbia Acorn Fund: Russell 2500 Index, Standard & Poor’s 500 Stock Index (the “S&P 500”), and Russell 2000® Index  (the “Russell 2000”); (2) Columbia Acorn International: S&P/Citigroup EMI Global ex-U.S., the Morgan Stanley Europe, Australasia and Far East Index and the S&P/Citigroup Global ex-U.S. Cap Range $500M - $5B; (3) Columbia Acorn Select: Standard & Poor’s MidCap 400 Index; (4) Columbia Acorn USA: the Russell 2000; (5) Columbia Acorn International Select: S&P/Citigroup World ex-U.S. Cap Range $2 - 10B; and (6) Columbia Thermostat: the S&P 500 (equities), Lehman U.S. Credit Intermediate Bond Index (debt) and the Lipper Flexible Portfolio Funds Index. Performance compared to benchmark indices is the dominant performance evaluation factor for all analysts and managers.  Industry (or country) weighting recommendations are the second most important factor for analysts.  Other factors are assets managed, new analyst mentoring, teamwork, and managerial, marketing, compliance and other qualitative contributions.

Analysts and managers are positioned in a number of compensation tiers based on cumulative performance.  Excellent performance results in advancement to a higher tier each two or three years, until the highest tier is reached.  Higher tiers have higher base compensation levels and wider bonus ranges.  While cumulative performance places analysts and managers in tiers, current year performance drives changes in cash bonus levels.  Cash incentive bonuses vary by tier, and can range between a fraction of base pay to several times base pay; the objective being to provide very competitive total compensation for high performers.

In addition, Messrs. Andrews, Egan, McQuaid and Mohn each received a distribution on September 30, 2006 in connection with his association with Columbia WAM prior to its acquisition in September 2000 and Columbia WAM’s performance through September 30, 2005.  Messrs. Mendes and Olson received a distribution on September 30, 2006 from a supplemental pool for Columbia WAM employees that was established in connection with the acquisition of Columbia WAM and was based on Columbia WAM’s performance through September 30, 2005.  The final distribution each portfolio manager mentioned herein will receive is payable on September 30, 2007.

Ownership of Securities

At December 31, 2006, each portfolio manager beneficially owned (as determined pursuant to Rule 16a-1(a)(2) under the Securities Exchange Act of 1934 Act (the “1934 Act”)  shares of the respective Funds they manage having values within the indicated dollar ranges.   

	Dollar Range of Equity Securities
	in the Fund Beneficially Owned
Columbia Acorn Fund
Portfolio Managers
Charles P. McQuaid	Over $1,000,000
Robert A. Mohn	$100,001 - $500,000
Columbia Acorn International
Portfolio Managers
P. Zachary Egan	$500,001 - $1,000,000
Louis J. Mendes	$500,001 - $1,000,000
Columbia Acorn USA
Portfolio Manager
Robert A. Mohn	$100,001 - $500,000
Columbia Acorn Select
Portfolio Manager
Ben Andrews	Over $1,000,000
Columbia Acron International Select
Portfolio Manager
Christopher Olson	$500,001 - $1,000,000
Columbia Thermostat
Portfolio Manager
Charles P. McQuaid	Over $1,000,000

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Potential conflicts of interest in managing multiple accounts

Like other investment professionals with multiple clients, a portfolio manager for a Fund may face certain potential conflicts of interest in connection with managing both the Fund and other accounts at the same time.  The paragraphs below describe some of these potential conflicts that Columbia WAM believes are faced by investment professionals at most major financial firms.  Columbia WAM and the Trustees of the Funds have adopted compliance policies and procedures that attempt to address certain of these potential conflicts.

The management of accounts with different advisory fee rates and/or fee structures may raise potential conflicts of interest by creating an incentive to favor higher-fee accounts.  These potential conflicts may include, among others:

·The most attractive investments could be allocated to higher-fee accounts.

·The trading of higher-fee accounts could be favored as to timing and/or execution price.  For example, higher-fee accounts could be permitted to sell securities earlier than other accounts when a prompt sale is desirable or to buy securities at an earlier and more opportune time.

·The trading of other accounts could be used to benefit higher-fee accounts (front-running).

·The investment management team could focus their time and efforts primarily on higher-fee accounts due to a personal stake in compensation.

Potential conflicts of interest may also arise when the portfolio managers have personal investments in other accounts that may create an incentive to favor those accounts.  As a general matter and subject to limited exceptions, Columbia WAM’s investment professionals do not have the opportunity to invest in client accounts, other than the Funds.

A potential conflict of interest may arise when a Fund and other accounts purchase or sell the same securities.  On occasions when a portfolio manager considers the purchase or sale of a security to be in the best interests of a Fund as well as other accounts, Columbia WAM’s trading desk may, to the extent permitted by applicable laws and regulations, aggregate the securities to be sold or purchased in order to obtain the best execution and lower brokerage commissions, if any.  Aggregation of trades may create the potential for unfairness to the Fund or another account if one account is favored over another in allocating the securities purchased or sold — for example, by allocating a disproportionate amount of a security that is likely to increase in value to a favored account.

“Cross trades,” in which one Columbia account sells a particular security to another account (potentially saving transaction costs for both accounts), may also pose a potential conflict of interest.  Cross trades may be seen to involve a potential conflict of interest if, for example, one account is permitted to sell a security to another account at a higher price than an independent third party would pay.  Columbia WAM and the Funds’ Trustees have adopted compliance procedures that provide that any transactions between the Funds and another Columbia-advised account are to be made at an independent current market price, as required by law.

Another potential conflict of interest may arise based on the different investment objectives and strategies of the Funds and other accounts.  For example, another account may have a shorter-term investment horizon or different investment objectives, policies or restrictions than a Fund.  Depending on another account’s objectives or other factors, a portfolio manager may give advice and make decisions that may differ from advice given, or the timing or nature of decisions made, with respect to a Fund.  In addition, investment decisions are the product of many factors in addition to basic suitability for the particular account involved.  Thus, a particular security may be bought or sold for certain accounts even though it could have been bought or sold for other

45

accounts at the same time.  More rarely, a particular security may be bought for one or more accounts managed by a portfolio manager when one or more other accounts are selling the security (including short sales). There may be circumstances when purchases or sales of portfolio securities for one or more accounts may have an adverse effect on other accounts.

A Fund’s portfolio manager who is responsible for managing multiple funds and/or accounts may devote unequal time and attention to the management of those funds and/or accounts.  As a result, the portfolio manager may not be able to formulate as complete a strategy or identify equally attractive investment opportunities for each of those accounts as might be the case if he or she were to devote substantially more attention to the management of a single fund.  The effects of this potential conflict may be more pronounced where funds and/or accounts overseen by a particular portfolio manager have different investment strategies.

The Funds’ portfolio managers may be able to select or influence the selection of the brokers and dealers that are used to execute securities transactions for the Funds.  In addition to executing trades, some brokers and dealers provide portfolio managers with brokerage and research services (as those terms are defined in Section 28(e) of the Securities Exchange Act of 1934), which may result in the payment of higher brokerage fees than might have otherwise be available.  These services may be more beneficial to certain funds or accounts than to others.  Although the payment of brokerage commissions is subject to the requirement that the portfolio manager determine in good faith that the commissions are reasonable in relation to the value of the brokerage and research services provided to a Fund, a portfolio manager’s decision as to the selection of brokers and dealers could yield disproportionate costs and benefits among the Funds and/or accounts that he or she manages.

Columbia WAM or an affiliate may provide more services (such as distribution or recordkeeping) for some types of funds or accounts than for others.  In such cases, a portfolio manager may benefit, either directly or indirectly, by devoting disproportionate attention to the management of a Fund and/or accounts that provide greater overall returns to the investment manager and its affiliates.

The Funds’ portfolio managers may also face other potential conflicts of interest in managing the Funds, and the description above is not a complete description of every conflict that could be deemed to exist in managing both a Fund and other accounts.  In addition, the Funds’ portfolio managers may also manage other accounts (including their personal assets or the assets of family members) in their personal capacity.  The management of these accounts may also involve certain of the potential conflicts described above.  Investment personnel at Columbia WAM, including the Funds’ portfolio managers, are subject to restrictions on engaging in personal securities transactions pursuant to Codes of Ethics adopted by Columbia WAM and the Funds, which contain provisions and requirements designed to identify and address certain conflicts of interest between personal investment activities and the interests of the Funds.

Portfolio Transactions

Columbia WAM places the orders for the purchase and sale of portfolio securities and options and futures contracts for the Funds, subject to the oversight of the Board.  In doing so, it seeks to place purchase and sale orders in a manner that is fair and reasonable to each Fund.  Columbia WAM’s overriding objective in selecting brokers and dealers to effect portfolio transactions is to seek the best combination of net price and execution, provided that Columbia WAM may occasionally pay higher commissions to obtain research products and services as described below.  The best net price, giving effect to brokerage commissions, if any, and other transaction costs, is an important factor in this decision; however, a number of other judgmental factors may also enter into the decision.  These factors include Columbia WAM’s knowledge of negotiated commission rates currently available and other current transaction costs; the nature of the security being purchased or sold; the size of the transaction; the desired timing of the transaction; the activity existing and expected in the market for the particular security; confidentiality; the execution, clearance and settlement capabilities of the broker or dealer selected and others considered; Columbia WAM’s knowledge of the financial stability of the broker or dealer selected and such other brokers and dealers; evaluation of competing markets, including exchanges, over-the-counter markets, electronic communications networks (“ECNs”) or other alternative trading facilities; the broker’s or dealer’s responsiveness to Columbia WAM; Columbia WAM’s knowledge of actual or apparent operation problems of any broker or dealer, and the value of any research products or services provided by the broker-dealer.

Recognizing the value of those factors, Columbia WAM may cause a Fund to pay a brokerage commission in excess of what another broker may have charged for effecting the same transaction.  Columbia WAM has established internal policies for the guidance of its trading personnel, specifying minimum and maximum commissions to be paid for various types and sizes of transactions effected for the Funds.  Columbia WAM has discretion for all trades of the Funds.  Transactions which vary from the guidelines are subject to periodic supervisory review.  Those guidelines are reviewed and periodically modified, and the general level of brokerage commissions paid is periodically reviewed by Columbia WAM.  Evaluations of the reasonableness of brokerage commissions, based on the factors described in the preceding paragraph, are made by Columbia WAM’s trading

46

personnel while effecting portfolio transactions.  The general level of brokerage commissions paid is reviewed by Columbia WAM, and reports are made annually to the Board of Trustees.

Columbia WAM maintains and periodically updates a list of approved brokers and dealers that, in Columbia WAM’s judgment, are generally capable of providing best price and execution and are financially stable.  Columbia WAM’s traders are directed to use only brokers and dealers on the approved list.

Columbia WAM may place trades for the Funds through a registered broker-dealer that is an affiliate of Columbia WAM pursuant to procedures adopted by the Board of Trustees.  Such trades, for which the affiliate would receive a commission, will only be effected consistent with Columbia WAM’s obligation to seek best execution for its clients, in accordance with the Funds’ procedures adopted pursuant to Investment Company Act Rule 17e-1 governing such transactions.

It is Columbia WAM’s practice, when feasible, to aggregate for execution as a single transaction orders for the purchase or sale of a particular security, with the same terms and conditions, for the accounts of several clients in order to seek a lower commission or more advantageous net price.  All clients participating in the aggregated execution receive the same execution price and transaction costs are shared pro-rata, whenever possible.

Investment Research Products and Services Furnished by Brokers and Dealers

Columbia WAM engages in the long-standing practice in the money management industry of acquiring research and brokerage products and services (“research products”) from broker-dealer firms in return for directing trades for the Funds and other clients to those firms.  In effect, Columbia WAM is using the commission dollars paid by its clients to pay for these research products.  The money management industry uses the term “soft dollars” to refer to this industry practice.  The Board reviews Columbia WAM’s soft dollar practices on a semi-annual basis.

Columbia WAM has a duty to seek the best combination of net price and execution, provided that it may occasionally pay higher commissions to obtain research products and services as described below.  Columbia WAM faces a potential conflict of interest with this duty when it uses Client trades to obtain soft dollar products.  This conflict exists because Columbia WAM is able to use the soft dollar products in managing its client accounts without paying cash (“hard dollars”) for the product, which reduces Columbia WAM’s expenses.

The practice of using soft dollars to obtain research products and services is explicitly sanctioned by a provision of the Securities Exchange Act of 1934, (the “1934 Act”) that creates a “safe harbor” for soft dollar transactions conducted in a specified manner.  Moreover, under that provision, Columbia WAM is not required to use the soft dollar product in managing those accounts that generate the trade.  Thus, a Fund that generates the brokerage commission used to acquire a soft dollar product will not necessarily benefit directly from that product.  In effect, that Fund is cross-subsidizing Columbia WAM’s management of the other Funds and other clients that do benefit directly from the product.  Although it is inherently difficult if not impossible to document, Columbia WAM believes that over time each Fund benefits from soft dollar products such that cross subsidizations by each Fund and by other clients of Columbia WAM even out.

Columbia WAM attempts to reduce or eliminate this conflict by directing Fund trades for soft dollar products only if Columbia WAM concludes that the broker-dealer supplying the product is capable of providing a combination of the best net price and execution on the trade.  As noted above, the best net price, while significant, is one of a number of judgmental factors Columbia WAM considers in determining whether a particular broker is capable of providing the best net price and execution.  Columbia WAM may cause a Fund to pay a brokerage commission in a soft dollar trade in excess of that which another broker-dealer might have charged for the same transaction.

Columbia WAM acquires two types of soft dollar research products: (i) proprietary research created by the broker-dealer firm executing the trade and (ii) other research created by third parties that are supplied to Columbia WAM through the broker-dealer firm executing the trade.

Proprietary research consists primarily of traditional research reports, recommendations and similar materials produced by the in house research staffs of broker-dealer firms.  This research includes evaluations and recommendations of specific companies or industry groups, as well as analyses of general economic and market conditions and trends, market data, contacts and other related information and assistance.  Columbia WAM’s research analysts periodically rate the quality of proprietary research produced by various broker-dealer firms.  Based on these evaluations, Columbia WAM develops target levels of commission dollars on a firm-by-firm basis.  Columbia WAM attempts to direct trades to each such firm to meet those targets.

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Columbia WAM also uses soft dollars to acquire research created by third parties that are supplied to Columbia WAM through broker-dealers executing the trade (or other broker-dealers who “step in” to a transaction and receive a portion of the brokerage commission for the trade).

The targets that Columbia WAM establishes for various broker-dealers for both proprietary and for third party research typically reflect discussions that Columbia WAM has with the broker-dealer providing the research regarding the level of commissions it expects to receive for the research.  However, those targets, which are established on a calendar year basis, are not binding commitments, and Columbia WAM does not agree to direct a minimum amount of commissions to any broker-dealer for soft dollar research.  In setting those targets, Columbia WAM makes a determination that the value of the research is reasonably commensurate with the cost of acquiring it.  Columbia WAM will receive the research whether or not commissions directed to the applicable broker-dealer are less than, equal to or in excess of the target.  Columbia WAM generally will carry over target shortages and excesses to the next year’s target.  Columbia WAM believes that this practice reduces the conflicts of interest associated with soft dollar transactions, since Columbia WAM can meet the non-binding expectations of broker-dealers providing soft dollar research over flexible time periods.  In the case of third party research, the third party is paid by the broker-dealer and not by Columbia WAM.  Columbia WAM may enter into a contract allowing a third party vendor to use the research.

Columbia WAM also receives company-specific research for soft dollars from independent research organizations that are not brokers.

Consistent with industry practice and the safe harbor provided by the 1934 Act, Columbia WAM does not require that the Fund that generates the trade receive any benefit from the soft dollar product obtained through the trade.  As noted above, this may result in cross-subsidization of soft dollar products among various clients of Columbia WAM, including the Funds.

In certain cases, Columbia WAM will direct a trade to one broker-dealer with the instruction that it execute the trade and pay over a portion of the commission from the trade to another broker-dealer who provides Columbia WAM with a soft dollar research product or service.  The broker-dealer executing the trade “steps out” of a portion of the commission in favor of the other broker-dealer providing the soft dollar product.  Columbia WAM may engage in step out transactions in order to direct soft dollar commissions to a broker-dealer which provides research but may not be able to provide best execution.  Brokers who receive step out commissions typically are brokers providing third party soft dollar research that is not available on a hard dollars basis.  Columbia WAM has not engaged in step out transactions as a manner of compensating broker-dealers that sell shares of investment companies managed by Columbia WAM.

In certain instances, Columbia WAM pays for research products with commissions on trades executed through ECNs.  Columbia WAM may direct a portion of the commissions from these trades to an introducing broker through a Commission Sharing Agreement (“CSA”).  Where Columbia WAM has executed a CSA with an introducing broker, Columbia WAM will place a trade with the ECN, and pay the negotiated commission to the ECN.  The ECN will then credit a negotiated portion of the commission to the introducing broker as requested by Columbia WAM for the purpose of funding a pool to be used to pay for research products or services received by Columbia WAM from other third parties.  In addition, the ECN will credit a further portion of the commission negotiated by the ECN and the introducing broker to the introducing broker for its services in administrating the CSA.  The ECN makes periodic lump-sum payments to the introducing broker.  CSAs are a permitted form of soft dollar transaction under the Securities Exchange Act of 1934.  

The Trust’s purchases and sales of securities not traded on securities exchanges generally are placed by Columbia WAM with market makers for those securities on a net basis, without any brokerage commissions being paid by the Trust.  Net trading does involve, however, transaction costs.  Included in the price paid to an underwriter of portfolio securities is the spread between the price paid by the underwriter to the issuer and the price paid by the purchasers.  Each Fund’s purchases and sales of portfolio securities in the over-the-counter market usually are transacted with a broker-dealer on a net basis without any brokerage commission being paid by such Fund, but do reflect the spread between the bid and asked prices.  Columbia WAM may also transact purchases of some portfolio securities directly with the issuers.

With respect to a Fund’s purchases and sales of portfolio securities transacted with a broker or dealer on a net basis, Columbia WAM may also consider the part, if any, played by the broker or dealer in bringing the security involved to Columbia WAM’s attention, including investment research related to the security and provided to the Fund.

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Brokerage Commissions

The following table shows the total brokerage commissions paid (in thousands of dollars) by each Fund during each of the last three fiscal years:

Year	Columbia  Acorn Fund		Columbia  Acorn  International		Columbia  Acorn USA		Columbia  Acorn  Select		Columbia  Acorn  International Select		Columbia  Thermostat Fund
2006	$	15,218	$	5,859	$	1,474	$	1,971	$	282	$	0
2005	14,361		4,777		854		3,484		196		0
2004	12,154		12,154		740		1,608		150		0

The Trust is required to identify any securities of its “regular brokers or dealers” that the Funds have acquired during their most recent fiscal year.  At December 31, 2006, the Funds held securities of their regular brokers or dealers having the following values (in thousands of dollars) as set forth below:

Columbia Acorn Fund

SEI Investments Company	$	146,756
Eaton Vance Corp.	181,555
Investment Technology Group	19,296
Hong Kong Exchanges and Clearing	71,002
Nuveen Investments Inc.	111,905
Stifel Financial Corp.	5,100

Columbia Acorn International

Perpetual Trustees Australia	$	21,555
Hong Kong Exchanges and Clearing	54,617
Komercni Bank	27,245
Deutsche Boerse AG	22,070
Hiroshima Bank	13,044
Sparx Asset Management	10,361

Columbia Acorn Select

SEI Investments Company	$	44,670
Janus Capital Group Inc.	74,486
Nuveen Investments Inc.	50,583

Columbia Acorn International Select

Hong Kong Exchanges and Clearing	$	5,462
Komercni Bank	2,278
Deutsche Boerse AG	1,563

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Directed transactions include transactions on behalf of the Funds that Columbia WAM directs to a broker-dealer, through an agreement or understanding or otherwise through internal allocation procedures, because of research services provided by the  broker-dealer to the Funds.  For each broker-dealer to whom Columbia WAM directed transactions on the Funds’ behalf during the last fiscal year, the following table shows for each Fund the dollar amount (in thousands of dollars) of directed transactions, and the commissions paid on those transactions:

	Directed Transactions		Commissions
Columbia Acorn Fund	$	2,303,464	$	4,313

Columbia Acorn International                      1,356,400                    3,108

Columbia Acorn USA                          126,175                       283

Columbia Acorn Select 117,907                       205

Columbia Acorn International Select                           81,073                       151

Columbia Thermostat Fund 0 0

During the last three fiscal years, no Fund has executed any portfolio transation with any broker that was an affiliated person of Columbia WAM or CMD, or any of their affiliates.

Administration Agreement

Columbia Acorn Trust has a separate administration agreement with the Adviser under which services are provided to Columbia Acorn and each Fund by Columbia WAM.  Pursuant to the agreement, Columbia Acorn Trust shall pay Columbia WAM for its services, a fee accrued daily and paid monthly at the following annual rates:  0.05% of Columbia Acorn Trust’s average daily net assets up to $8 billion of assets; 0.04% of Columbia Acorn Trust’s average daily net assets from $8 billion to $16 billion of assets; and 0.03% of Columbia Acorn Trust’s average daily net assets over $16 billion.  Pursuant to that agreement, the Adviser provides certain administrative services to each Fund, including: (i) maintaining the books and records, including financial and corporate records, of Columbia Acorn Trust; (ii) supervising the preparation and filing of registration statements, notices, reports, tax returns and other documents; (iii) overseeing and assisting in the coordination of the performance of administrative and professional services rendered to the Funds by others; (iv) providing administrative office and data processing facilities; (v) developing and implementing procedures to monitor each Fund’s compliance with regulatory requirements and with each Fund’s investment policies and restrictions; (vi) providing for the services of employees of the Adviser who may be appointed as officers of Columbia Acorn Trust; and (vii) providing services to shareholders of the Funds.  The Administration Agreement has a one year term.  The Adviser has the power under the Administration Agreement to delegate some or all of its responsibilities to

50

others, at the Adviser’s expense.  The Adviser retains responsibility for any services it delegates.  The Adviser has delegated some or all of the services provided pursuant to the Administration Agreement to affiliates of Columbia Management.

The administrative fees paid to the Adviser by each Fund for the fiscal years ended December 31, 2006, 2005 and 2004 were as follows:

Fund	2006		2005		2004
Columbia Acorn Fund	$	7,240,000	$	6,207,000	$	5,759,000
Columbia Acorn International	1,468,000		1,005,000		838,000
Columbia Acorn USA	587,000		425,000		356,000
Columbia Acorn Select	789,000		632,000		461,000
Columbia Acorn International Select	51,000		32,000		22,000
Columbia Thermostat Fund	78,000		87,000		84,000

Principal Underwriter

CMD, One Financial Center, Boston, MA 02111, is the principal underwriter of the Funds’ shares.  CMD has no obligation to buy the Funds’ shares, and purchases the Funds’ shares only upon receipt of orders from authorized FSFs or investors.

Certain Investment Activity Limitations

The overall investment activities of Columbia WAM and its affiliates may limit the investment opportunities for the Funds in certain markets in which limitations are imposed by regulators upon the amount of investment by affiliated investors, in the aggregate or in individual issuers.  From time to time, a Fund’s activities also may be restricted because of regulatory restrictions applicable to Columbia WAM and its affiliates, and/or their internal policies.

CMD’S CHARGES AND EXPENSES

Sales Charges (dollars in thousands)

	Class A Shares Year ended December 31, 2006
	Columbia  Acorn Fund			Columbia  Acorn  International			Columbia  Acorn USA		Columbia  Acorn Select		Columbia  Acorn  International Select		Columbia  Thermostat Fund
Aggregate initial sales charges on Fund share sales	$	4,121		$	1,264		$	352	$	728	$	111	$	150
Initial sales charges retained by CMD	$	718,609		$	196,048		$	59,372	$	125,930	$	17,572	$	24,815
Aggregate contingent deferred sales charges (CDSC) on Fund redemptions retained by CMD	$	(18,718	)	$	(10,270	)	$	370	$	781	$	30	$	0

	Class B Shares Year ended December 31, 2006
	Columbia  Acorn Fund		Columbia  Acorn  International		Columbia  Acorn USA		Columbia  Acorn Select		Columbia  Acorn  International  Select		Columbia  Thermostat Fund
Aggregate CDSC on Fund redemptions retained by CMD	$	1,763,979	$	128,451	$	104,380	$	313,795	$	12,647	$	217,597

51

	Class C Shares Year ended December 31, 2006
	Columbia  Acorn Fund		Columbia  Acorn  International		Columbia  Acorn USA		Columbia Acorn Select		Columbia  Acorn  International Select		Columbia  Thermostat Fund
Aggregate CDSC on Fund redemptions retained by CMD	$	89,071	$	23,266	$	5,871	$	14,907	$	784	$	5,976

	Class A Shares Year ended December 31, 2005
	Columbia  Acorn Fund		Columbia  Acorn  International		Columbia  Acorn USA		Columbia  Acorn Select			Columbia  Acorn  International Select		Columbia  Thermostat Fund
Aggregate initial sales charges on Fund share sales	$	4,777	$	716	$	315	$	1,808		$	67	$	398
Initial sales charges retained by CMD	$	812,402	$	115,750	$	51,780	$	271,751		$	10,833	$	61,262
Aggregate contingent deferred sales charges (CDSC) on Fund redemptions retained by CMD	$	1,941	$	3	$	0	$	(1,829	)	$	1	$	5

	Class B Shares Year ended December 31, 2005
	Columbia  Acorn Fund		Columbia  Acorn  International		Columbia  Acorn USA		Columbia  Acorn Select		Columbia  Acorn  International Select		Columbia  Thermostat Fund
Aggregate CDSC on Fund redemptions retained by CMD	$	2,147,740	$	92,069	$	122,138	$	375,163	$	12,539	$	162,027

	Class C Shares Year ended December 31, 2005
	Columbia  Acorn Fund		Columbia  Acorn  International		Columbia  Acorn USA		Columbia  Acorn Select		Columbia  Acorn  International Select		Columbia  Thermostat Fund
Aggregate CDSC on Fund redemptions retained by CMD	$	58,070	$	5,462	$	1,160	$	22,676	$	1,193	$	7,903

	Class A Shares Year ended December 31, 2004
	Columbia  Acorn Fund		Columbia  Acorn  International		Columbia  Acorn USA		Columbia  Acorn Select		Columbia  Acorn  International Select		Columbia  Thermostat Fund
Aggregate initial sales charges on Fund share sales	$	4,239	$	366	$	173	$	2,433	$	30	$	1,084
Initial sales charges retained by CMD	$	688,302	$	57,154	$	27,933	$	369,071	$	6,127	$	169,202
Aggregate contingent deferred sales charges (CDSC) on Fund redemptions retained by CMD	$	19,547	$	120	$	827	$	11,665	$	0	$	9

	Class B Shares Year ended December 31, 2004
	Columbia  Acorn Fund		Columbia  Acorn  International		Columbia  Acorn USA		Columbia  Acorn Select		Columbia  Acorn  International Select		Columbia  Thermostat Fund
Aggregate CDSC on Fund redemptions retained by CMD	$	2,139,741	$	83,937	$	148,011	$	329,294	$	11,410	$	164,282

52

	Class C Shares Year ended December 31, 2004
	Columbia  Acorn Fund		Columbia  Acorn  International		Columbia  Acorn USA		Columbia  Acorn Select		Columbia  Acorn  International Select		Columbia  Thermostat Fund
Aggregate CDSC on Fund redemptions retained by CMD	$	134,065	$	5,500	$	8,238	$	37,178	$	84	$	14,900

Ownership of the Fund

As of April 1, 2006, the following shareholders of record owned 5% or more of each class of the outstanding shares of any Fund:

		Percentage of
		Outstanding
Name and Address	Fund	Shares Held
Charles Schwab & Co. Inc.(1)	Columbia Acorn Fund Z	12.58
101 Montgomery Street	Columbia Acorn International Z	9.91
San Francisco, CA 94104-4122	Columbia Acorn USA Z	6.40
	Columbia Acorn Select Z	10.21
	Columbia Acorn International Select Z	8.35
State of Illinois Employees	Columbia Acorn Fund Z	8.10
Deferred Compensation Plan(2)
PO Box 19208
Springfield, IL 62794-9208
Fidelity Investments	Columbia Acorn Fund Z	6.64
100 Magellan Way #KW1C	Columbia Acorn USA Z	31.93
Covington, KY 41015-1999	Columbia Acorn Select Z	18.12
Bank of New York	Columbia Acorn USA Z	7.96
FBO New York State Deferred
Compensation Plan
1 Wall St., Floor 12
New York, NY 10286-001
Vanguard Fiduciary Trust Co.(1)	Columbia Acorn USA Z	6.03
PO Box 2600
Valley Forge, PA 19482-2600
Bank of America NA.(1)	Columbia Acorn Fund Z	7.84
411 N. Akard St.	Columbia Acorn International Z	25.61
Dallas, TX 75201-3307	Columbia Acorn USA Z	5.95
	Columbia Acorn Select Z	26.05
	Columbia Acorn International Select Z	52.63
Ralph Wanger	Columbia Thermostat Fund Z	5.28
191 North Wacker, Suite 1500
Chicago, IL 60606
Columbia Management Advisors Inc.	Columbia Thermostat Fund Z	22.46
245 Summer St.
FL 3 MS:MADE 11603H
Boston, MA 02210-1129

53

		Percentage of
		Outstanding
Name and Address	Fund	Shares Held
LaSalle Bank National	Columbia Thermostat Fund Z	6.02
Association.(1)
PO Box 1443
Chicago, IL 60690-1443
Charles Schwab & Co. Inc.(1)	Columbia Acorn Fund A	16.46
101 Montgomery Street	Columbia Acorn International A	24.97
San Francisco, CA 94104-4122	Columbia Acorn USA A	12.16
	Columbia Acorn Select A	25.20
	Columbia Acorn International Select A	28.43
Merrill Lynch Pierce Fenner & Smith(1)	Columbia Acorn Fund A	5.63
4800 Deer Lake Drive	Columbia Acorn USA A	13.83
Jacksonville, FL 32246-6484	Columbia Acorn International Select A	6.23
Citigroup Global Markets, Inc. (1)	Columbia Acorn Fund B	7.8
333 W. 34th Street	Columbia Acorn International B	8.28
New York, NY 10001-2402	Columbia Acorn USA B	9.33
	Columbia Acorn Select B	5.90
	Columbia Acorn International Select B	5.56
Citigroup Global Markets, Inc. (1)	Columbia Acorn Fund C	16.33
333 W. 34th Street	Columbia Acorn International C	10.21
New York, NY 10001-2402	Columbia Acorn USA C	9.27
	Columbia Acorn Select C	13.62
	Columbia Acorn International Select C	8.40
	Columbia Thermostat C	8.15
Merrill Lynch Pierce Fenner &	Columbia Acorn Fund C	16.61
Smith(1)	Columbia Acorn International C	8.79
4800 Deer Lake Drive	Columbia Acorn USA C	10.17
Jacksonville, FL 32246-6484	Columbia Acorn Select C	15.53
	Columbia Acorn International Select C	10.03
	Columbia Thermostat C	5.47

(1)   Shares are held of record on behalf of customers, and not beneficially.

(2)   Shares are held of record on behalf of plan participants, and not beneficially.

At April 1, 2007, the Trustees and officers of the Trust as a group owned beneficially less than 1% of the outstanding shares of each Fund.  As of April 1, 2007, none of the independent Trustees owns beneficially or of record any shares of Columbia WAM or CMD, or of any person directly or indirectly controlling, controlled by, or under common control with Columbia WAM or CMD.

The following table shows the dollar range of equity securities “beneficially” owned (within the meaning of that term as defined in rule 16a-1(a)(2) under the 1934 Act) by each Trustee as of December 31, 2006 (i) in the Funds and (ii) in the funds in the Columbia Funds Complex.

54

			Aggregate Dollar Range of
			Equity Securities in All
			Registered Investment
		Dollar Range of Equity	Companies Overseen by
		Securities Owned	Trustee in
Name of Trustee	Name of Fund	in each Fund	Columbia Funds Complex
Trustees who are not interested persons of Columbia Acorn:
Margaret Eisen	Columbia Acorn Fund	None	Over $100,000
	Columbia Acorn International	Over $100,000
	Columbia Acorn USA	None
	Columbia Acorn Select	None
	Columbia Acorn International Select	None
	Columbia Thermostat Fund	None
Jerome Kahn, Jr.*	Columbia Acorn Fund	Over $100,000	Over $100,000
	Columbia Acorn International	None
	Columbia Acorn USA	Over $100,000
	Columbia Acorn Select	None
	Columbia Acorn International Select	Over $100,000
	Columbia Thermostat Fund	None
Steven N. Kaplan*	Columbia Acorn Fund	$10,001-50,000	$10,001-50,000
	Columbia Acorn International	$10,001-50,000
	Columbia Acorn USA	None
	Columbia Acorn Select	$1-10,000
	Columbia Acorn International Select	None
	Columbia Thermostat Fund	None
David C. Kleinman	Columbia Acorn Fund	$10,001-50,000	Over $100,000
	Columbia Acorn International	$50,001-100,000
	Columbia Acorn USA	$10,001-50,000
	Columbia Acorn Select	$10,000-50,000
	Columbia Acorn International Select	$1-10,000
	Columbia Thermostat Fund	None
Allan B. Muchin*	Columbia Acorn Fund	$10,001-50,000	Over $100,000
	Columbia Acorn International	Over $100,000
	Columbia Acorn USA	$10,001-50,000
	Columbia Acorn Select	$10,001-50,000
	Columbia Acorn International Select	$10,001-50,000
	Columbia Thermostat Fund	None
Robert E. Nason*	Columbia Acorn Fund	$50,001-100,000	Over $100,000
	Columbia Acorn International	$50,001-100,000
	Columbia Acorn USA	$10,001-50,000
	Columbia Acorn Select	$10,001-50,000
	Columbia Acorn International Select	$1-10,000
	Columbia Thermostat Fund	$10,001-50,000

55

			Aggregate Dollar Range of
			Equity Securities in All
			Registered Investment
		Dollar Range of Equity	Companies Overseen by
		Securities Owned	Trustee in
Name of Trustee	Name of Fund	in each Fund	Columbia Funds Complex
James A. Star	Columbia Acorn Fund	$50,001-100,000	Over $100,000
	Columbia Acorn International	$50,001-100,000
	Columbia Acorn USA	$10,001-50,000
	Columbia Acorn Select	Over $100,000
	Columbia Acorn International Select	None
	Columbia Thermostat Fund	None
John A. Wing*	Columbia Acorn Fund	Over $100,000	Over $100,000
	Columbia Acorn International	Over $100,000
	Columbia Acorn USA	Over $100,000
	Columbia Acorn Select	None
	Columbia Acorn International Select	None
	Columbia Thermostat Fund	None

*In addition to the value of the shares owned as set forth above, Messrs. Kahn, Kaplan, Muchin, Nason and Wing have deferred trustee fees pursuant to a deferred compensation plan described above.  The value of the deferred fees is determined as if the fees had been invested in shares of one or more Funds, as determined by the Trustee, as of the date of the deferral.  As of December 31, 2006, the value of each of the deferred compensation accounts in the Funds for Messrs. Kahn, Kaplan, Muchin, Nason, Wanger and Wing was $1,015,310, $402,155, $225,300, $1,144,425, $69,665 and $540,925, respectively.

			Aggregate Dollar Range of
			Equity Securities in All
			Registered Investment
		Dollar Range of Equity	Companies Overseen by
		Securities Owned	Trustee in
Name of Trustee	Name of Fund	in each Fund	Columbia Funds Complex
Trustees who are interested persons of Columbia Acorn:
Charles P. McQuaid	Columbia Acorn Fund	Over $100,000	Over $100,000
	Columbia Acorn International	Over $100,000
	Columbia Acorn USA	Over $100,000
	Columbia Acorn Select	Over $100,000
	Columbia Acorn International Select	Over $100,000
	Columbia Thermostat Fund	Over $100,000
Ralph Wanger	Columbia Acorn Fund	Over $100,000	Over $100,000
	Columbia Acorn International	Over $100,000
	Columbia Acorn USA	Over $100,000
	Columbia Acorn Select	Over $100,000
	Columbia Acorn International Select	Over $100,000
	Columbia Thermostat Fund	Over $100,000

56

12b-1 Plan, Contingent Deferred Sales Charges and Conversion of Shares

Each Fund offers four classes of shares - Class Z, Class A, Class B, and Class C.  Each Fund may in the future offer other classes of shares.  The Trustees have approved a 12b-1 Plan (Plan) pursuant to Rule 12b-1 under the 1940 Act for each class except Class Z.  Under the Plan, each Fund pays CMD monthly service and distribution fees at the annual rates described in the Prospectus for that Funds’ Class A, Class B and Class C shares.  CMD may use the entire amount of such fees to defray the costs of commissions and service fees paid to FSFs and for certain other purposes.  Since the distribution and service fees are payable regardless of CMD’s expenses, CMD may realize a profit from the fees.

The Plan authorizes any other payments by the Funds to CMD and its affiliates (including the Adviser) with respect to the Class A, B and C shares to the extent that such payments might be construed to be indirect financing of the distribution of those shares.

The Trustees believe the Plan could be a significant factor in the growth and retention of Fund assets resulting in a more advantageous expense ratio and increased investment flexibility which could benefit each class of Fund shareholders.  The Plan will continue in effect from year to year so long as its continuance is specifically approved at least annually by a vote of the Trustees, including the Trustees who are not interested persons of the Trust (Independent Trustees) and have no direct or indirect financial interest in the operation of the Plan or in any agreements related to the Plan, cast in person at a meeting called for the purpose of voting on the Plan.  The Plan may not be amended to increase the fee materially without approval by vote of a majority of the outstanding voting securities of the relevant class of shares and all material amendments of the Plan must be approved by the Trustees in the manner provided in the foregoing sentence.  The Plan may be terminated at any time by vote of a majority of the Independent Trustees or by vote of a majority of the outstanding voting securities of the relevant class of shares.  The continuance of the Plan will only be effective if the selection and nomination of the Trustees who are not interested persons of the Trust is effected by such Independent Trustees.

Class A shares are offered at net asset value plus varying sales charges.  Class B shares are offered at net asset value and are subject to a CDSC if redeemed within six years after purchase.  Class C shares are offered at net asset value and are subject to a 1.00% CDSC on redemptions within one year after purchase.  The CDSCs are described in the Prospectus.  Class Z shares are offered at net asset value and are not subject to a CDSC.  However, generally, if you redeem or exchange Class A, B, C or Z shares of Columbia Acorn International or Columbia Acorn International Select that you have owned 60 days or less, that Fund will charge you a redemption fee of 2% of the redemption proceeds.  See “How to Sell Shares” for more information on redemption fees.  The CDSCs and initial sales charge are described in the Prospectuses for the Funds’ Class A, Class B and Class C shares.

No CDSC will be imposed on shares derived from reinvestment of distributions or amounts representing capital appreciation.  In determining the applicability and rate of any CDSC, it will be assumed that a redemption is made first of shares representing capital appreciation, next of shares representing reinvestment of distributions and finally of other shares held by the shareholder for the longest period of time.

A certain number of years, depending on the program you purchased your shares under, after the end of the month in which a Class B share is purchased, such share and a pro rata portion of any shares issued on the reinvestment of distributions will be automatically converted into Class A shares, which are not subject to the distribution fee, having an equal value.  Class C shares do not convert.  See the Prospectus for a description of the different programs.

Redemption Fees (dollars in thousands)

	Class Z Shares
	Year ended December 31, 2006
	Columbia Acorn International	Columbia Acorn International Select
Contingent redemption fees charged on Fund share redemptions retained by the Fund	$  147	$  9

	Class Z Shares
	Year ended December 31, 2005
	Columbia Acorn International	Columbia Acorn International Select
Contingent redemption fees charged on Fund share redemptions retained by the Fund	$  65	$  9

57

12b-1 Fees Paid to CMD in 2006 (dollars in thousands)

Columbia Acorn Fund	$	34,110
Columbia Acorn International	$	1,998
Columbia Acorn USA	$	1,604
Columbia Acorn International Select	$	153
Columbia Acorn Select	$	5,282
Columbia Thermostat Fund	$	1,043

Sales-related expenses (dollars in thousands) of CMD relating to the Class A, B and C shares of the Funds for the fiscal year ended December 31, 2006 were:

Columbia Acorn Fund

	Year ended December 31, 2006
	Class A Shares		Class B Shares		Class C Shares
Fees to FSFs	$	12,587,189	$	4,186,959	$	4,742,680
Cost of sales material relating to the Fund (including printing and mailing expenses)	$	290,722	$	40,835	$	59,164
Allocated travel, entertainment and other promotional expenses (including advertising)	$	1,470,364	$	206,530	$	299,231

Columbia Acorn USA

	Year ended December 31, 2006
	Class A Shares		Class B Shares		Class C Shares
Fees to FSFs	$	819,850	$	197,589	$	294,444
Cost of sales material relating to the Fund (including printing and mailing expenses)	$	24,976	$	1,341	$	4,215
Allocated travel, entertainment and other promotional expenses (including advertising)	$	126,321	$	6,783	$	21,317

Columbia Acorn Select

	Year ended December 31, 2006
	Class A Shares		Class B Shares		Class C Shares
Fees to FSFs	$	2,672,935	$	639,036	$	574,773
Cost of sales material relating to the Fund (including printing and mailing expenses)	$	50,720	$	4,703	$	6,276
Allocated travel, entertainment and other promotional expenses (including advertising)	$	256,525	$	23,785	$	31,740

Columbia Acorn International

	Year ended December 31, 2006
	Class A Shares		Class B Shares		Class C Shares
Fees to FSFs	$	680,331	$	519,106	$	654,693
Cost of sales material relating to the Fund  (including printing and mailing expenses)	$	42,829	$	6,574	$	12,441
Allocated travel, entertainment and other  promotional expenses (including advertising)	$	216,613	$	33,248	$	62,922

Columbia Acorn International Select

	Year ended December 31, 2006
	Class A Shares		Class B Shares		Class C Shares
Fees to FSFs	$	37,385	$	51,012	$	32,912
Cost of sales material relating to the Fund  (including printing and mailing expenses)	$	2,356	$	621	$	571
Allocated travel, entertainment and other  promotional expenses (including advertising)	$	11,914	$	3,139	$	2,886

58

Columbia Thermostat Fund

	Year ended December 31, 2006
	Class A Shares		Class B Shares		Class C Shares
Fees to FSFs	$	162,254	$	272,665	$	102,545
Cost of sales material relating to the Fund  (including printing and mailing expenses)	$	2,847	$	2,710	$	1,533
Allocated travel, entertainment and other  promotional expenses (including advertising)	$	14,400	$	13,740	$	7,756

LEGAL PROCEEDINGS

The discussion below supplements the information included in the Prospectuses under the heading “Managing the Fund — Legal Proceedings.”

On February 9, 2005, Columbia Management Advisors, Inc. (which has since merged into Banc of America Capital Management, LLC (now named Columbia Management Advisors, LLC)) (CMA) and Columbia Funds Distributor, Inc. (which has been renamed Columbia Management Distributors, Inc.) (CMD) (collectively, the Columbia Group) entered into an Assurance of Discontinuance with the New York Attorney General (NYAG) (the NYAG Settlement) and consented to the entry of a cease-and-desist order by the SEC (the SEC Order) on matters relating to mutual fund trading.  The SEC Order and the NYAG Settlement are referred to collectively as the “Settlements.”  CWAM, the adviser to the Wanger Advisors Funds and the Columbia Acorn Funds, was not a respondent in either proceeding nor were any of its officers or affiliates.  Although none of the Columbia Acorn Funds is a party to the Settlements and in order for CMA to continue to provide administrative services to the Columbia Acorn Funds, the Board of Trustees of the Columbia Acorn Trust agreed to conform to certain governance requirements, including the election of an independent board chair.

Under the terms of the SEC Order, the Columbia Group agreed, among other things, to:  pay $70 million in disgorgement and $70 million in civil money penalties; cease and desist from violations of the antifraud provisions and certain other provisions of the federal securities laws; maintain certain compliance and ethics oversight structures; retain an independent consultant to review the Columbia Group’s applicable supervisory, compliance, control and other policies and procedures; and retain an independent distribution consultant (see below).  The NYAG Settlement also, among other things, requires Columbia and its affiliates to reduce management fees for certain of the funds in the Columbia, Columbia Acorn Trust and Wanger Advisors Trust family of mutual funds (including the former National Funds) and other mutual funds collectively by $32 million per year for five years, for a projected total of $160 million in management fee reductions.

Pursuant to the procedures set forth in the SEC Order, the $140 million settlement amounts described above will be distributed in accordance with a distribution plan that was developed by an independent distribution consultant and approved by the SEC on April 6, 2007.

As a result of these matters or any adverse publicity or other developments resulting from them, there may be increased redemptions or reduced sales of fund shares, which could increase transaction costs or operating expenses, or have other adverse consequences for the funds.

A copy of the SEC Order is available on the SEC website at http://www.sec.gov.  A copy of the NYAG Settlement is available as part of the Bank of America Corporation Form 8-K filing on February 10, 2005.

CODE OF ETHICS

The 1940 Act and rules thereunder require that the Trust and the Adviser establish standards and procedures for the detection and prevention of certain conflicts of interest, including activities by which persons having knowledge of the investments and investment intentions of the Funds might take advantage of that knowledge for their own benefit.  The Trust, the Adviser and CMD have adopted Codes of Ethics pursuant to the 1940 Act.  These Codes of Ethics permit personnel subject to the Codes to invest in securities, including securities that may be purchased or held by the Funds under limited circumstances.  These Codes of Ethics can be reviewed and copied at the SEC’s Public Reference Room and may be obtained by calling the SEC at 1-202-942-8090.  These Codes are also available on the EDGAR Database on the SEC’s internet web site at http://www.sec.gov, and may also be obtained, after paying a duplicating fee, by electronic request to publicinfo@sec.gov or by writing to the SEC’s Public Reference Section, Washington, D.C. 20549-0102.

59

ANTI-MONEY LAUNDERING COMPLIANCE

The Funds are required to comply with various anti-money laundering laws and regulations.  Consequently, the Funds may request additional information from you to verify your identity.  If at any time the Funds believe a shareholder may be involved in suspicious activity or if certain account information matches information on government lists of suspicious persons, the Funds may choose not to establish a new account or may be required to “freeze” a shareholder’s account.  The Funds also may be required to provide a governmental agency with information about transactions that have occurred in a shareholder’s account or to transfer monies received to establish a new account, transfer an existing account or transfer the proceeds of an existing account to a governmental agency.  In some circumstances, the law may not permit a Fund to inform the shareholder that it has taken th e actions described above.

PROXY VOTING POLICIES AND FUND PROXY VOTING RECORD

The Funds have delegated to Columbia WAM the responsibility to vote proxies relating to portfolio securities held by the Funds.  In deciding to delegate this responsibility to Columbia WAM, the Board of Trustees of the Trust reviewed and approved the policies and procedures adopted by Columbia WAM.  These included the procedures that Columbia WAM follows when a vote presents a conflict between the interests of the Funds and their shareholders and Columbia WAM, its affiliates, its other clients or other persons.

Columbia WAM’s policy is to vote all proxies for Fund securities in a manner considered by Columbia WAM to be in the best interest of the Funds and their shareholders without regard to any benefit to Columbia WAM, its affiliates, its other clients or other persons.  Columbia WAM examines each proposal and votes against the proposal, if, in its judgment, approval or adoption of the proposal would be expected to impact adversely the current or potential market value of the issuer’s securities.  Columbia WAM also examines each proposal and votes the proxies against the proposal, if, in its judgment, the proposal would be expected to affect adversely the best interest of the Funds.  Columbia WAM determines the best interest of the Funds in light of the potential economic return on the Funds’ investment.

Columbia WAM addresses potential material conflicts of interest by having predetermined voting guidelines and by having each individual stock analyst review and vote each proxy for the stocks that he or she follows.  For those proposals that require special consideration or in instances where special circumstances may require varying from the predetermined guideline, Columbia WAM’s Proxy Committee determines the vote in the best interest of the Funds, without consideration of any benefit to Columbia WAM, its affiliates, its other clients or other persons.  Columbia WAM’s Proxy Committee is composed of representatives of Columbia WAM’s equity investments, equity research, compliance, legal and administration functions.  In addition to the responsibilities described above, the Proxy Committee has the responsibility to review, on an annual basis, Columbia WAM’s proxy voting policies to ensure consistency with internal and regulatory agency policies, and to develop additional predetermined voting guidelines to assist in the review of proxy proposals.

The Proxy Committee may vary from a predetermined guideline if it determines that voting on the proposal according to the predetermined guideline would be expected to impact adversely the current or potential market value of the issuer’s securities or to affect adversely the best interest of the client.  References to the best interest of a client refer to the interest of the client in terms of the potential economic return on the client’s investment.  In determining the vote on any proposal, the Proxy Committee does not consider any benefit other than benefits to the owner of the securities to be voted.  A member of the Proxy Committee is prohibited from voting on any proposal for which he or she has a conflict of interest by reason of a direct relationship with the issuer or other party affected by a given proposal.  Persons making recommendations to the Proxy Committee or its members are required to disclose to the Committee any relationship with a party making a proposal or other matter known to the person that would create a potential conflict of interest.

Columbia WAM has retained Institutional Shareholder Services (“ISS”), a third party vendor, to implement its proxy voting process.  ISS provides proxy analysis, record keeping services, vote disclosure services and independent proxy voting services.

Columbia WAM’s proxy voting policies, guidelines and procedures are included in this SAI as Appendix II.  In accordance with SEC regulations, the Trust’s proxy voting record for the most recent twelve-month period ended June 30 has been filed with the SEC.  You may obtain a copy of the Funds’ proxy voting record (i) on the SEC’s website at www.sec.gov; (ii) on the Columbia Management website at www.columbiamanagement.com, and (ii) without charge, upon request by calling (800) 426-3750.

DISCLOSURE OF FUND INFORMATION

The Trustees of Columbia Acorn Trust have adopted policies and procedures with respect to the disclosure of the Funds’ portfolio holdings and trading strategies by the Funds, Columbia WAM, Columbia Management and their affiliates (the  

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“Policies”).  The Policies are designed to prevent any disclosure of confidential Fund portfolio holdings information that could harm the Funds and their shareholders.  The Policies provide that Fund portfolio holdings information generally may not be disclosed to any party prior to public disclosure which is: (1) the business day next following the posting of such information on Columbia Management’s website at www.columbiafunds.com; or (2) the time a Fund discloses the information in a publicly available SEC filing required to include such information.  As described below, the Policies provide for certain limited exceptions that allow for disclosure of Fund portfolio holdings information in advance of public dissemination only when a Fund has legitimate business purposes for doing so and the recipients are subject to a duty of confidentiality, including a duty not to trade on the nonpublic information.  The Policies prohibit Columbia Management, Columbia WAM and the Funds’ other service providers from entering into any agreement to disclose Fund portfolio holdings information or trading strategies in violation of the Policies or from entering into any agreement to disclose portfolio information in exchange for any form of consideration.  The Policies incorporate and adopt the supervisory controls and recordkeeping requirements established in Columbia WAM’s Policies.  Columbia WAM has also adopted policies and procedures to monitor for compliance with the Policies.

Public Disclosures

The Funds’ portfolio holdings are currently disclosed to the public through required filings with the SEC and on Columbia Management’s website at www.columbiafunds.com.  Full portfolio holdings information as of a month-end is posted monthly approximately 30-40 calendar days after such month-end.  In addition, the Funds’ top 15 month-end portfolio holdings and the number of shares held or percentage of Fund assets represented by those shares are made publicly available at www.columbiafunds.com on or about 15 calendar days following such month-end.  The scope of the information pursuant to the Policies relating to each Fund’s portfolio that is made available on Columbia Management’s website may change from time to time without prior notice.

The Funds file their portfolio holdings with the SEC for each fiscal quarter on either Form N-CSR (with respect to each annual period and semiannual period) or Form N-Q (with respect to the first and third quarters of the Funds’ fiscal year).  Shareholders may obtain the Funds’ Forms N-CSR and N-Q filings on the SEC’s website at www.sec.gov, a link to which is provided on Columbia Management’s website.  In addition, the Funds’ Forms N-CSR and N-Q filings may be reviewed and copied at the SEC’s public reference room in Washington, D.C.  You may call the SEC at 1-800-SEC-0330 for information about the SEC’s website or the operation of the public reference room.

A Fund, Columbia Management, Columbia WAM or their affiliates may include portfolio holdings information that has already been made public through a web posting or SEC filing in marketing literature and other communications to shareholders, advisers or other parties.  In addition, certain advisory clients of Columbia WAM that follow a strategy similar to that of a Fund have access to their own custodial account’s portfolio holdings information before such Fund posts its holdings to Columbia Management’s website.  It is possible that when clients observe transactions in their own accounts, they may infer transactions of the Funds prior to public disclosure of Fund transactions.

Other Disclosures

Pursuant to the Policies, the Funds may selectively disclose their portfolio holdings information in advance of public disclosure on a confidential basis to various Fund service providers that require such information for the legitimate business purpose of assisting the Funds with day-to-day business affairs.  Neither the Funds nor Columbia Management, Columbia WAM and their affiliates receive compensation or consideration from the service providers for the portfolio holdings information.  In addition to Columbia Management, Columbia WAM and their affiliates, these service providers are listed below:

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IDENTITY OF RECIPIENT	PURPOSE OF DISCLOSURE	FREQUENCY OF DISCLOSURE
Wilshire Associates	Supports performance analysis software.	Daily
Plexus	Provides best execution data.	Quarterly
State Street Bank and Trust Company	Funds’ custodian; receives trade files containing information for the Funds.	Daily
Sikich ICS	Host of the Funds’ trustee website.	Monthly
GIS Ltd. (MFACT)	Provides support for Columbia WAM’s accounting systems.	Information sent on an “as needed basis,” which is generally less than twice per year
Macgregor	Provides support for Columbia WAM’s trading system.	1 – 2 times per year
Data Communique	Automates marketing materials and populates data in fact sheet templates. Fact sheets will be distributed to investment professionals and clients only after the information is deemed public under the Policies.	Monthly/ Quarterly
Factset Data Systems, Inc.	Provides quantitative analytics, charting and fundamental data to investment, marketing, performance and distribution personnel.	Daily
Merrill Corporation	Printer for the Funds’ prospectuses, SAIs, supplements and sales materials.	Quarterly
Bowne & Co., Inc.	Printer for the Funds’ prospectuses, SAIs, supplements and sales materials.	Quarterly
Institutional Shareholder Services, Inc. (“ISS”)	Proxy service provider to the Funds. Holdings are only redistributed by ISS through voting the shares held and within the Funds’ N-PX filings.	Daily
Bell, Boyd & Lloyd LLP	Legal counsel to the Funds and the independent trustees.	As needed
PricewaterhouseCoopers	Funds’ independent registered public accounting firm, providing audit services, tax return review services, and assistance and consultation in connection with the review of various SEC filings.	As needed

Pursuant to agreements in such form as the Chief Compliance Officer (“CCO”) may require, these service providers are required to keep such information confidential, and are prohibited from trading based on the information or otherwise using the information except as necessary in providing services to the Funds.

The Funds have authorized Columbia WAM’s President (and his designated subordinates) to make appropriate disclosures of the Funds’ holdings to certain Columbia Management affiliates, to provide the Funds’ custodian, subcustodians and pricing service with daily trade information and to disclose necessary portfolio information to the Funds’ proxy service. The Funds have also authorized Columbia WAM’s President and Chief Operating Officer (and their designated subordinates) to disclose portfolio information to independent auditors in connection with audit procedures.  In addition, the Funds have authorized Columbia Management Advisors, LLC (“CMA”) and Columbia WAM’s President (and his designated subordinates) to disclose necessary information to printing firms engaged by CMA to prepare periodic reports to Fund shareholders.

Columbia WAM uses a variety of broker-dealers and other agents to effect securities transactions on behalf of the Funds.  These broker-dealers become aware of the Funds’ intentions, transactions and positions, in performing their functions.  Further, the Funds’ ability to identify and execute transactions in securities is dependent, in part, on information provided to Columbia WAM by broker-dealers who are market makers in certain securities or otherwise have the ability to assist the Funds in executing their orders.  To facilitate that process, the Trustees have authorized Columbia WAM’s President and Managing Director of Trading (and their designated subordinates) to disclose portfolio information or anticipated transactions to broker-dealers who may execute Fund transactions.  This disclosure is limited to that information necessary to effect the Funds’ securities transactions and assist Columbia WAM in seeking to obtain best execution.

The CCO is responsible for implementation of the Policies.  The CCO is required to report to the Trustees any violations of the Policies that come to his attention and may approve non-public disclosures of a Fund’s portfolio holdings; provided that, such disclosure is consistent with the Policies, including whether the disclosure furthers a legitimate business purpose of such Fund and is therefore in the best interests of that Fund’s shareholders and that such approvals are reported to the Trustees.

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CUSTODIAN

State Street Bank and Trust Company, located at 2 Avenue De Lafayette, Boston, MA 02111-2900 (“State Street”) is the custodian of the assets of the Funds.  The Custodian is responsible for holding all securities and cash of the Funds, receiving and paying for securities purchased, delivering against payment securities sold, receiving and collecting income from investments, making all payments covering expenses of the Funds, and performing other administrative duties, all as directed by authorized persons of the Funds.  Columbia WAM and Columbia Management supervise State Street in such matters as purchase and sale of portfolio securities, payment of dividends or payment of expenses of the Funds.  Portfolio securities purchased in the U.S. are maintained in the custody of State Street or other domestic banks or depositories.  Portfolio securities purchased outside of the U.S. are maintained in the custody of foreign banks and trust companies who are members of State Street’s Global Custody Network and foreign depositories (foreign sub-custodians).

With respect to foreign sub-custodians, there can be no assurance that a Fund, and the value of its shares, will not be adversely affected by acts of foreign governments, financial or operational difficulties of the foreign sub-custodians, difficulties and costs of obtaining jurisdiction over, or enforcing judgments against, the foreign sub-custodians or application of foreign law to a Fund’s foreign subcustodial arrangements.  Accordingly, an investor should recognize that the noninvestment risks involved in holding assets abroad are greater than those associated with investing in the U.S.

The Funds may invest in obligations of State Street and may purchase or sell securities from or to State Street.

INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

PricewaterhouseCoopers LLP, located at One North Wacker, Chicago, IL 60606, serves as the Funds’ independent registered public accounting firm, providing audit services, tax return review services, and assistance and consultation in connection with the review of various SEC filings.  The Financial Statements incorporated by reference in this SAI have been so incorporated, and the financial highlights included in the Prospectuses have been so included, in reliance upon the reports of PricewaterhouseCoopers LLP and another independent registered public accounting firm given on the authority of that those firms as experts in accounting and auditing.

DETERMINATION OF NET ASSET VALUE

Each Fund determines its net asset value (“NAV”) per share for each class as of the close of the New York Stock Exchange (“Exchange”) (generally 4:00 p.m. Eastern time), each day the Exchange is open.  Currently, the Exchange is closed Saturdays, Sundays and the following holidays:  New Year’s Day, Martin Luther King, Jr. Day, Presidents’ Day, Good Friday, Memorial Day, Independence Day, Labor Day, Thanksgiving and Christmas.  NAV will not be determined on days when the NYSE is closed unless, in the judgment of the Trustees, the NAV of a Fund should be determined on any such day, in which case the determination will be made at 4 p.m., Eastern time.

To calculate the NAV on a given day, a fund values each stock listed or traded on a stock exchange at its latest sale price on that day.  If there are no sales that day, a fund values the security at the most recently quoted bid price.  A fund values each over-the-counter security as of the last sale price for that day.  If a security is traded principally on the Nasdaq Stock Market Inc. (NASDAQ), the SEC-approved NASDAQ Official Closing Price is applied.  When the market price of a security is not readily available, including on days when the Fund determines that the sale or bid price of the security does not reflect that security’s market value, the Fund values the security at a fair value determined in good faith under procedures established by the Board of Trustees.

A Fund values a security at a fair value when an event has occurred after the last available market price and before the close of the NYSE that is expected to materially affects the security’s price.  In the case of foreign securities, this could include events occurring after the close of the foreign market where the securities are traded and before the close of the NYSE.  When a security is valued at a fair value, the value may be higher or lower than the value used by another fund that uses market quotations to price the same securities.  The Trust has retained an independent fair value pricing service to assist in the fair valuation process for securities principally traded in a foreign market in order to adjust for possible changes in value that may occur between the close of the foreign exchange and the time at which NAV is determined.   The use of an independent fair value pricing service is intended to and may decrease the opportunities for time zone arbitrage transactions.  There can be no assurance that the use of an independent fair value pricing service will successfully decrease arbitrage opportunities.  If a security is valued at a “fair value,” that value may be different from the last quoted market price for that security.  The Fund’s foreign securities may trade on days when the NYSE is closed.  A Fund will not determine NAV on days that the NYSE is closed for trading.

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Shares of the Portfolio Funds are valued at their respective net asset values.  The Portfolio Funds generally value securities in their portfolio for which market quotations are readily available at the current market values of those securities (generally the last reported sale price) and all other securities and assets at fair value pursuant to methods established in good faith by the Board of directors or trustees of the Portfolio Fund.

If market quotations of Portfolio Funds are not readily available, or if a quotation is determined not to represent a fair value, management will use a method that the Fund’s Trustees believe accurately reflects a fair value.

Each day, newspapers and other reporting services may publish the share prices of mutual funds at the close of business on the previous day.  Columbia Acorn Fund, Columbia Acorn International, Columbia Acorn International Select and the Portfolio Funds may invest in securities which are primarily listed on foreign exchanges, and therefore may experience trading and changes in NAV on days on which the Funds do not determine NAV due to differences in closing policies among exchanges.  This may significantly affect the NAV of Columbia Acorn Fund, Columbia Acorn International, Columbia Acorn International Select and Columbia Thermostat Fund on days when an investor cannot redeem such securities.  Debt securities generally are valued by a pricing service which determines valuations based upon market transactions for normal, institutional-size trading units of similar securities.  However, in circumstances where such prices are not available or where the Adviser deems it appropriate to do so, an over-the-counter or exchange bid quotation is used.  Securities listed on an exchange or on NASDAQ are valued at the last sale price (or the official closing price as determined by the NASDAQ system, if different, as applicable).  Listed securities for which there were no sales during the day and unlisted securities are valued at the last quoted bid price.  Options are valued at the last sale price or, in the absence of a sale, the mean between the last quoted bid and offering prices.  Short-term obligations with a maturity of 60 days or less are valued at amortized cost pursuant to procedures adopted by the Funds’ Trustees.  The values of foreign securities quoted in foreign currencies are translated into U.S. dollars at the exchange rate on that day.  Fund positions for which market quotations are not readily available and other assets are valued at a fair value as determined by the Valuation Committee in good faith under the procedures approved by of the Funds’ Trustees.

Generally, trading in certain securities (such as foreign securities) is substantially completed each day at various times prior to the close of the Exchange.  Trading on certain foreign securities markets may not take place on all business days in New York, and trading on some foreign securities markets takes place on days which are not business days in New York and on which a Fund’s NAV is not calculated.  The values of these securities used in determining the NAV are computed as of such times.  Also, because of the amount of time required to collect and process trading information as to large numbers of securities issues, the values of certain securities (such as convertible bonds, U.S. government securities, and tax-exempt securities) are determined based on market quotations collected earlier in the day at the latest practicable time prior to the close of the Exchange.  Occasionally, events affecting the value of such a security may occur between such times and the close of the Exchange which may affect the value of the security.  Circumstances in which fair value pricing may be utilized include, but are not limited to:  (i) when a significant event has occurred that may affect the securities of a single issuer, such as a merger, bankruptcy or significant issuer specific development; (ii) when a significant event has occurred that may affect an entire market, such as a natural disaster or significant governmental action; and (iii) when a non-significant event has occurred such as a market’s closing early or not opening, security trading halt or pricing of a nonvalued, restricted or nonpublic security.

HOW TO BUY SHARES

The Prospectuses contain a general description of how investors may buy shares of the Funds and tables of charges.  This SAI contains additional information which may be of interest to investors.  In addition, you may, subject to the approval of the Trust, purchase shares of a Fund with securities that are held in the Fund’s portfolio (or, rarely, with securities that are not currently held in the portfolio but that are eligible for purchase by the Fund [consistent with the Fund’s investment objectives and restrictions]) that have a value that is readily ascertainable in accordance with the Trust’s valuation policies.  Should the Trust approve your purchase of a Fund’s shares with securities, the Trust would follow its purchase-in-kind procedures and would value the securities tendered in payment (determined as of the next close of regular session trading on the New York Stock Exchange after receipt of the purchase order) pursuant to the Trust’s valuation procedures as then in effect, and you would receive the number of Fund shares having a net asset value on the purchase date equal to the aggregate purchase price.

The investment minimum, if any, for initial investments (by purchase, exchange or certain transfers) of each class of shares of the Funds is set forth in the Prospectuses.  The investment minimum does not apply under certain circumstances determined by the Funds to be appropriate from time to time and consistent with the interests of shareholders, including with respect to the following accounts:

·Class A share accounts resulting from the automatic conversion of Class B shares;

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·Accounts established as a result of the limitation on the maximum purchase of Class B shares as described in the Prospectuses;

·Certain specified re-registration of accounts, such as resulting from divorce, death of a shareholder, a change in the shareholder’s broker or certain IRA conversions;

·Investments by the funds of funds or state tuition plans organized under Section 529 of the Internal Revenue Code; and

·Positions resulting from the use of a reinstatement provision described under paragraph 3 of the Net Asset Value Eligibility Guidelines in the Statement.

The Funds will accept unconditional orders for shares to be executed at the public offering price based on the NAV per share next determined after the order is placed in good order.  The public offering price is the NAV plus the applicable sales charge, if any.  In the case of an order for purchase of shares placed through an FSF, the public offering price will be determined on the day the order is placed in good order, but only if the FSF receives the order prior to the time at which shares are valued and transmits it to the Fund before the Fund processes that day’s transactions.  If the FSF fails to transmit before the Fund processes that day’s transactions, the customer’s entitlement to that day’s closing price must be settled between the customer and the FSF.  If the FSF receives the order after the time at which the Fund values its shares, the price will be based on the NAV determined as of the close of the Exchange on the next day it is open.  If funds for the purchase of shares are sent directly to CMS, they will be invested at the public offering price next determined after receipt in good order.  Payment for shares of a Fund must be in U.S. dollars; if made by check, the check must be drawn on a U.S. bank.

Each Fund receives the entire NAV of shares sold.  For shares subject to an initial sales charge, CMD’s commission is the sales charge shown in the Funds’ Prospectuses less any applicable FSF discount.  The FSF discount is the same for all FSFs, except that CMD retains the entire sales charge on any sales made to a shareholder who does not specify a FSF on the Investment Application, and except that CMD may from time to time reallow additional amounts to all or certain FSFs.  CMD generally retains some or all of any asset-based sales charge (distribution fee) or contingent deferred sales charges.  Such charges generally reimburse CMD for any up-front and/or ongoing commissions paid to FSFs.

Checks presented for the purchase of shares of the Fund which are returned by the purchaser’s bank or checkwriting privilege checks for which there are insufficient funds in a shareholder’s account to cover redemption may subject such purchaser or shareholder to a $15 service fee for each check returned.  Checks must be drawn on a U.S. bank and must be payable in U.S. dollars.  Travelers checks, gift checks, credit card convenience checks, credit cards, cash and ban counter (starter checks) are not accepted.

CMS acts as the shareholder’s agent whenever it receives instructions to carry out a transaction on the shareholder’s account.  Upon receipt of instructions that shares are to be purchased for a shareholder’s account, the designated FSF will receive the applicable sales commission.  Shareholders may change FSFs at any time by written notice to CMS, provided the new FSF has a sales agreement with CMD.

Shares credited to an account are transferable upon written instructions in good order to CMS and may be redeemed as described under “How to Sell Shares” in the Prospectuses.  Certificates are not available for any class of shares offered by the Funds.  If you currently hold previously issued share certificates, you may send the certificates to CMS for deposit to your account.

ADDITIONAL INVESTOR SERVICING PAYMENTS

The Funds, along with the transfer agent, distributor and/or investment adviser may pay significant amounts to financial intermediaries (as defined below), including other Bank of America affiliates, for providing the types of services that would typically be provided directly by a Fund’s transfer agent.  The level of payments made to financial intermediaries may vary.  A number of factors may be considered in determining payments to a financial intermediary, including, without limitation, the nature of the services provided to shareholders or retirement plan participants that invest in the Fund through retirement plans.  These services may include sub-accounting, sub-transfer agency or similar recordkeeping services, shareholder or participant reporting, shareholder or participant transaction processing, and/or the provision of call center support (“additional shareholder services”).  These payments for investor servicing support vary by financial intermediary but generally are not expected, with certain limited exceptions, to exceed 0.35% of the total Fund assets in the program on an annual basis for those classes of shares that pay a  

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service fee pursuant to a 12b-1 Plan, and 0.45% of total Fund assets in the program on an annual basis for those classes of shares that do not pay service fees pursuant to a 12b-1 Plan.  As of October 1, 2006, the Trust’s Board has authorized the Fund to pay up to 0.05% of this amount.  Such payments will be made by the Fund to its transfer agent who will in turn make payments to the financial intermediary for the provision of such additional shareholder services.  The Fund’s transfer agent, distributor, investment adviser or their affiliates will pay from their own resources amounts in excess of the amount paid by the Fund to financial intermediaries in connection with the provision of these additional shareholder services and other services.  (See “Additional Financial Intermediary Payments” for more information including a list of the financial intermediaries, as of the date of this SAI, receiving such payments.)

For purposes of this section the term “financial intermediary” includes any broker, dealer, bank, bank trust department, registered investment advisor, financial planner, retirement plan or other third party administrator and any other institution having a selling, services or any similar agreement with CMD or one of its affiliates.

The Funds may also make additional payments to financial intermediaries that charge networking fees for certain services provided in connection with the maintenance of shareholder accounts through the NSCC.

ADDITIONAL FINANCIAL INTERMEDIARY PAYMENTS

As described above and in the section “12b-1 Plan, Contingent Deferred Sales Charges and Conversion of Shares”, financial intermediaries may receive different commissions, sales charge reallowances and other payments with respect to sales of different classes of shares of the Funds. These other payments may include servicing payments to retirement plan administrators and other institutions at rates up to those described below under “Investor Servicing Payments”. For purposes of this section the term “financial intermediary” includes any broker, dealer, bank, bank trust department, registered investment advisor, financial planner, retirement plan or other third party administrator and any other institution having a selling, services or any similar agreement with CMD or one of its affiliates.

CMD, Columbia WAM and their affiliates may pay additional compensation to selected financial intermediaries, including other Bank of America affiliates, under the categories described below. These categories are not mutually exclusive, and a single financial intermediary may receive payments under all categories. A financial intermediary may also receive payments described above in “Additional Investor Servicing Payments”. These payments may create an incentive for a financial intermediary or its representatives to recommend or offer shares of a Fund to its customers. The amount of payments made to financial intermediaries may vary. In determining the amount of payments to be made, CMD, Columbia WAM and their affiliates may consider a number of factors, including, without limitation, asset mix and length or relationship with the financial intermediary, the size of the customer/shareholder base of the financial intermediary, the manner in which customers of the financial intermediary make investments in the Funds, the nature and scope of marketing support or services provided by the financial intermediary (as more fully described below), and the costs incurred by the financial intermediary in connection with maintaining the infrastructure necessary or desirable to support investments in the Funds.

These additional payments by CMD, Columbia WAM or their affiliates are made pursuant to agreements between CMD, Columbia WAM and their affiliates and financial intermediaries and do not change the price paid by investors for the purchase of a share, the amount a Fund will receive as proceeds from such sales, or the distribution (12b-1) fees and expenses paid by the Fund as shown under the heading “Fees and Expenses” in the Fund’s Prospectuses.

Marketing Support Payments

CMD, Columbia WAM or their affiliates may make payments, from their own resources, to certain financial intermediaries, including other Bank of America affiliates, for marketing support services, including, but not limited to, business planning assistance, educating financial intermediary personnel about the Funds and shareholder financial planning needs, placement on the financial intermediary’s preferred or recommended fund list or otherwise identifying a Fund as being part of a complex to be accorded a higher degree of marketing support than complexes not making such payments, access to sales meetings, sales representatives and management representatives of the financial intermediary, client servicing, and systems infrastructure support. These payments are generally based upon one or more of the following factors: average net assets of the mutual funds distributed by CMD attributable to that financial intermediary, gross sales of the mutual funds distributed by CMD attributable to that financial intermediary, reimbursement of ticket charges (fees that a financial intermediary firm charges its representatives for effecting transactions in fund shares) or a negotiated lump sum payment.

While the financial arrangements may vary for each financial intermediary, the marketing support payments to each financial intermediary are generally expected to be between 0.05% and 0.35% on an annual basis for payments based on average net assets of the Funds attributable to the financial intermediary, and between 0.10% and 0.25% on an annual basis for firms receiving a payment based on gross sales of the Funds attributable to the financial intermediary. CMD or its affiliates may make

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payments in materially larger amounts or on a basis materially different from those described above when dealing with other affiliates of Bank of America.  Such increased payments to the other Bank of America affiliate may enable the other Bank of America affiliate to offset credits that it may provide to its customers in order to avoid having such customers pay fees to multiple Bank of America entities in connection with the customer’s investment in the Fund.

As of the date of this SAI, CMD, Columbia WAM or their affiliates had agreed to make marketing support payments to the following financial intermediaries or their affiliates:

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A.G. Edwards & Sons, Inc.

AIG Advisor Group

Ameriprise Financial Services, Inc.

AXA Advisors, LLC

Banc of America Securities LLC

Bank of America, N.A.

Bank of New York

Bear Stearns Securities Corporation

BMO Nesbitt Burns

Brown Brothers Harriman & Co.

Chicago Mercantile Exchange

Citicorp Investment Services

Citigroup Global Markets Inc.

Commonwealth Financial Network

Custodial Trust Company

FAS Corp.

Fidelity Brokerage Services, Inc.

FinancialOxygen, Inc.

Genworth Financial, Inc.

Goldman, Sachs & Co.

Harris Corporation

Huntington Capital Corp.

ING Group

J.J.B. Hilliard, W.L. Lyons, Inc.

Lincoln Financial Advisors Corp.

Linsco/Private Ledger Corp.

Mellon Financial Markets, LLC

Merrill Lynch, Pierce, Fenner & Smith Incorporated

Money Market One

Morgan Stanley & Co. Incorporated

National Financial Services LLC

Pershing LLC

PNC Bank, N.A.

Raymond James & Associates, Inc.

Raymond James Financial Services, Inc.

Security Benefit Life Insurance Company

SEI Investments Inc.

SVB Securities

Summit Bank

Sungard Institutional Brokerage Inc.

Sun Life Assurance Company of Canada

TIAA-CREF Life Insurance Company

Transamerica Corporation

UBS Financial Services Inc.

US Bank National Association

Wachovia Securities LLC

Webster Investment Services, Inc.

Wells Fargo Fund Management LLC

Wells Fargo Corporate Trust Services

CMD, Columbia WAM or their affiliates may enter into similar arrangements with other financial intermediaries from time to time. Therefore, the preceding list is subject to change at any time without notice.

Investor Servicing Payments

CMD, Columbia WAM or their affiliates may also make payments to certain financial intermediaries, including other Bank of America affiliates, that provide investor services to retirement plans and other investment programs to compensate financial intermediaries for a variety of services they provide to such programs. These amounts are in addition to amounts that may be paid on behalf of the Funds (see “Additional Investor Servicing Payments”) and may be in addition to the marketing support payments paid by CMD, Columbia WAM or their affiliates described above. A financial intermediary may perform program services itself or may arrange with a third party to perform program services. These investor services may include sub-accounting, sub-transfer agency, similar shareholder or participant recordkeeping, shareholder or participant reporting, or shareholder or participant transaction processing. Payments by CMD, Columbia WAM or their affiliates for investor servicing support vary by financial intermediary but generally are not expected, with certain limited exceptions, to exceed 0.35% of the total Fund assets in the program on an annual basis for those classes of shares that pay a service fee pursuant to a 12b-1 Plan, and 0.45% of total Fund assets in the program on an annual basis for those classes of shares that do not pay service fees pursuant to a 12b-1 Plan. In addition, CMD, Columbia WAM or their affiliates may make lump sum payments to selected financial intermediaries receiving investor servicing payments in reimbursement of printing costs for literature for participants, account maintenance fees or fees for establishment of the Funds on the financial intermediary’s system or other similar services.

As of the date of this SAI, CMD, Columbia WAM or their affiliates had agreed to make investor servicing payments to the following financial intermediaries or their affiliates:

ABR Retirement Plan Services, Inc.

ACS HR Solutions LLC

ADP Retirement Services

American Century Investments

Ameriprise Financial Services, Inc.

AMG Service Corp.

AST Trust Company

Benefit Plan Administrators

Bisys Retirement Services

Ceridian Retirement Plan Services

Charles Schwab & Co.

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Citigroup Global Markets Inc.

CitiStreet LLC

City National Bank

CNA Trust Corporation

Compensation & Capital Administrative Services, Inc.

CompuSys Erisa Group of Companies

Crown Point Trust Company

Daily Access Concepts, Inc.

Digital Retirement Solutions

Edgewood Services, Inc.

E*Trade Group, Inc.

ExpertPlan

Fidelity Investments Institutional Operations Co.

Fiserv Trust Company

Great West Life & Annuity Co.

GWFS Equities, Inc.

Hartford Life Insurance Company

Hewitt Associates LLC

Invesmart, Inc.

John Hancock Life Insurance Company (U.S.A.)

John Hancock Life Insurance Company of New York

JP Morgan Retirement Plan Services LLC

Lincoln Financial Group

Linsco/Private Ledger Corp.

M&T Securities, Inc.

Marquette Trust Company

Massachusetts Mutual Life Insurance Company

Matrix Settlement & Clearance Services

Mercer HR Services, LLC

Merrill Lynch, Pierce, Fenner & Smith Incorporated

Mid Atlantic Capital Corporation

National Deferred Compensation, Inc.

National Investor Services Corp.

Nationwide Investment Services

New York State Deferred Compensation, Inc.

NYLife Distributors LLC

PNC Advisors

Princeton Retirement Group

RBC Dain Rauscher Inc.

Robert W. Baird & Co., Inc.

Stanton Trust

Strong Funds Distributors, Inc.

Sungard Investment Products, Inc.

The 401k Company

T. Rowe Price Group, Inc.

The Gem Group, L.P.

The Principal Financial Group

The Vanguard Group, Inc.

Unified Trust Company, N.A.

Upromise Investments, Inc.

Wachovia Securities, LLC

Wells Fargo Bank, N.A.

Wells Fargo Funds Management, LLC

Wespac Plan Services, Inc.

Wilmington Trust Corporation

CMD, Columbia WAM or their affiliates may enter into similar arrangements with other financial intermediaries from time to time. Therefore, the preceding list is subject to change at any time without notice.

Other Payments

From time to time, CMD or Columbia WAM, from its own resources, may provide additional compensation to certain financial intermediaries that sell or arrange for the sale of shares of a Fund to the extent not prohibited by laws or the rules of any self-regulatory agency, such as the NASD. Such compensation provided by CMD may include financial assistance to financial intermediaries that enable CMD to participate in and/or present at financial intermediary-sponsored conferences or seminars, sales or training programs for invited registered representatives and other financial intermediary employees, financial intermediary entertainment, and other financial intermediary-sponsored events, and travel expenses, including lodging incurred by registered representatives and other employees in connection with prospecting, retention and due diligence trips. CMD makes payments for entertainment events it deems appropriate, subject to CMD’s internal guidelines and applicable law. These payments may vary upon the nature of the event.

Your financial intermediary may charge you fees or commissions in addition to those disclosed in this SAI. You can ask your financial intermediary for information about any payments it receives from CMD, Columbia WAM and their affiliates and any services it provides, as well as fees and/or commissions it charges. In addition, depending on the financial arrangement in place at any particular time, a financial intermediary and its financial consultants also may have a financial incentive for recommending a particular Fund or share class over others. You should consult with your financial advisor and review carefully any disclosure by the financial intermediary as to compensation received by your financial advisor.

The Fund does not have any arrangements with shareholders or other individuals that would permit frequent purchases or redemptions of fund shares.

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SPECIAL PURCHASE PROGRAMS/INVESTOR SERVICES

The following special purchase programs/investor services may be changed or eliminated at any time.

Automatic Investment Plan.  As a convenience to investors, shares of any Fund may be purchased through the Automatic Investment Plan.  Electronic funds transfers for a fixed amount of at least $50 ($25 for IRA) are used to purchase Fund shares at the public offering price next determined after CMD receives the proceeds.  If your Automatic Investment Plan purchase is by electronic funds transfers, you may request the Automatic Investment Plan purchase for any day.  For share purchases of Columbia Acorn International, Columbia Acorn International Select and Columbia Thermostat, no minimum investment applies to accounts participating in the Automatic Investment Plan.  For share purchases of Columbia Acorn Fund and Columbia Acorn USA for accounts opened prior to December 15, 2003, no minimum investment applies to accounts participating in the Automatic Investment Plan.  For share purchases of Columbia Acorn Select, for accounts opened prior to August 5, 2005, no minimum investment applies to accounts participating in the Automatic Investment Plan.  Further information and application forms are available from FSFs or from CMD.

Automated Dollar Cost Averaging (Classes A, B, C and Z).  The Automated Dollar Cost Averaging program allows you to exchange $100 or more on a monthly basis from any mutual fund distributed by CMD in which you have a current balance of at least $5,000 into the same class of shares of up to five other funds.  Complete the Automated Dollar Cost Averaging section of the Application.  There is no charge for exchanges made pursuant to the Automated Dollar Cost Averaging program.  Exchanges will continue so long as your fund balance is sufficient to complete the transfers.  Your normal rights and privileges as a shareholder remain in full force and effect.  Thus you can buy any fund, exchange between the same Class of shares of funds by written instruction or by telephone exchange if you have so elected and withdraw amounts from any fund, subject to the imposition of any applicable CDSC or sales charges.

Any additional payments or exchanges into your Fund will extend the time of the Automated Dollar Cost Averaging program.

An exchange is generally a capital sale transaction for federal income tax purposes.

You may terminate your program, change the amount of the exchange (subject to the $100 minimum), or change your selection of funds, by telephone or in writing; if in writing by mailing your instructions to Columbia Management Services, Inc., P.O. Box 8081, Boston, MA 02266-8081.

You should consult your FSF or investment adviser to determine whether or not the Automated Dollar Cost Averaging program is appropriate for you.

CMD offers several plans by which an investor may obtain reduced initial or contingent deferred sales charges.  These plans may be altered or discontinued at any time.  See “Programs For Reducing or Eliminating Sales Charges” below for more information.

Tax-Sheltered Retirement Plans (“Retirement Plans”).  CMD offers prototype tax-qualified plans, including Pension and Profit-Sharing Plans for individuals, corporations, employees and the self-employed.  The minimum initial Retirement Plan investment is $25.  Columbia Trust Company (CTC) is the Custodian/Trustee and Plan Sponsor of the Columbia Management prototype plans offered through CMD.  In general, a $20 annual fee is charged.  Detailed information concerning these Retirement Plans and copies of the Retirement Plans are available from CMD.

Participants in Retirement Plans not sponsored by CTC, not including IRAs, may be subject to an annual fee of $20 unless the Retirement Plan maintains an omnibus account with CMS.  Participants in CTC sponsored prototype plans (other than IRAs) who liquidate the total value of their account may also be charged a $20 close-out processing fee payable to CMS.  The close-out fee applies to plans opened after September 1, 1996.  The fee is in addition to any applicable CDSC.  The fee will not apply if the participant uses the proceeds to open a Columbia Management IRA Rollover account in any fund distributed by CMD, or if the Retirement Plan maintains an omnibus account.

Consultation with a competent financial advisor regarding these Retirement Plans and consideration of the suitability of fund shares as an investment under the Employee Retirement Income Security Act of 1974 or otherwise is recommended.

Telephone Address Change Services.  By calling CMS, shareholders or their FSF of record may change an address on a recorded telephone line.  Confirmations of address change will be sent to both the old and the new addresses.  Telephone

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redemption privileges by check are suspended for 30 days after an address change is effected.  Please have your account and taxpayer identification numbers available when calling.

Cash Connection.  Dividends and any other distributions, including Systematic Withdrawal Plan (SWP) payments, may be automatically deposited to a shareholder’s bank account via electronic funds transfer.  Shareholders wishing to avail themselves of this electronic transfer procedure should complete the appropriate sections of the Application.

Automatic Dividend Diversification.  The automatic dividend diversification reinvestment program (ADD) generally allows shareholders to have all distributions from a Fund automatically invested in the same class of shares of another Fund.  An ADD account must be in the same name as the shareholder’s existing open account with the particular Fund.  Call CMS for more information at 1-800-345-6611.

PROGRAMS FOR REDUCING OR ELIMINATING SALES CHARGES

Rights of Accumulation (Columbia Class A and Class T shares only).  Reduced sales charges on Class A and T shares can be effected by combining a current purchase of Class A or Class T shares with prior purchases of other funds and classes distributed by CMD.  The applicable sales charge is based on the combined total of:

1.	the current purchase; and
2.	the value at the public offering price at the close of business on the previous day of all shares of funds for which CMD serves as distributor held by the shareholder.

CMD must be promptly notified of each purchase with respect to which a shareholder is entitled to a reduced sales charge.  Such reduced sales charge will be applied upon confirmation of the shareholder’s holdings by CMS.  A Fund may terminate or amend this Right of Accumulation.

Statement of Intent (Class A, Class E and Class T shares only).  Any person may qualify for reduced sales charges on purchases of Class A, E and T shares made within a thirteen-month period pursuant to a Statement of Intent (“Statement”).  A shareholder may include, as an accumulation credit toward the completion of such Statement, the value of all fund shares held by the shareholder on the date of the Statement in Funds (except shares of any money market fund, unless such shares were acquired by exchange from Class A shares of another non-money market fund)).  The value is determined at the public offering price on the date of the Statement.  Purchases made through reinvestment of distributions do not count toward satisfaction of the Statement.

During the term of a Statement, CMS will hold shares in escrow to secure payment of the higher sales charge applicable to Class A, E or T shares actually purchased.  Dividends and capital gains will be paid on all escrowed shares and these shares will be released when the amount indicated has been purchased.  A Statement does not obligate the investor to buy or a Fund to sell the amount of the Statement.

If a shareholder exceeds the amount of the Statement and reaches an amount which would qualify for a further quantity discount, a retroactive price adjustment will be made at the time of expiration of the Statement (provided the FSF returns to CMD the excess commission previously paid during the thirteen-month period).  The resulting difference in offering price will purchase additional shares for the shareholder’s account at the applicable offering price.

If the amount of the Statement is not purchased, the shareholder shall remit to CMD an amount equal to the difference between the sales charge paid and the sales charge that should have been paid.  If the shareholder fails within twenty days after a written request to pay such difference in sales charge, CMS will redeem escrowed Class A, E or T shares with a value equal to such difference.  The additional FSF commission will be remitted to the shareholder’s FSF of record.

Additional information about and the terms of Statements of Intent are available from your FSF, or from CMS at
1-800-345-6611.

Net Asset Value Eligibility Guidelines (in this section, the “Advisor” refers to Columbia Management Advisors, LLC in its capacity as the Advisor or Administrator to certain Funds).

1.             Employees, brokers and various relationships that are allowed to buy at NAV.  Class A shares of

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certain Funds may be sold at (NAV) to the following individuals, whether currently employed or retired:  Employees of Bank of America Corporation (and its predecessors), its affiliates and subsidiaries; Trustees of funds advised or administered by the Advisor; directors, officers and employees of the Advisor, CMD, or its successors and companies affiliated with the Advisor; Registered representatives and employees of Financial Service Firms (including their affiliates) that are parties to dealer agreements or other sales arrangements with CMD; Nations Funds’ Trustees, Directors and employees of its investment sub-advisers; Broker/Dealers if purchases are in accordance with the internal policies and procedures of the employing broker/dealer and made for their own investment purposes; employees or partners of any contractual service provider to the funds

NAV eligibility for Class A purchase also applies to the families of the parties listed above and their beneficial accounts.  Family members include:  spouse, parent, stepparent, legal guardian, child, stepchild, father-in-law and mother-in-law.

Individuals receiving a distribution from a Bank of America trust, fiduciary, custodial or other similar account may use the proceeds of that distribution to buy Class A shares without paying a front-end sales charge, as long as the proceeds are invested in the funds within 90 days of the date of distribution.

Registered broker/dealer firms that have entered into a dealer agreement with the distributors may buy Class A shares without paying a front-end sales charge for their investment account only.

Banks, trust companies and thrift institutions, acting as fiduciaries.

2.Grandfathered investors.  Any shareholder who owned shares of any fund of Columbia Acorn Trust (formerly named Liberty Acorn Trust) on September 29, 2000 (when all of the then outstanding shares of Columbia Acorn Trust were re-designated Class Z shares) and who since that time has remained a shareholder of any Fund, may purchase Class A shares of any Fund at NAV in those cases where a Columbia Fund Class Z share is not available.

Shareholders of certain Funds that reorganized into the Columbia Funds, formerly named Nations Funds, who were entitled to buy shares at NAV will continue to be eligible for NAV purchases into those Nations Fund accounts opened through August 19, 2005.

Galaxy Fund shareholders prior to December 1, 1995; and shareholders who (i) purchased Galaxy Fund Prime A shares at net asset value and received Class A shares in exchange for those shares during the Galaxy/Liberty Fund reorganization; and (ii) continue to maintain the account in which the Prime A shares were originally purchased.

(For Class T shares only)  Shareholders who (i) purchased Galaxy Fund Retail A shares at net asset value and received Class T shares in exchange for those shares during the Galaxy/Liberty Fund reorganization; and (ii) continue to maintain the account in which the Retail A shares were originally purchased; and Boston 1784 Fund shareholders on the date that those funds were reorganized into Galaxy Funds.

3.Reinstatement.  Subject to the fund policy on trading of fund shares, an investor who has redeemed class A, B, C, D, G or T shares may, upon request, reinstate within 1 year a portion or all of the proceeds of such sales in shares of class A of any fund at the NAV next determined after Columbia Management Services, Inc. received a written reinstatement request and payment.

4.Retirement Plans.  Class A, Class E and Class T shares (Class T shares are not currently open to new investors) of certain funds may also be purchased at reduced or no sales charge by clients of dealers, brokers or registered investment advisors that have entered into arrangements with CMD pursuant to which the funds are included as investments options in wrap fee accounts, other managed agency/asset allocation accounts or programs involving fee-based compensation arrangements, and by participants in certain retirement plans.

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5.Non-U.S. Investors.  Certain pension, profit-sharing or other employee benefit plans offered to non-US investors may be eligible to purchase Class A shares with no sales charge.

6.Reorganizations.  At the Fund’s discretion, NAV eligibility may apply to shares issued in plans of reorganization, such as mergers, asset acquisitions and exchange offers, to which the fund is a party.

7.Rights of Accumulation (ROA).  The value of eligible accounts, regardless of class, maintained by you and you and your immediate family may be combined with the value of your current purchase to reach a sales discount level and to obtain the lower sales charge for your current purchase.

8.Letters of Intent (LOI).  You may pay a lower sales charge when purchasing class A shares by signing a letter of intent. By doing so, you would be able to pay the lower sales charge on all purchases made under the LOI within 13 months. If your LOI purchases are not completed within 13 months, you will be charged the applicable sales charge on the amount you had invested to that date.

Privileges of Insurance Company Separate Accounts.  Class A shares of a Fund may be sold to an insurance company separate account without the imposition of a front-end sales charge provided that the following conditions are met:

1.The insurance company separate account is structured as a pool of IRA accounts managed by the sponsoring insurance company.

2.The sponsoring insurance company makes shares of the Fund available to its contract owner/investors without the imposition of a sales charge;

3.The sponsoring insurance company provides services to the investors in the insurance company separate account, including recordkeeping and administrative services, for which the sponsoring insurance company would be compensated by the Trust’s service providers and not by the Fund; and

Waiver of Contingent Deferred Sales Charges (CDSCs) (in this section, the “Advisor” refers to Columbia Management Advisors, LLC in its capacity as the Advisor or Administrator to certain Funds) (Class A, B, C, D, E, matured F, G and T shares) CDSCs may be waived on redemptions in the following situations with the proper documentation:

1.Death.  CDSCs may be waived on redemptions following the death of (i) the sole shareholder on an individual account, (ii) a joint tenant where the surviving joint tenant is the deceased’s spouse, or (iii) the beneficiary of a Uniform Gifts to Minors Act (UGMA), Uniform Transfers to Minors Act (UTMA) or other custodial account.  If, upon the occurrence of one of the foregoing, the account is transferred to an account registered in the name of the deceased’s estate, the CDSC will be waived on any redemption from the estate account If the account is transferred to a new registration and then a redemption is requested, the applicable CDSC will be charged.

2.Systematic Withdrawal Plan (SWP).  CDSCs may be waived on redemptions occurring pursuant to a monthly, quarterly or semi-annual SWP established with CMS, to the extent the redemptions do not exceed, on an annual basis, 12% of the account’s value at the time that the SWP is established.  Otherwise, CDSCs will be charged on SWP redemptions until this requirement is met.  For redemptions in excess of 12% of the account’s value at the time that the SWP is established, a CDSC will be charged on the SWP redemption.  The 12% limit does not apply if the SWP is set up at the time the account is established, and distributions are being reinvested.  See below under “How to Sell Shares - Systematic Withdrawal Plan.”

3.Disability.  CDSCs may be waived on redemptions occurring after the sole shareholder on an individual account or a joint tenant on a spousal joint tenant account becomes disabled (as defined in Section 72(m)(7) of the Internal Revenue Code).  To be eligible for such waiver, (i) the disability must arise after the purchase of shares (ii) the disabled shareholder must have been under age 65 at the time of the initial determination of disability, and (iii) a letter from a physician must be signed under penalty of perjury stating the nature of the disability.  If the account is transferred to a new registration and then a redemption is requested, the applicable CDSC will be charged.

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4.Death of a trustee.  CDSCs may be waived on redemptions occurring upon dissolution of a revocable living or grantor trust following the death of the sole trustee where (i) the grantor of the trust is the sole trustee and the sole life beneficiary, (ii) death occurs following the purchase and (iii) the trust document provides for dissolution of the trust upon the trustee’s death.  If the account is transferred to a new registration (including that of a successor trustee), the applicable CDSC will be charged upon any subsequent redemption.

5.Returns of excess contributions.  CDSCs may be waived on redemptions required to return excess contributions made to retirement plans or individual retirement accounts, so long as the FSF agrees to return the applicable portion of any commission paid by CMD.

6.Qualified Retirement Plans.  CDSCs may be waived on CMD shares sold by employee benefit plans created according to Section 403(b) of the tax code and sponsored by a non-profit organization qualified under Section 501(c)(3) of the tax code.  To qualify for the waiver, the plan must be a participant in an alliance program that has signed an agreement with Columbia Funds or CMD.

7.Trust Share Taxes.  CDSCs will be waived on redemptions of Class E and F shares (i) where the proceeds are used to directly pay trust taxes, and (ii) where the proceeds are used to pay beneficiaries for the payment of trust taxes.

8.Return of Commission.  CDSCs may be waived on shares sold by intermediaries that are part of the Columbia Funds selling group where the intermediary has entered into an agreement with Columbia Funds not to receive (or to return if received) all or any applicable portion of an upfront commission.

9.Non-U.S. Investors.  CDSCs may be waived on shares sold by or distributions from certain pension, profit-sharing or other employee benefit plans offered to non-U.S. investors.

10.IRS Section 401 and 457.  CDSCs may be waived on shares sold by certain pension, profit-sharing or other employee benefit plans established under Section 401 or 457 of the tax code.

11.Medical Payments.   CDSCs may be waived on shares redeemed for medical payments that exceed 7.5% of income, and distributions made to pay for insurance by an individual who has separated from employment and who has received unemployment compensation under a federal or state program for at least twelve weeks.

12.Plans of Reorganization.  At a Fund’s discretion, CDSCs may be waived for shares issued in plans of reorganization, such as mergers, asset acquisitions and exchange offers, to which the Fund is a party.

13.Charitable Giving Program.  CDSCs may be waived on the sale of Class C shares sold by a non-profit organization qualified under Section 501(c)(3) of the tax code in connection with the Banc of America Capital Management Charitable Giving Program.

14.The CDSC also may be waived where the FSF agrees to return all or an agreed upon portion of the commission earned on the sale of the shares being redeemed.

HOW TO SELL SHARES

Shares may also be sold on any day the Exchange is open, either directly to the Funds or through the shareholder’s FSF.  Sale proceeds generally are sent within seven days (usually on the next business day after your request is received in good form).  However, for shares recently purchased by check, Columbia Acorn may delay selling or delay sending proceeds from your shares for up to 10 days in order to protect the Funds against financial losses and dilution in net asset value caused by dishonored purchase payment checks.

To sell shares directly to the Funds, send a signed letter of instruction or stock power form to CMS, along with any certificates for shares to be sold.  The sale price is the net asset value (less any applicable contingent deferred sales charge or redemption fee) next calculated after the Funds receive the request in proper form.  If you redeem or exchange Class A, B, C or Z shares of Columbia Acorn International or Columbia Acorn International Select that you have owned 60 days or less, that Fund generally will charge you a redemption fee of 2% of the redemption proceeds.  Columbia Acorn International and Columbia Acorn

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International  Select will use the “first-in, first-out” method to determine when shares were purchased.  The redemption fee will be deducted from your redemption proceeds and retained by the Fund to help cover transaction and tax costs that long-term investors may bear when the Fund realizes capital gains as a result of selling securities to meet investor redemptions.  The redemption fee is not imposed on redemptions of shares purchased through reinvestment of dividends and distributions, or exchanges of shares for Class A, B, C or Z shares of a fund distributed by CMD that has a redemption fee.

Signatures must be guaranteed by a bank, a member firm of a national stock exchange or another eligible guarantor that participates in the Medallion Signature Guarantee Program.  Stock power forms are available from FSFs, CMS, and many banks.  Additional documentation is required for sales by corporations, agents, fiduciaries, surviving joint owners, IRA holders and other legal entities.  Call CMS for more information at 1-800-345-6611.

FSFs must receive requests before the time at which the Funds’ shares are valued to receive that day’s price.  FSFs are responsible for furnishing all necessary documentation to CMS and may charge for this service.

Systematic Withdrawal Plan (SWP)

A shareholder may establish a SWP.  A specified dollar amount, share amount or percentage of the then current net asset value of the shareholder’s investment in the Funds designated by the shareholder will be paid monthly, quarterly or semi-annually to a designated payee.  The amount or percentage the shareholder specifies is run against available shares and generally may not, on an annualized basis, exceed 12% of the value, as of the time the shareholder makes the election, of the shareholder’s investment.  Withdrawals of shares of the Funds under a SWP will be treated as redemptions of shares purchased through the reinvestment of Fund distributions, or, to the extent such shares in the shareholder’s account are insufficient to cover Plan payments, as redemptions from the earliest purchased shares of the Funds in the shareholder’s account.  No CDSCs apply to a redemption pursuant to a SWP of 12% or less, even if, after giving effect to the redemption, the shareholder’s account balance is less than the shareholder’s base amount.  Qualified plan participants who are required by Internal Revenue Service regulation to withdraw more than 12%, on an annual basis, of the value of their share account may do so but may be subject to a CDSC ranging from 1% to 5% of the amount withdrawn in excess of 12% annually.  If a shareholder wishes to participate in a SWP, the shareholder must elect to have all of the shareholder’s income dividends and other Fund distributions payable in shares of the Funds rather than in cash.

A shareholder or a shareholder’s FSF of record may establish a SWP account by telephone on a recorded line.  However, SWP checks will be payable only to the shareholder and sent to the address of record.  SWPs from retirement accounts cannot be established by telephone.

A shareholder may not establish a SWP if the shareholder holds shares in certificate form.  Purchasing additional shares (other than through dividend and distribution reinvestment) while receiving SWP payments is ordinarily disadvantageous because of sales charges.  For this reason, a shareholder may not maintain a plan for the accumulation of shares of the Funds (other than through the reinvestment of dividends) and a SWP at the same time.

SWP payments are made through share redemptions, which may result in a gain or loss for tax purposes, may involve the use of principal and may eventually use up all of the shares in a shareholder’s account.

To participate in this program the minimum withdrawal amount is $50 and the minimum account balance is $5,000.

Columbia Acorn may terminate a shareholder’s SWP if the shareholder’s account balance falls below $5,000 due to any transfer or liquidation of shares other than pursuant to the SWP.  SWP payments will be terminated on receiving satisfactory evidence of the death or incapacity of a shareholder.  Until this evidence is received, CMS will not be liable for any payment made in accordance with the provisions of a SWP.

The cost of administering SWPs for the benefit of shareholders who participate in them is borne by the Funds as an expense of all shareholders.

Shareholders whose positions are held in “street name” by certain FSFs may not be able to participate in a SWP.  If a shareholder’s Fund shares are held in “street name”, the shareholder should consult his or her FSF to determine whether he or she may participate in a SWP.  The SWP on accounts held in “street name” must be made payable to the back office via the NSCC.

Telephone Redemptions.  Telephone redemption privileges are described in the Prospectuses.

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Non-Cash Redemptions.  The Trust has elected to be governed by Rule 18f-1 under the 1940 Act pursuant to which it is obligated to redeem shares solely in cash up to the lesser of $250,000 or 1% of the net asset value of a Fund during any 90-day period for any one shareholder.  Redemptions in excess of the above amounts will normally be paid in cash, but may be paid wholly or partly by a distribution in-kind of securities.  If a redemption is made in kind, the redeeming shareholder would bear any transaction costs incurred in selling the securities received.  The Agreement and Declaration of Trust also authorizes the Trust to redeem shares under certain other circumstances as may be specified by the Board of Trustees.

Under certain circumstances, a Portfolio Fund may determine to make payment of a redemption request by Columbia Thermostat Fund wholly or partly by a distribution in kind of securities from its portfolio, instead of cash, in accordance with the rules of the SEC.  In such cases, the Funds may hold securities distributed by a Portfolio Fund until the Adviser determines that it is appropriate to dispose of such securities.

HOW TO EXCHANGE SHARES

The Class A and B shares of the Funds may be exchanged for the same class of shares of any other continuously offered Funds distributed by CMD (with certain exceptions) on the basis of the NAVs per share at the time of exchange.  The Class Z shares of the Funds may be exchanged for the Class A or Class Z shares of any other fund distributed by CMD (with certain exceptions).  Initial exchanges into Columbia Acorn Fund, Columbia Acorn USA and Columbia Acorn Select will be subject to the investment minimums described in the Prospectuses, and will be made at net asset value plus applicable sales charges.  The Prospectus of each fund distributed by CMD describes its investment objective and policies, and shareholders should obtain a Prospectus and consider these objectives and policies carefully before requesting an exchange.  Consult CMS before requesting an exchange.

If you redeem or exchange Class A, B, C or Z shares of Columbia Acorn International or Columbia Acorn International Select that you have owned 60 days or less, that Fund will charge you a redemption fee of 2% of the redemption proceeds.  Columbia Acorn International and Columbia Acorn International Select will use the “first-in” “first-out” method to determine whether the redemption fee applies.  The redemption fee will be deducted from your redemption proceeds and retained by the Fund to help cover transaction and tax costs that long-term investors may bear when the Fund realizes capital gains as a result of selling securities to meet investor redemptions.  The redemption fee is not imposed on redemptions of shares purchased through reinvestment of dividends and distributions, or exchanges of shares for Class A, B, C or Z shares of a fund distributed by CMD that has a redemption fee.

By calling CMS, shareholders or their FSF of record may exchange among accounts with identical registrations, provided that the shares are held on deposit.  During periods of unusual market changes or shareholder activity, shareholders may experience delays in contacting CMS by telephone to exercise the telephone exchange privilege.  Because an exchange involves a redemption and reinvestment in another Columbia fund, completion of an exchange may be delayed under unusual circumstances, such as if the fund suspends repurchases or postpones payment for the fund shares being exchanged in accordance with federal securities law.  CMS will also make exchanges upon receipt of a written exchange request and share certificates, if any.  If the shareholder is a corporation, partnership, agent, or surviving joint owner, CMS will require customary additional documentation.  Prospectuses of the other funds are available from the CMD Literature Department by calling 1-800-426-3750.

A loss to a shareholder may result from an unauthorized transaction reasonably believed to have been authorized.  No shareholder is obligated to use, or authorize the use of, the telephone to execute transactions.

Consult your FSF or CMS.  In all cases, the shares to be exchanged must be registered on the records of the fund in the name of the shareholder desiring to exchange.

Shareholders of the other open-end funds generally may exchange their shares at NAV for the same class of shares of the Fund.  Sales charges may apply for exchanges from money market funds.

An exchange is generally a sale transaction for federal income tax purposes and may result in capital gain or loss.  The exchange privilege may be revised, suspended or terminated at any time.

DISTRIBUTIONS

Distributions on shares of a Fund are invested in additional shares of the same Class of shares of the Fund at net asset value unless the shareholder elects to receive cash.  Regardless of the shareholder’s election, distributions of $10 or less will not be paid in cash, but will be invested in additional shares of the same class of the Fund at net asset value.  Undelivered distribution

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checks returned by the post office will be reinvested in your account.  If a shareholder has elected to receive dividends and/or capital gain distributions in cash and the postal or other delivery service selected by the CMS is unable to deliver checks to the shareholder’s address of record, such shareholder’s distribution option will automatically be converted to having all dividend and other distributions reinvested in additional shares.  No interest will accrue on amounts represented by uncashed distribution or redemption checks.  Shareholders may reinvest all or a portion of a recent cash distribution without a sales charge.  No charge is currently made for reinvestment.

SUSPENSION OF REDEMPTIONS

Columbia Acorn may not suspend shareholders’ right of redemption or postpone payment for more than seven days unless the Exchange is closed for other than customary weekends or holidays, or if permitted by the rules of the SEC during periods when trading on the Exchange is restricted or during any emergency which makes it impracticable for the Funds to dispose of their securities or to determine fairly the value of its net assets, or during any other period permitted by order of the SEC for the protection of investors.

SHAREHOLDER LIABILITY

Under Massachusetts law, shareholders could, under certain circumstances, be held personally liable for the obligations of the Trust.  However, the Declaration disclaims shareholder liability for acts or obligations of the Funds and the Trust and requires that notice of such disclaimer be given in each agreement, obligation, or instrument entered into or executed by the Funds or the Trust’s Trustees.  The Declaration provides for indemnification out of a Fund’s property for all loss and expense of any shareholder held personally liable for the obligations of a Fund.  Thus, the risk of a shareholder incurring financial loss on account of shareholder liability is limited to circumstances (which are considered remote) in which a Fund would be unable to meet its obligations and the disclaimer was inoperative.

The risk of a particular Fund incurring financial loss on account of another Fund  is also believed to be remote, because it would be limited to circumstances in which the disclaimer was inoperative and the other Fund was unable to meet its obligations.

SHAREHOLDER MEETINGS

As described in the section “Organization and History,” Columbia Acorn will not hold annual shareholders’ meetings.  It is expected that every five years the Trustees will call a meeting of shareholders to elect Trustees.  The Trustees may fill any vacancies in the Board of Trustees except that the Trustees may not fill a vacancy if, immediately after filling such vacancy, less than two-thirds of the Trustees then in office would have been elected to such office by the shareholders.  In addition, at such times as less than a majority of the Trustees then in office have been elected to such office by the shareholders, the Trustees must call a meeting of shareholders for the purpose of electing Trustees.  Trustees may be removed from office, with or without cause, by a vote of the holders of two-thirds of the outstanding shares at a meeting duly called for the purpose.  Except as otherwise disclosed in the Prospectuses and this SAI, the Trustees shall continue to hold office and may appoint their successors.

At any shareholders’ meetings that may be held, shareholders of all Funds would vote together, irrespective of Fund, on the election of Trustees, but each Fund would vote separately from the others on other matters, such as changes in the investment policies of that Fund or the approval of the management agreement for that Fund.

PERFORMANCE MEASURES AND INFORMATION

Total Return

Standardized total return and average annual total return.  Total return on a per share basis is the value of the amount of reinvested dividends received per share plus or minus the change in the net asset value per share for a given period.  Total return percentage may be calculated by dividing the value of a share including reinvested distributions at the end of a given period by the value of the share at the beginning of the period and subtracting one.  Average annual total return is the actual return on a $1,000 investment in a particular class of shares of each Fund, made at the beginning of a stated period, adjusted for the maximum sales charge or applicable CDSC for the class of shares of each Fund and assuming that all distributions were reinvested at NAV, converted to an average annual return assuming annual compounding.

Nonstandardized total return.  Nonstandardized total returns may differ from standardized average annual total returns in that they may relate to nonstandardized periods, represent aggregate rather than average annual total returns or may not reflect the sales charge or CDSC.

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For all Funds, total return for a newer class of shares (Classes A, B and C) for periods prior to their inception includes (a) the performance of the newer class of shares since inception (March 3, 2003 for Columbia Thermostat Fund and October 16, 2000 for all other funds) and (b) the performance of the oldest existing class of shares (Class Z) from its inception date up to the date the newer class was offered for sale.  The performance will not be adjusted to take into account the fact that the newer class of shares bears different class specific expenses than the oldest class of shares (e.g., Rule 12b-1 fees).  Therefore, the total rate of return quoted for a newer class of shares will differ from the return that would be quoted had the newer class of shares been outstanding for the entire period over which the calculation is based (i.e., the total rate of return quoted for the newer class will be higher than the return that would have been quoted had the newer class of shares been outstanding for the entire period over which the calculation is based if the class specific expenses for the newer class are higher than the class specific expenses of the oldest class, and the total rate of return quoted for the newer class will be lower than the return that would be quoted had the newer class of shares been outstanding for this entire period if the class specific expenses for the newer class are lower than the class specific expenses of the oldest class).

A Fund’s total return “after taxes on distributions” shows the effect of taxable distributions, but not any taxable gain or loss, on an investment in shares of the Fund for a specified period of time.  A Fund’s total return “after taxes on distributions and sale of Fund shares” shows the effect of both taxable distributions and any taxable gain or loss realized by the shareholder upon the sale of fund shares at the end of a specified period.  To determine these figures, all income, short-term capital gain distributions, and long-term capital gain distributions are assumed to have been taxed at the actual historical federal maximum tax rate.  Those maximum tax rates are applied to distributions prior to reinvestment and the after-tax portion is assumed to have been reinvested in the Funds.  State and local taxes are ignored.  Actual after-tax returns depend on a shareholder’s tax situation and may differ from those shown.  After-tax returns reflect past tax effects and are not predictive of future tax effects.

Average Annual Total Return (After Taxes on Distributions) is computed as follows:

ATVD = P(l+T)n

Where:P = the amount of an assumed initial investment in shares of a Fund

T = average annual total return (after taxes on distributions)

n = number of years from initial investment to the end of the period

ATVD =  ending value of shares held at the end of the period after taxes on fund distributions but not after taxes on redemptions.

Average Annual Total Return (After Taxes on Distributions and Sale of Fund Shares) is computed as follows:

ATVDR = P(l+T)n

Where:P = the amount of an assumed initial investment in shares of a Fund

T = average annual total return (after taxes on distributions and redemption)

n = number of years from initial investment to the end of the period

ATVDR =ending value of shares held at the end of the period after taxes on fund distributions and redemption.

Performance results reflect any voluntary fee waivers or reimbursement of Fund expenses by the Adviser or its affiliates.  Absent these fee waivers or expense reimbursements, performance results would have been lower.

The Funds may also use statistics to indicate volatility or risk.  The premise of each of these measures is that greater volatility connotes greater risk undertaken in achieving performance.  The Funds may quote the following measures of volatility:

Beta.  Beta is the volatility of a fund’s total return relative to the movements of a benchmark index.  A beta greater than one indicates a volatility greater than the index, and a beta of less than one indicates a volatility less than the index.

R-squared.  R-squared reflects the percentage of a fund’s price movements that are explained by movements in the benchmark index.  An R-squared of 1.00 indicates that all movements of a fund’s price are completely explained by movements in the index.  Generally, a higher R-squared will indicate a more reliable beta figure.

Alpha.  Alpha is a measure used to discuss a fund’s relative performance.  Alpha measures the actual return of a fund compared to the expected return of a fund given its risk (as measured by beta).  The expected return of a fund is based on how historical movements of the benchmark index and historical performance of a fund compare to the benchmark index.  The expected return

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is computed by multiplying the advance or decline in a market represented by a fund’s beta.  A positive alpha quantifies the value that a fund manager has added and a negative alpha quantifies the value that a fund manager has lost.

Standard deviation.  Standard deviation quantifies the volatility in the returns of a fund by measuring the amount of variation in the group of returns that make up a fund’s average return.  Standard deviation is generally calculated over a three- or five-year period using monthly returns and modified to present on annualized standard deviation.

Sharpe ratio.  A fund’s Sharpe ratio quantifies its total return in excess of the return of a guaranteed investment (90 day U.S. treasury bills), relative to its volatility as measured by its standard deviation.  The higher a fund’s Sharpe ratio, the better a fund’s returns have been relative to the amount of investment risk it has taken.

Beta and R-squared are calculated by performing a least squares linear regression using three- or five- years of monthly total return figures for each portfolio and benchmark combination.  Alpha is calculated by taking the difference between the average monthly portfolio return and the beta-adjusted average monthly benchmark return.  The result of this calculation is then geometrically annualized.

Other measures of volatility and relative performance may be used as appropriate.  All such measures will fluctuate and do not represent future results.

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APPENDIX I

DESCRIPTION OF BOND RATINGS

(Columbia Thermostat Fund)

A rating of a rating service represents the service’s opinion as to the credit quality of the security being rated.  However, the ratings are general and are not absolute standards of quality or guarantees as to the creditworthiness of an issuer.  Consequently, the Adviser believes that the quality of debt securities in which the Funds invest should be continuously reviewed.  A rating is not a recommendation to purchase, sell or hold a security, because it does not take into account market value or suitability for a particular investor.  When a security has received a rating from more than one service, each rating should be evaluated independently.  Ratings are based on current information furnished by the issuer or obtained by the ratings services from other sources which they consider reliable.  Ratings may be changed, suspended or withdrawn as a result of changes in or unavailability of such information, or for other reasons.

The following is a description of the characteristics of ratings used by Moody’s Investors Service, Inc. (“Moody’s”) and Standard & Poor’s Corporation (“S&P”).

Moody’s Ratings

Aaa bonds are judged to be the best quality.  They carry the smallest degree of investment risk and are generally referred to as “gilt edge”.  Interest payments are protected by a large or by an exceptionally stable margin and principal is secure.  While the various protective elements are likely to change, such changes as can be visualized are most unlikely to impair the fundamentally strong position of such issues.

Aa bonds are judged to be high quality by all standards.  Together with Aaa bonds they comprise what are generally known as high-grade bonds.  They are rated lower than the best bonds because margins of protection may not be as large as in Aaa securities or fluctuation of protective elements may be of greater amplitude or there may be other elements present which make the long-term risks appear somewhat larger than in Aaa securities.

Those bonds in the Aa through B groups that Moody’s believes possess the strongest investment attributes are designated by the symbol Aa1, A1 and Baa1.

A bonds possess many favorable investment attributes and are to be considered as upper-medium-grade obligations.  Factors giving security to principal and interest are considered adequate but elements may be present that suggest a susceptibility to impairment sometime in the future.

Baa bonds are considered as medium grade obligations, i.e., they are neither highly protected nor poorly secured.  Interest payments and principal security appear adequate for the present but certain protective elements may be lacking or may be characteristically unreliable over any great length of time.  Such bonds lack outstanding investment characteristics and in fact, have speculative characteristics as well.

Ba bonds are judged to have speculative elements; their future cannot be considered as well secured.  Often, the protection of interest and principal payments may be very moderate, and thereby not well safeguarded during both good and bad times over the future.  Uncertainty of position characterizes bonds in this class.

B bonds generally lack characteristics of the desirable investment.  Assurance of interest and principal payments or of maintenance of other terms of the contract over any long period of time may be small.

Caa bonds are of poor standing.  Such issues may be in default or there may be present elements of danger with respect to principal or interest.

Ca bonds represent obligations which are speculative in a high degree.  Such bonds are often in default or have other marked shortcomings.

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C bonds are the lowest rated class of bonds and issues so rated can be regarded as having extremely poor prospects of ever attaining any real investment standing.

S&P Ratings

AAA bonds have the highest rating assigned by S&P.  Capacity to pay interest and repay principal is extremely strong.

AA bonds have a very strong capacity to pay interest and repay principal and differ from AAA bonds only in small degree.

A bonds have a strong capacity to pay interest and repay principal, although they are somewhat more susceptible to the adverse effects of changes in circumstances and economic conditions than debt in higher rated categories.

BBB bonds are regarded as having an adequate capacity to pay interest and repay principal.  Whereas they normally exhibit protection parameters, adverse economic conditions or changing circumstances are more likely to lead to a weakened capacity to pay interest and repay principal for bonds in the A category.

BB, B, CCC and CC bonds are regarded as having predominantly speculative characteristics with respect to the issuer’s capacity to pay interest and repay principal in accordance with the terms of the obligation.  BB indicates the lowest degree of speculation and CC the highest degree.  While such debt will likely have some quality and protective characteristics, these are outweighed by large uncertainties or large exposures to adverse conditions.

BB bonds have less near-term vulnerability to default than other speculative issues.  However, they face major ongoing uncertainties or exposure to adverse business, financial, or economic conditions which could lead to inadequate capacity to meet timely interest and principal payments.  The BB rating category is also used for debt subordinated to senior debt that is assigned an actual or implied BBB-rating.

B bonds have a greater vulnerability to default but currently have the capacity to meet interest payments and principal repayments.  Adverse business, financial, or economic conditions will likely impair capacity or willingness to pay interest and repay principal.  The B rating category is also used for debt subordinated to senior debt that is assigned an actual or implied BB or BB- rating.

CCC bonds have a currently identifiable vulnerability to default, and are dependent upon favorable business, financial, and economic conditions to meet timely payment of interest and repayment of principal.  In the event of adverse business, financial, or economic conditions, the bonds are not likely to have the capacity to pay interest and repay principal.  The CCC rating category is also used for debt subordinated to senior debt that is assigned an actual or implied B or B- rating.

CC rating typically is applied to debt subordinated to senior debt that is assigned an actual or implied CCC rating.

C rating typically is applied to debt subordinated to senior debt which is assigned an actual or implied CCC- debt rating.  The C rating may be used to cover a situation where a bankruptcy petition has been filed, but debt service payments are continued.

CI rating is reserved for income bonds on which no interest is being paid.

D bonds are in payment default.  The D rating category is used when interest payments or principal payments are not made on the date due even if the applicable grace period has not expired, unless S&P believes that such payments will be made during such grace period.  The D rating also will be used upon the filing of a bankruptcy petition if debt service payments are jeopardized.

Plus (+) or minus (-) ratings from AA to CCC may be modified by the addition of a plus or minus sign to show relative standing within the major rating categories.

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APPENDIX II

PROXY VOTING POLICY AND PROCEDURES

Columbia Wanger Asset Management, L.P. (“CWAM”)

Policy and Procedures Manual

A.ADMINISTRATION

VOTING CLIENT AND FUND PROXIES

Primary Responsibility	CWAM Stock Analyst/Portfolio Manager
Secondary Responsibility	CWAM Chief Investment Officer
Oversight Responsibility	CWAM Chief Operating Officer and Chief Compliance Officer
Issue Date	8/01/03; as amended by the Columbia Acorn Trust on 3/6/07; as amended by the Wanger Advisors Trust on 3/6/07

POLICY:

All proxies for client securities for which Columbia Wanger Asset Management, L.P. (“CWAM”) has been granted authority to vote shall be voted in a manner considered to be in the best interests of CWAM’s clients, including the Columbia Acorn Funds (“Acorn”) and Wanger Advisor Trust Funds (“WAT”) and their shareholders, without regard to any benefit to CWAM or its affiliates. Where CWAM retains voting authority, as for most client securities, CWAM shall examine each recommendation and vote against management’s recommendation, if, in its judgment, approval or adoption of the recommendation would be expected to impact adversely the current or potential market value of the issuer’s securities.  References to the best interest of a client refer to the interest of the client in terms of the potential economic return on the client’s investment. In the event a client believes that its other interests require a different vote, CWAM shall vote as the client instructs.  In limited cases where in CWAM is required to adhere to regulatory restrictions over ownership limits of certain securities, CWAM may delegate voting authority to an independent third party to vote in the shareholders best interest.

CWAM addresses potential material conflicts of interest by having each individual stock analyst review and vote each proxy for the stocks that he/she follows.  For those proposals where the analyst is voting against management’s recommendation or where there is a variance from the guidelines contained herein, the CWAM Proxy Committee will determine the vote in the best interest of CWAM’s clients, without consideration of any benefit to CWAM, its affiliates or its other clients.

OVERVIEW:

CWAM’s policy is based upon its fiduciary obligation to act in its clients’ best interests and rules under the Investment Company Act of 1940 and the Investment Advisers Act of 1940, which impose obligations with respect to proxy voting on investment advisers and investment companies.

PROCEDURES:

I.ACCOUNT POLICIES

Except as otherwise directed by the client, CWAM or independent third party, ISS delegated to vote in place of CWAM shall vote as follows:

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Separately Managed Accounts

CWAM or ISS shall vote proxies on securities held in its separately managed accounts where the client has given CWAM proxy voting authority.  CWAM currently has authority to vote proxies for the Fairfax County Employees’ Retirement System and Fleet Boston Financial Pension Plan but does not have authority to vote proxies for the State of Oregon.

Columbia Acorn Trust/Wanger Advisors Trust

CWAM or ISS shall vote proxies for portfolio securities held in the Acorn and WAT funds.

CWAM Offshore Funds

CWAM or ISS shall vote proxies on securities held in the Wanger Investment Company PLC (Wanger US Smaller Companies and Wanger European Smaller Companies) and Banque Du Louvre Multi Select Funds.  CWAM has not been given authority to vote proxies on securities held in the New America Small Caps Fund.

CWAM Subadvised Mutual Fund Accounts

The authority to vote proxies on securities held in the RiverSource International Aggressive Growth Fund is reserved to the client.  CWAM or ISS has authority to vote proxies on securities held in the Optimum Small Cap Growth Fund.

II.            PROXY COMMITTEE

CWAM has established a Proxy Committee, which consists of the Chief Investment Officer, the Chief Operating Officer and the Chief Compliance Officer of CWAM.  For proxy voting purposes only, the Proxy Committee will also include the analyst who follows the portfolio security on which to be voted.  The director of domestic research may serve as an alternate member of the Proxy Committee for voting purposes.

The functions of the Proxy Committee shall include, in part,

(a)direction of the vote on proposals where there has been a recommendation to the Committee not to vote according to the Voting Guidelines,

(b)annual review of this Policy and Procedures Manual to ensure consistency with internal policies and legal and regulatory requirements,

(c) annual review of existing Voting Guidelines and development of additional Voting Guidelines to assist in the review of proxy proposals, and

(d)development and modification of Voting Procedures as it deems appropriate or necessary.

In determining the vote on any proposal for which it has responsibility, the Proxy Committee shall act in accordance with the policy stated above.

The Proxy Committee shall create a charter, which shall be consistent with this policy and procedure. The charter shall set forth the Committee’s purpose, membership and operation. The charter shall include procedures prohibiting a member from voting on a matter for which he or she has a conflict of interest by reason of a direct relationship with the issuer or other party affected by a given proposal, e.g., is a portfolio manager for an account of the issuer.

The Proxy Committee shall furnish a copy of the charter to the trustees of Columbia Acorn Trust and of Wanger Advisors Trust and copies of any modifications of the charter or of this Policy and Procedures Manual (including any modification of the Voting Guidelines or Voting Procedures).

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III.           VOTING GUIDELINES

Except under limited circumstances (described in Section IV) where CWAM delegates voting power to an independent third party,  The stock analyst who follows the stock reviews all proxies and ballot items for which CWAM has authority to vote.  The analyst will consider the views of management on each proposal, and if these views are consistent with the CWAM Proxy Policy, will vote in favor of management.  However, each analyst has the responsibility of independently analyzing each proposal and voting each proxy item on a case-by-case basis.

Following are some guidelines CWAM uses with respect to voting on specific matters:

Election of the Board of Directors

CWAM will generally support management’s recommendation for proposals for the election of directors or for an increase or decrease in the number of directors provided a majority of directors would be independent.  When director elections are contested, the analyst’s recommendation and vote should be forwarded to the Proxy Committee for a full vote.

Approval of Independent Auditors

CWAM will generally support management in its annual appointment or approval of independent corporate auditors.  An auditor will usually be thought of as independent unless the auditor receives more than 50% of its revenues from non-audit activities from the company and its affiliates.  In those cases, the vote should be forwarded to the Proxy Committee for a full vote.

Compensation and Equity-Based Compensation Plans

CWAM is generally opposed to compensation plans that substantially dilute ownership interest in a company, provide participants with excessive awards, or have inherently objectionable structural features.  Specifically, for equity-based plans, if the proposed number of shares authorized for option programs (excluding authorized shares of expired or exercised options) exceed 10% of the currently outstanding shares overall or 3% for directors only, the proposal should be referred to the Proxy Committee.  The Committee will then consider the circumstances surrounding the issue and vote in the best interests of the client.

Corporate Governance Issues

CWAM will generally support resolutions to improve shareholder democracy and reduce the likelihood of management entrenchment or conflict-of-interest.  All matters relating to corporate governance will be voted by CWAM on a case-by-case basis using this basic premise.  If an analyst believes that a vote should be made contrary to this premise, then the recommendation should be brought to the Proxy Committee for a full vote.

Social and Corporate Responsibility Issues

CWAM believes that “ordinary business matters” are primarily the responsibility of management and should be approved solely by the corporation’s board of directors.  However, proposals regarding social issues initiated by shareholders asking the company to disclose or amend certain business practices will be analyzed by the appropriate CWAM stock analyst and evaluated on a case-by-case basis.  If an analyst believes that a vote against management is appropriate, he/she should refer the proposal to the full vote by the Proxy Committee.

“Blank Check” Proposals

Occasionally proxy statements ask that shareholders allow proxies to approve any other items in a “blank check” manner.  Analysts should vote against such proposals without referring those to the Proxy Committee.

Special Issues Voting Foreign Proxies

Voting proxies with respect to shares of foreign stocks may involve significantly greater effort and corresponding cost due to the variety of regulatory schemes and corporate practices in foreign countries.  Oftentimes, there may be language barriers, which will mean that an English translation of proxy information may not be available.  Or, a translation must be obtained or

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commissioned before the relevant shareholder meeting.  Time frames between shareholder notification, distribution of proxy materials, book-closure and the actual meeting date may be too short to allow timely action.  In situations like these and in others where CWAM believes that it is uncertain with regards to the information received or because the cost of voting a proxy could exceed the expected benefit, the CWAM analyst may elect to abstain from voting.

In addition, to vote shares in some countries, shares must be “blocked” by the custodian or depository for a specified number of days before the shareholder meeting.  Blocked shares typically may not be traded until the day after the shareholder meeting.  CWAM may refrain from voting shares of foreign stocks subject to blocking restrictions where, in the judgment of the CWAM analyst, the benefit from voting the shares is outweighed by the interest of maintaining client liquidity in the shares.  The decision to vote/not vote is made by the CWAM analyst and is generally made on a case-by-case basis based on relevant factors, including the length of the blocking period, the significance of the holding, and whether the stock is considered a long-term holding.

In cases where the CWAM analyst determines that CWAM should abstain from voting foreign proxies, the CWAM librarian (or a substitute) should document the reasons for abstaining from voting the proxy.

IV.           VOTING PROCEDURES

The Proxy Committee has developed the following procedures to assist in the voting of proxies according to the Voting Guidelines set forth in Section III above. The Proxy Committee may revise these procedures from time to time, as it deems appropriate or necessary to effect the purposes of this Policy and Procedures.

For Columbia Acorn Trust and Wanger Advisors Trust

·CWAM shall use Institutional Shareholder Services (“ISS”), a third party vendor, to implement its proxy voting process.  ISS shall provide record keeping services.  ISS also will provide its internally generated proxy analysis, which can be used to help supplement the CWAM analyst’s research in the proxy voting process.  In limited instances as described later in this section, CWAM may delegate voting power to ISS.

·On a daily basis, the funds’ custodian shall send ISS a holding file detailing each domestic equity holding held in the funds. Information on equity holdings for the international portfolio shall be sent weekly.

·ISS shall receive proxy material information from Proxy Edge or State Street Bank for the funds.  This shall include issues to be voted upon, together with a breakdown of holdings for the funds.

·Whenever a vote is solicited, ISS shall send CWAM a request to vote over a secure website.  The CWAM librarian (or a substitute) will be responsible to check this website daily. The librarian will forward all materials to the appropriate CWAM analyst, who will review and complete the proxy ballot and return to the CWAM librarian or will refer one or more proposals to the Proxy Committee. The analyst will keep documentation (usually copies of email correspondence) of any proposals brought before the Proxy Committee and will instruct the CWAM librarian to vote the proposal in accordance with the Proxy Committee decision.  The analyst will file Proxy Committee documentation under G:\Shared\ProxyComm.  The CWAM librarian will promptly provide ISS the final instructions as how to vote the proxy.

·ISS shall have procedures in place to ensure that a vote is cast on every security holding maintained by the funds on which a vote is solicited unless otherwise directed by the analyst.  On a yearly basis (or when requested), CWAM  shall receive a report from ISS detailing CWAM’s voting for the previous period on behalf of the funds.

For All Other Accounts For Which CWAM Has Voting Authority

·CWAM shall use the respective custodian for the account it advises to vote proxies.  CWAM shall separately maintain voting records for these accounts.

·The CWAM librarian will be responsible for obtaining all proxy materials from the custodian, forward these to the appropriate CWAM analyst who will review and complete the proxy ballot and return to the librarian or will refer one or more proposals

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to the Proxy Committee. The analyst will keep documentation (usually copies of email correspondence) of any proposals brought before the Proxy Committee and will instruct the CWAM librarian to vote the proposal in accordance with the Proxy Committee decision.  The analyst will file Proxy Committee documentation under G:\Shared\ProxyComm.  The CWAM librarian will promptly provide ISS the final instructions as how to vote the proxy.

·The CWAM librarian will be responsible for recording all voting records onto a spreadsheet, which will comprise the detail of how CWAM voted each proxy on behalf of the respective client.  This spreadsheet shall comply with the appropriate record keeping requirements of the applicable rules and will be available to clients upon request.

Delegation of Proxy Voting to an Independent Third Party

From time to time, CWAM may face regulatory or compliance limits on the types or amounts of voting securities that it may purchase or hold for client accounts.  Among other limits, federal, state, foreign regulatory restrictions, or company-specific ownership limits may restrict the total percentage of an issuer’s voting securities that CWAM can hold for clients (collectively, “Ownership Limits”).

The regulations or company-specific documents governing a number of these Ownership Limits Often focus upon holdings in voting securities.  As a result, in limited circumstances in order to comply with such Ownership Limits and/or internal policies designed to comply with such limits, CWAM may delegate proxy voting in certain issuers to ISS, as a qualified, independent third party.

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PART C OTHER INFORMATION

Item 23Exhibits: 

Note:As used herein, the term “Post-effective Amendment” refers to a post-effective amendment to the registration statement of Registrant or its predecessor, The Acorn Fund, Inc., under the Securities Act of 1933 on form S-5, N-1 or N-1A, no. 2-34223.

a.1Agreement and Declaration of Trust. (1)

a.2Amendment No. 1 to Agreement and Declaration of Trust. (3)

a.3Amendment No. 2 to Agreement and Declaration of Trust. (4)

b.Bylaws, as amended effective September 28, 2004. (4)

d.1Organizational Expenses Agreement between Acorn Investment Trust [now named Columbia Acorn Trust] and Wanger Asset Management, L.P. [now named Columbia Wanger Asset Management, L.P.], dated September 3, 1996. (2)

d.2Amended and Restated Administration Agreement between Columbia Acorn Trust (on behalf of Columbia Acorn Fund, Columbia Acorn International, Columbia Acorn USA, Columbia Acorn Select, Columbia Acorn International Select and Columbia Thermostat Fund) and Columbia Wanger Asset Management, L.P., dated August 1, 2004. (5)

d.3Expense Reimbursement Agreement dated September 25, 2002.  (3)

d.4Amended and Restated Investment Advisory Agreement between Columbia Acorn Trust and Columbia Wanger Asset Management, L.P. dated September 27, 2005. (6)

d.5Amended and Restated Investment Advisory Agreement between Columbia Acorn Trust and Columbia Wanger Asset Management, L.P., dated August 1, 2006.

e.1Distribution Agreement between Columbia Acorn Trust and Columbia Management Distributors, Inc. dated August 22, 2005. (6)

e.2Amendment No. 1 to Distribution Agreement between Columbia Acorn Trust and Columbia Management Distributors, Inc. approved July 18, 2006.

f.None.

g.Amended and Restated Master Custodian Agreement between Columbia Acorn Trust and State Street Bank and Trust Company dated September 19, 2005. (6)

h.1Form of Transfer, Dividend Disbursing and Shareholders’ Servicing Agent Agreement between Columbia Acorn Trust, Columbia Management Services, Inc., and Columbia Management Advisors, LLC, dated October 1, 2006.

h.2Letter agreement between Columbia Acorn Trust and Columbia Management Group, LLC, on behalf of Columbia Management Distributor, Inc., Columbia Management Services, Inc., Columbia Wanger Asset Management, L.P. and Columbia Management Advisors, LLC, dated July 31, 2006.

h3Fee waiver agreement between Columbia Acorn Trust, on behalf its series Columbia Thermostat Fund, and Columbia Wanger Asset Management dated May 1, 2007.

h.4Participation Agreement among Merrill Lynch Life Insurance Company, Columbia Acorn Trust and Columbia Funds Distributor, Inc. [now named Columbia Management Distributors, Inc.] dated March 4, 2005. (6)

h.5Amendment No. 1 to Participation Agreement among Merrill Lynch Life Insurance Company, Columbia Acorn Trust and Columbia Management Distributors, Inc. [formerly Columbia Funds Distributor, Inc.] dated March 30, 2007.

h.6Participation Agreement among ML Life Insurance Company of New York, Columbia Acorn Trust and Columbia Funds Distributor, Inc. [now named Columbia Management Distributors, Inc.] dated March 4, 2005. (6)

h.7Amendment No. 1 to Participation Agreement among ML Life Insurance Company of New York, Columbia Acorn Trust and Columbia Management Distributors, Inc. [formerly Columbia Funds Distributor, Inc.] dated March 30, 2007.

i.Consent of Bell, Boyd & Lloyd LLP.

j.Consent of PricewaterhouseCoopers LLP.

k.None.

l.None.

m.1Amended and Restated Rule 12b-1 Distribution Plan dated August 1, 2006. 

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m.2Amended and Restated Rule 12b-1 Plan Implementing Agreement dated September 25, 2002. (3)

n.Amended and Restated Plan Pursuant to Rule 18f-3(d) effective August 1, 2006.   

p.1Code of Ethics of Columbia Wanger Asset Management, L.P., Columbia Acorn Trust and Wanger Advisors Trust, as amended January 2, 2007.

p.2Code of Ethics for Non-Management Trustees, as amended September 26, 2006.

p.3Code of Ethics of Columbia Funds Distributor, Inc. [now named Columbia Management Distributors, Inc.], the principal underwriter of the Funds, effective January 1, 2006. (6)

(1)Previously filed. Incorporated by reference to the exhibit of the same number filed in post-effective amendment No. 53 to the registrant’s registration statement, Securities Act file number 2-34223 (the “Registration Statement”), filed on April 30, 1996.

(2)Previously filed.  Incorporated by reference to Registrant’s post-effective amendment No. 61 to the Registration Statement filed on April 30, 1998.

(3)Previously filed.  Incorporated by reference to Registrant’s post-effective amendment No. 75 to the Registration Statement filed on April 30, 2003.

(4)Previously filed.  Incorporated by reference to Registrant’s post-effective amendment No. 77 to the Registration Statement filed on March 1, 2005.

(5)Previously filed.  Incorporated by reference to Registrant’s post-effective amendment No. 78 to the Registration Statement filed on May 1, 2005.

(6)Previously filed. Incorporated by reference to Registrant’s post-effective amendment No. 79 to the Registration Statement filed on April 28, 2006.

Item 24.Persons Controlled By or Under Common Control with Registrant

The Registrant does not consider that there are any persons directly or indirectly controlled by, or under common control with, the Registrant within the meaning of this item. 

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The information in the prospectus under the caption “Managing the Fund – Investment Adviser” and in the statement of additional information under the caption “Management of the Trust – Investment Adviser” is incorporated by reference. 

Item 25.Indemnification

Article VIII of the Agreement and Declaration of Trust of the Registrant (exhibit a.1) provides in effect that Registrant shall provide certain indemnification of its trustees and officers.  In accordance with Section 17(h) of the Investment Company Act, that provision shall not protect any person against any liability to the Registrant or its shareholders to which he would otherwise be subject by reason of willful misfeasance, bad faith, gross negligence or reckless disregard of the duties involved in the conduct of his office.

Insofar as indemnification for liabilities arising under the Securities Act of 1933 may be permitted to trustees, officers and controlling persons of the Registrant pursuant to the foregoing provisions, or otherwise, the Registrant has been advised that in the opinion of the Securities and Exchange Commission such indemnification is against public policy as expressed in the Act and is, therefore, unenforceable.  In the event that a claim for indemnification against such liabilities (other than the payment by the Registrant of expenses incurred or paid by a trustee, officer or controlling person of the Registrant in the successful defense of any action, suit or proceeding) is asserted by such trustee, officer or controlling person in connection with the securities being registered, the Registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Act and will be governed by the final adjudication of such issue.

The Trust has entered into Indemnification Agreements with each of the independent trustees which provide that the Trust shall indemnify and advance expenses to the independent trustees as provided in the Indemnification Agreements and otherwise to the fullest extent permitted by allocable law.  The Trust will indemnify the independent trustees for and against any and all judgments, penalties, fines and amounts paid in settlement, and all expenses actually and reasonably incurred by the independent trustees in connection with a proceeding to which he or she is a party to by reason of his or her position as an independent trustee.  The Trust will not indemnify the independent trustees for monetary settlements or judgments relating to insider trading, disgorgements of profits pursuant to Section 16(b) of the Securities Exchange Act of 1934, or any liability to the Trust or its shareholders with respect to a final adjudication that an action or omission by an independent trustee was committed in bad faith, involved deliberate dishonesty or that the trustee engaged in willful misfeasance, bad faith, gross negligence or reckless disregard of his or her duties. 

Registrant, its trustees and officers, its investment adviser and persons affiliated with them are insured under a policy of insurance maintained by Registrant and its investment adviser, within the limits and subject to the limitations of the policy, against certain expenses in connection with the defense of actions, suits or proceedings, and certain liabilities that might be imposed as a result of such actions, suits or proceedings, to which they are parties by reason of being or having been such trustees or officers.  The policy expressly excludes coverage for any trustee or officer whose personal dishonesty, fraudulent breach of trust, lack of good faith, or

4

intention to deceive or defraud has been finally adjudicated or may be established or who willfully fails to act prudently.

Item 26.Business and Other Connections of Investment Adviser

The information in the prospectus under the caption “Managing the Fund – Investment Adviser” is incorporated by reference.  Neither Columbia Wanger Asset Management, L.P. nor its general partner has at any time during the past two years been engaged in any other business, profession, vocation or employment of a substantial nature either for its own account or in the capacity of director, officer, employee, partner or trustee. 

Item 27.Principal Underwriters

(a)Columbia Management Distributors, Inc. (“CMD”), a subsidiary of Columbia Management Advisors, LLC, is the Registrant’s principal underwriter.  CMD acts in such capacity for each series of Columbia Funds Series Trust, Columbia Funds Series Trust I, Columbia Funds Institutional Trust, Columbia Funds Master Investment Trust, Nations Separate Account Trust,  Liberty Variable Investment Trust, Stein Roe Variable Investment Trust and Wanger Advisors Trust.

(b)The table below lists each director or officer of the principal underwriter named in the answer to Item 20. 

Name and Principal Business Address*	Positions and Offices with Principal Underwriter	Positions and Offices with Registrant
Ahmed, Yaqub	Vice President	None
Aldi, Andrew	Vice President	None
Anderson, Judith M.	Vice President	None
Ash, James R.	Vice President	None
Banks, Keith T.	Director	None
Ballou, Rick	Senior Vice President	None
Bartlett, John	Managing Director	None
Berretta, Frederick R.	Director	None
Bozek, James	Senior Vice President	None
Brantley, Thomas M.	Senior Vice President-Tax	None
Brown, Beth Ann	Senior Vice President	None
Claiborne, Douglas	Senior Vice President	None

5

Name and Principal Business Address*	Positions and Offices with Principal Underwriter	Positions and Offices with Registrant
Climer, Quentin	Vice President	None
Conley, Brook	Vice President	None
Davis, W. Keith	Senior Vice President – Tax	None
DeFao, Michael	Chief Legal Officer	None
Desilets, Marian	Vice President	Assistant Secretary
Devaney, James	Senior Vice President	None
Devlin, Audrey	Assistant Vice President	None
Difiore, James R.	Assistant Treasurer	None
Dolan, Kevin	Vice President	None
Donovan, M. Patrick	Chief Compliance Officer	None
Doyle, Matthew	Vice President	None
Emerson, Kim P.	Senior Vice President	None
Feldman, David	Managing Director	None
Feloney, Joseph	Senior Vice President	None
Ferullo, Jeanne	Vice President	None
Fisher, James F.	Vice President	None
Fischer, Michael	Assistant Secretary	None
Ford, David C.	Vice President	None
Gellman, Laura D.	Conflicts of Interest Officer	None
Gentile, Russell	Vice President	None
Goldberg, Matthew	Senior Vice President	None
Gubala, Jeffrey	Vice President	None
Guenard, Brian	Vice President	None
Hall, Jennifer	Assistant Vice President	None

6

Name and Principal Business Address*	Positions and Offices with Principal Underwriter	Positions and Offices with Registrant
Hohmann, David	Assistant Secretary	None
Jones, Michael A.	Director, President and Chief Executive Officer	None
Kamin, Eric	Assistant Vice President	None
Lynch, Andrew R.	Managing Director	None
Marcelonis, Sheila	Vice President	None
Martin, William W.	Operational Risk Officer	None
McKinley, Katherine S.	Assistant Secretary	None
Miller, Anthony	Vice President	None
Miller, Gregory M.	Vice President	None
Moberly, Ann R.	Senior Vice President	None
Moon, Leslie	Assistant Vice President	None
Mroz, Gregory	Senior Vice President – Tax	None
Nigrosh, Diane J.	Vice President	None
Owen, Stephanie	Vice President	None
Piken, Keith A.	Senior Vice President	None
Pryor, Elizabeth A.	Secretary	None
Ratto, Gregory	Vice President	None
Rawdon, Gary	Assistant Vice President	None
Reed, Christopher	Senior Vice President	None
Roberts, Amy S.	Director	None
Ross, Gary	Senior Vice President	None
Schortmann, Matthew	Assistant Vice President	None
Scully-Power, Adam	Vice President	None
Seller, Gregory	Vice President	None
Shea, Terence	Vice President	None

7

Name and Principal Business Address*	Positions and Offices with Principal Underwriter	Positions and Offices with Registrant
Sideropoulos, Lou	Senior Vice President	None
Smith, Connie B.	Assistant Secretary	None
Studer, Eric	Senior Vice President	None
Waldron, Thomas	Vice President	None
Walsh, Brian	Vice President	None
Wasp, Kevin	Corporate Ombudsman	None
Weidner, Donna M.	Chief Financial Officer, Treasurer	None
Wess, Valerie	Senior Vice President	None
Wheeler, Eben	Assistant Vice President	None
Wilson, Christopher L.	Senior Vice President	None
Winn, Keith	Senior Vice President	None
Yates, Susan	Vice President	None

* The principal business address for each officer of Columbia Management Distributors, Inc. is One Financial Center, Boston, MA 02111.

Item 28.Location of Accounts and Records

Bruce H. Lauer, Vice President, Secretary and Treasurer
Columbia Acorn Trust
227 West Monroe Street, Suite 3000
Chicago, Illinois 60606

Certain records, including records relating to the Registrant’s shareholders and the physical possession of its securities, may be maintained at the main office of Registrant’s transfer agent, Columbia Funds Services, Inc., located at One Financial Center, Boston, Massachusetts 02111 or custodian, State Street Bank and Trust Company, located at 2 Avenue de Lafayette, Boston, Massachusetts 02111-2900.

Item 29.Management Services

Not applicable.

Item 30.Undertakings

Not applicable.

8

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933 and the Investment Company Act of 1940, the Registrant certifies that it meets all of the requirements for effectiveness of this post-effective amendment pursuant to Rule 485(b) under the Securities Act of 1933 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Chicago and State of Illinois on April 30, 2007.

COLUMBIA ACORN TRUST
By	/s/ Charles P. McQuaid
	Charles P. McQuaid, President

Pursuant to the requirements of the Securities Act of 1933, this amendment to the registration statement has been signed below by the following persons in the capacities and on the dates indicated.

Name	Title		Date
/s/ Margaret M. Eisen	Trustee	)
Margaret M. Eisen		)
		)
/s/ Jerome Kahn, Jr.	Trustee	)
Jerome Kahn, Jr.		)
		)
/s/ Steven N. Kaplan	Trustee	)
Steven N. Kaplan		)
		)
/s/ David C. Kleinman	Trustee	)
David C. Kleinman		)
		)
/s/ Allan B. Muchin	Trustee	)	April 30, 2007
Allan B. Muchin		)
		)
/s/ Robert E. Nason	Trustee and chairman	)
Robert E. Nason		)
		)
/s/ James A. Star	Trustee	)
James A. Star		)
		)
/s/ Ralph Wanger	Trustee	)
Ralph Wanger		)
		)
/s/ Patricia H. Werhane	Trustee	)
Patricia H. Werhane		)
		)
/s/ John A. Wing	Trustee	)
John A. Wing		)
		)
/s/ Charles P. McQuaid	Trustee and President	)
Charles P. McQuaid	(principal executive	)
	officer)	)
		)
/s/ Bruce H. Lauer	Treasurer (principal	)
Bruce H. Lauer	financial and accounting	)
	officer)	)

Index of Exhibits Filed with this Amendment

Exhibit Number	Exhibit
d.5	Amended and Restated Investment Advisory Agreement between Columbia Acorn Trust and Columbia Wanger Asset Management, L.P., dated August 1, 2006.
e.2	Amendment No. 1 to Distribution Agreement between Columbia Acorn Trust and Columbia Management Distributors, Inc. approved July 18, 2006.
h.1	Form of Transfer, Dividend Disbursing and Shareholders’ Servicing Agent Agreement between Columbia Acorn Trust, Columbia Management Services, Inc., and Columbia Management Advisors, LLC, dated October 1, 2006.
h.2	Letter agreement between Columbia Acorn Trust and Columbia Management Group, LLC, on behalf of Columbia Management Distributor, Inc., Columbia Management Services, Inc., Columbia Wanger Asset Management, L.P. and Columbia Management Advisors, LLC, dated July 31, 2006.
h.3	Fee waiver agreement between Columbia Acorn Trust, on behalf of its series Columbia Thermostat Fund, and Columbia Wanger Asset Management dated May 1, 2007.
h.5	Amendment No. 1 to Participation Agreement among Merrill Lynch Life Insurance Company, Columbia Acorn Trust and Columbia Management Distributors, Inc. [formerly Columbia Funds Distributor, Inc.] dated March 30, 2007.
h.7	Amendment No. 1 to Participation Agreement among ML Life Insurance Company of New York, Columbia Acorn Trust and Columbia Management Distributors, Inc. [formerly Columbia Funds Distributor, Inc.] dated March 30, 2007.

i.	Consent of Bell, Boyd & Lloyd LLP.
j.	Consent of PricewaterhouseCoopers LLP.
m.1	Amended and Restated Rule 12b-1 Distribution Plan effective August 1, 2006.
n.	Amended and Restated Plan Pursuant to Rule 18f-3(d) dated August 1, 2006
p.1	Code of Ethics of Columbia Wanger Asset Management, L.P., Columbia Acorn Trust and Wanger Advisors Trust, as amended January 2, 2007.
p.2	Code of Ethics for Non-Management Trustees, as amended September 26, 2006.

EX-99.D.5

Exhibit 99.d.5

AMENDED AND RESTATED INVESTMENT ADVISORY AGREEMENT

Columbia Acorn Trust, a Massachusetts business trust registered under the Investment Company Act of 1940 (the “1940 Act”) as an open-end diversified management investment company (“Columbia Acorn”), and Columbia Wanger Asset Management, L.P., a Delaware limited partnership registered under the Investment Advisers Act of 1940 as an investment adviser (“Columbia WAM”), agree that:

1.             Engagement of Columbia WAM.  The Board of Trustees of Columbia Acorn, including a majority of independent trustees, on behalf of Columbia Acorn, appoints Columbia WAM to furnish investment advisory and other services to Columbia Acorn for its series designated Columbia Acorn Fund, Columbia Acorn International, Columbia Acorn USA, Columbia Acorn Select, Columbia Acorn International Select and Columbia Thermostat Fund (each, a “Fund,” and collectively, the “Funds”), and Columbia WAM accepts that appointment, for the period and on the terms set forth in this agreement.

If Columbia Acorn establishes one or more series in addition to the Funds named above with respect to which it desires to retain Columbia WAM as investment adviser hereunder, and if Columbia WAM is willing to provide such services under this agreement, Columbia Acorn and Columbia WAM may add such new series to this agreement, by written supplement to this agreement.  Such supplement shall include a schedule of compensation to be paid to Columbia WAM by Columbia Acorn with respect to such series and such other modifications of the terms of this agreement with respect to such series as Columbia Acorn and Columbia WAM may agree.  Upon execution of such a supplement by Columbia Acorn and Columbia WAM, that series will become a Fund hereunder and shall be subject to the provisions of this agreement to the same extent as the Funds named above, except as modified by the supplement.

2.             Services of Columbia WAM.

(a)           (i)  Investment Management.  Subject to the overall supervision and control of Columbia Acorn’s board of trustees (the “Board”), Columbia WAM shall have supervisory responsibility for the general management and investment of the Funds’ assets and will endeavor to preserve the autonomy of Columbia Acorn.  Columbia WAM will remain a wholly-owned subsidiary of Columbia Management Group, Inc. (“CMG”) (or its successor) as a Chicago-based management firm.  Columbia WAM shall comply with the 1940 Act and with all applicable rules and regulations of the Securities and Exchange Commission, the provisions of the Internal Revenue Code applicable to the Funds as regulated investment companies, the investment policies and restrictions, portfolio transaction policies and the other statements concerning the Funds in Columbia Acorn’s agreement and declaration of trust, bylaws, and registration statements under the 1940 Act and the Securities Act of 1933 (the “1933 Act”), and policy decisions and procedures adopted by the Board from time to time.

(ii)  Investment Operations.  Columbia WAM will maintain the investment philosophy and research that the Chicago-based management deems appropriate; its research activities will be separate and dedicated solely to Columbia WAM and it will maintain its own domestic and international trading activities.  Columbia WAM will use its best efforts to maintain information systems that will provide timely and uninterrupted operating information and data consistent with all regulatory and compliance requirements.  The Chicago-based management will have the responsibility and considerable latitude to recruit and compensate (on a competitive basis) investment management personnel and to control travel budgets for analysts consistent with its operational and strategic plans while subject to the approval of the management of CMG.

(iii)  Brokerage.  Columbia WAM is authorized to make the decisions to buy and sell securities and other assets for the Funds, to place the Funds’ portfolio transactions with broker-dealers, and to negotiate the terms of such transactions including brokerage commissions on brokerage transactions, on behalf of the Funds.  Columbia WAM is authorized to exercise discretion within the Funds’ policy concerning allocation of its portfolio brokerage, as permitted by law, including but not limited to Section 28(e) of the Securities Exchange Act of 1934, and in so doing shall not be required to make any reduction in its investment advisory fees.  Columbia Acorn hereby authorizes any entity or person associated with

Columbia WAM that is a member of a national securities exchange to effect any transaction on the exchange for the account of a Fund to the extent permitted by and in accordance with Section 11(a) of the Securities Exchange Act of 1934 and Rule 11a2-2(T) thereunder.  Columbia Acorn hereby consents to the retention by such entity or person of compensation for such transactions in accordance with Rule 11a-2(T)(a)(iv).

Columbia WAM may, where it deems it to be advisable, aggregate orders with other securities of the same type to be sold or purchased by one or more Funds with like orders on behalf of other clients of Columbia WAM (as well as clients of other investment advisers affiliated with Columbia WAM, in the event that Columbia WAM and such affiliated investment advisers share common trading facilities).  In such event, Columbia WAM (or Columbia WAM and its affiliated advisers, as the case may be) will allocate the shares so sold or purchased, as well as the expenses incurred in the transaction, in a manner it (or it and they) consider to be equitable and fair and consistent with its (or its or their) fiduciary obligations to clients.

(iv)  Compliance.  Columbia WAM acknowledges the importance that the Board and its compliance committee place on full legal and regulatory compliance by CMG, Columbia WAM, and all other Columbia Acorn service providers and their personnel (collectively, “Providers”) and agrees to (i) fully cooperate with the Board, the compliance committee and the Chief Compliance Officer of Columbia Acorn with all inquiries by Columbia Acorn concerning such compliance by the Providers and (ii) proactively communicate with the Board, the compliance committee and the Chief Compliance Officer of Columbia Acorn concerning material compliance matters and any instance of legal or regulatory non-compliance by the Providers of which Columbia WAM is aware and that Columbia WAM deems to be material.  Such cooperation and communication by Columbia WAM will be done after receipt of an inquiry or upon learning of any such legal or regulatory non-compliance.

(b)           Reports and Information.  Columbia WAM shall furnish to the Board periodic reports on the investment strategy and performance of the Funds and such additional reports and information as the Board or the officers of Columbia Acorn may reasonably request.  Columbia Acorn shall furnish or otherwise make available to Columbia WAM such copies of financial statements, proxy statements, reports, and other information relating to the business and affairs of each Fund as Columbia WAM may, at any time or from time to time, reasonably require in order to discharge its obligations under this agreement.

(c)           Customers of Financial Institutions.  It is understood that Columbia WAM may, but shall not be obligated to, make payments from its own resources to financial institutions (which may include banks, broker-dealers, recordkeepers, administrators and others) that provide, either directly or through agents, administrative and other services with respect to shareholders who are customers of such institutions, including establishing shareholder accounts, assisting Columbia Acorn’s transfer agent with respect to recording purchase and redemption transactions, advising shareholders about the status of their accounts, current yield and dividends declared and such related services as the shareholders or the Funds may request.

(d)           Books and Records.  In compliance with the requirements of Rule 31a-3 under the 1940 Act, Columbia WAM agrees to maintain records relating to its services under this agreement, and further agrees that all records that it maintains for Columbia Acorn are the property of Columbia Acorn and to surrender promptly to Columbia Acorn any of such records upon Columbia Acorn’s request; provided that Columbia WAM may at its own expense make and retain copies of any such records.  Columbia WAM further agrees to preserve for the periods prescribed by Rule 31a-2 under the 1940 Act the records required to be maintained by Rule 31a-1 under the 1940 Act.

(e)           Status of Columbia WAM.  Columbia WAM shall for all purposes herein be deemed to be an independent contractor and not an agent of Columbia Acorn and shall, unless otherwise expressly provided or authorized, have no authority to act for or represent Columbia Acorn in any way.  Columbia WAM agrees to notify the Trust promptly of any change in the identity of Columbia WAM’s general partner.

3.             Administrative Services.  Columbia WAM shall supervise the business and affairs of Columbia Acorn and each Fund and shall provide such services and facilities as may be required for effective administration of

2

Columbia Acorn and the Funds as are not provided by employees or other agents engaged by Columbia Acorn; provided that Columbia WAM shall not have any obligation to provide under this agreement any such services which are the subject of a separate agreement or arrangement between Columbia Acorn and Columbia WAM, any affiliate of Columbia WAM, or any third party administrator.

4.             Use of Affiliated Companies and Subcontractors.  In connection with the services to be provided by Columbia WAM under this agreement, Columbia WAM may, to the extent it deems appropriate, and subject to compliance with the requirements of applicable laws and regulations and upon receipt of approval of the Trustees, make use of (i) its affiliated companies and their directors, trustees, officers, and employees and (ii) subcontractors selected by Columbia WAM, provided that Columbia WAM shall supervise and remain fully responsible for the services of all such third parties in accordance with and to the extent provided by this agreement.  All costs and expenses associated with services provided by any such third parties shall be borne by Columbia WAM or such parties.

5.             Expenses to be Paid by Columbia Acorn.  Except as otherwise provided in this agreement or any other contract to which Columbia Acorn is a party, Columbia Acorn shall pay all expenses incidental to its organization, operations and business, including, without limitation:

(a)all charges of depositories, custodians, sub-custodians and other agencies for the safekeeping and servicing of its cash, securities and other property and of its transfer agents and registrars and its dividend disbursing and redemption agents, if any;

(b)all charges of its administrator, if any;

(c)all charges of legal counsel and of independent auditors;

(d)all compensation of trustees other than those affiliated with Columbia WAM or Columbia Acorn’s administrator, if any, and all expenses incurred in connection with their services to Columbia Acorn;

(e)all expenses of preparing, printing and distributing notices, proxy solicitation materials and reports to shareholders of the Funds;

(f)all expenses of meetings of shareholders of the Funds;

(g)all expenses of registering and maintaining the registration of Columbia Acorn under the 1940 Act and of shares of the Funds under the 1933 Act, including all expenses of preparation, filing and printing of annual or more frequent revisions of the Funds’ registration statements under the 1940 Act and 1933 Act, and of supplying each then existing shareholder or beneficial owner of shares of the Funds of a copy of each revised prospectus or supplement thereto, and of supplying a copy of the statement of additional information upon request to any then existing shareholder;

(h)all costs of borrowing money;

(i)all expenses of publication of notices and reports to shareholders and to governmental bodies or regulatory agencies;

(j)all taxes and fees payable to federal, state or other governmental agencies, domestic or foreign, and all stamp or other taxes;

(k)all expenses of printing and mailing certificates for shares of a Fund;

(l)all expenses of bond and insurance coverage required by law or deemed advisable by the Board;

(m)          all expenses of qualifying and maintaining qualification of, or providing appropriate notification of intention to sell relating to, shares of the Funds under the securities laws of the various states and other jurisdictions, and of registration and qualification of Columbia Acorn under any other laws applicable to Columbia Acorn or its business activities;

(n)           all fees, dues and other expenses related to membership of Columbia Acorn in any trade association or other investment company organization; and

3

(o)any extraordinary expenses.

In addition to the payment of expenses, Columbia Acorn shall also pay all brokers’ commissions and other charges relating to the purchase and sale of portfolio securities for each Fund.

6.             Allocation of Expenses Paid by Columbia Acorn.  Any expenses paid by Columbia Acorn that are attributable solely to the organization, operation or business of a Fund or Funds shall be paid solely out of the assets of that Fund or Funds.  Any expense paid by Columbia Acorn that is not solely attributable to a Fund or Funds, nor solely to any other series of Columbia Acorn, shall be apportioned in such manner as Columbia Acorn or Columbia Acorn’s administrator determines is fair and appropriate, or as otherwise specified by the Board.

7.             Expenses to be Paid by Columbia WAM.  Columbia WAM shall furnish to Columbia Acorn, at Columbia WAM’s own expense, office space and all necessary office facilities, equipment and personnel required to provide its services pursuant to this agreement.  Columbia WAM shall also assume and pay all expenses of placement of securities orders and related bookkeeping.

8.             Compensation of Columbia WAM.  For the services to be rendered and the expenses to be assumed and to be paid by Columbia WAM under this agreement, Columbia Acorn on behalf of the respective Funds shall pay to Columbia WAM fees accrued daily and paid monthly at the annual rates (as a percentage of the Fund’s net assets) shown below:

Columbia Acorn Fund

Assets	Rate of Fee
Up to $700 million	0.740	%
$700 million to $2 billion	0.690	%
$2 billion to $6 billion	0.640	%
$6 billion and over	0.630	%

Columbia Acorn International

Assets	Rate of Fee
Up to $100 million	1.190	%
$100 million to $500 million	0.940	%
$500 million and over	0.740	%

Columbia Acorn USA

Assets	Rate of Fee
Up to $200 million	0.940	%
$200 million to $500 million	0.890	%
$500 million to $2 billion	0.840	%
$2 billion to $3 billion	0.800	%
$3 billion and over	0.700	%

Columbia Acorn Select

Assets	Rate of Fee
Up to $700 million	0.850	%
$700 million to $2 billion	0.800	%
$2 billion to $3 billion	0.750	%
$3 billion and over	0.700	%

4

Columbia Acorn International Select

All Assets 0.940 %

Columbia Thermostat Fund

All Assets 0.100 %

The fees attributable to each Fund shall be a                 separate charge to such Fund and shall be the several (and not joint or joint and several) obligation of each such Fund.

9.             Services of Columbia WAM Not Exclusive.  The services of Columbia WAM to Columbia Acorn under this agreement are not exclusive, and Columbia WAM shall be free to render similar services to others so long as its services under this agreement are not impaired by such other activities.  The principal investment management focus and responsibilities of Columbia WAM’s portfolio managers and analysts will be dedicated to Columbia Acorn and Wanger Advisors Trust.

10.           Services Other Than as Adviser.  Within the limits permitted by law, Columbia WAM or an affiliate of Columbia WAM may receive compensation from Columbia Acorn for other services performed by it for Columbia Acorn which are not within the scope of the duties of Columbia WAM under this agreement, including the provision of brokerage services.

11.           Standard of Care.  To the extent permitted by applicable law, neither Columbia WAM nor any of its partners, officers, agents, employees or affiliates shall be liable to Columbia Acorn or its shareholders for any loss suffered by Columbia Acorn or its shareholders as a result of any error of judgment, or any loss arising out of any investment, or as a consequence of any other act or omission of Columbia WAM or any of its affiliates in the performance of Columbia WAM’s duties under this agreement, except for liability resulting from willful misfeasance, bad faith or gross negligence on the part of Columbia WAM or such affiliate, or by reason of reckless disregard by Columbia WAM or such affiliate of the obligations and duties of Columbia WAM under this agreement.

12.           Effective Date, Duration and Renewal.  This agreement shall become effective on August 1, 2006.  Unless terminated as provided in Section 13, this agreement shall continue in effect as to a Fund until July 31, 2007 and thereafter from year to year only so long as such continuance is specifically approved at least annually (a) by a majority of those trustees who are not interested persons of Columbia Acorn or of Columbia WAM, voting in person at a meeting called for the purpose of voting on such approval, and (b) by either the Board or vote of the holders of a “majority of the outstanding shares” of that Fund (which term as used throughout this agreement shall be construed in accordance with the definition of “vote of a majority of the outstanding voting securities of a company” in section 2(a)(42) of the 1940 Act).

13.           Termination.  This agreement may be terminated as to a Fund at any time, without payment of any penalty, by the Board, or by a vote of the holders of a majority of the outstanding shares of that Fund, upon     60 days’ written notice to Columbia WAM.  This agreement may be terminated by Columbia WAM at any time upon 60 days’ written notice to Columbia Acorn.  This agreement shall terminate automatically in the event of its assignment (as defined in Section 2(a)(4) of the 1940 Act).

14.Amendment.  This agreement may be amended in accordance with the 1940 Act.

15.           Non-Liability of Trustees and Shareholders.  A copy of the declaration of trust of Columbia Acorn is on file with the Secretary of The Commonwealth of Massachusetts, and notice is hereby given that this instrument is executed on behalf of Columbia Acorn by its officers as officers and not individually.  All obligations of Columbia Acorn hereunder shall be binding only upon the assets of Columbia Acorn (or the appropriate Fund) and shall not be binding upon any trustee, officer, employee, agent or shareholder of Columbia Acorn.  Neither the

5

authorization of any action by the trustees or shareholders of Columbia Acorn nor the execution of this agreement on behalf of Columbia Acorn shall impose any liability upon any trustee, officer or shareholder of Columbia Acorn.

16.           Use of Manager’s Name.  Columbia Acorn may use the name “Columbia” or any other name derived from the name “Columbia” only for so long as this agreement or any extension, renewal or amendment hereof remains in effect, including any similar agreement with any organization that shall remain affiliated with CMG and shall have succeeded to the business of Columbia WAM as investment adviser.  At such time as this agreement or any extension, renewal or amendment hereof, or such other similar agreement shall no longer be in effect, Columbia Acorn will (by amendment of its agreement and declaration of trust if necessary) cease to use any name derived from the name “Columbia” or otherwise connected with Columbia WAM, or with any organization that shall have succeeded to Columbia WAM’s business as investment adviser.

17.           Notices.  Any notice, demand, change of address or other communication to be given in connection with this agreement shall be given in writing and shall be given by personal delivery, by registered or certified mail or by transmittal by facsimile or other electronic medium addressed to the recipient as follows (or at such other address or addresses as a party may provide to the other from time to time, by notice):

If to Columbia WAM:	Columbia Wanger Asset Management, L.P. Attention: Bruce H. Lauer 227 West Monroe Street, Suite 3000 Chicago, Illinois 60606 Telephone: 312 634-9200 Facsimile: 312 634-0016
	with a copy to:
If to Columbia Acorn:	Columbia Acorn Trust 227 West Monroe Street, Suite 3000 Chicago, Illinois 60606 Telephone: 312 634-9200 Facsimile: 312 634-1919
	with a copy to: Bell, Boyd & Lloyd LLC Attention: Cameron S. Avery 70 West Madison Street, Suite 3100 Chicago, Illinois 60602 Telephone: 312/372-1121 Facsimile: 312/827-8000

All notices shall be conclusively deemed to have been given on the day of actual delivery thereof and, if given by registered or certified mail, on the fifth business day following the deposit thereof in the mail and, if given by facsimile or other electronic medium, on the day of transmittal thereof (upon electronic confirmation of receipt thereof).

18.           Governing Law.  This agreement shall be construed and interpreted in accordance with the laws of the State of Illinois and the laws of the United States of America applicable to contracts executed and to be performed therein.

6

Dated as of August 1, 2006
COLUMBIA ACORN TRUST
By	/s/ Charles P. McQuaid
	Charles P. McQuaid
COLUMBIA WANGER ASSET MANAGEMENT, L.P.
By	WAM Acquisition GP, Inc.
Its	General Partner
By	/s/ Bruce H. Lauer
	Bruce H. Lauer

7

EX-99.E.2

Exhibit 99.e.2

AMENDMENT NO. 1 TO DISTRIBUTION AGREEMENT

This Amendment No. 1 to the Distribution Agreement (the “Amendment”) is hereby made by and between Columbia Acorn Trust (the “Trust”), a Massachusetts business trust and Columbia Management Distributors, Inc. (“CMDI”), a Massachusetts corporation.  This Amendment is dated as of July 18, 2006.  Capitalized terms not defined herein shall have the meaning ascribed to them in the Distribution Agreement dated as of August 22, 2005 (the “Agreement”).

WHEREAS, the Trust has appointed CMDI as the Distributor for each series of the Trust listed in Schedule A attached thereto, each a registered investment company;

WHEREAS, the parties to the Agreement desire to amend the Agreement to include the following representations and warranties regarding CMDI’s anti-money laundering program and/or procedures;

WHEREAS, the parties to the Agreement also desire to amend Schedule II attached thereto to reflect the compensation CMDI is entitled to receive from the Trust;

NOW THEREFORE, in consideration of the mutual promises and covenants set forth herein, the parties hereto agree:

1.  To restate Section 4 of the Agreement as follows:

4.             Anti-Money Laundering Program.  CMDI represents and warrants to the Trust that:

(a)it has established and maintains, and will continue to maintain and operate, an anti-money laundering program and/or procedures (including the Trust’s customer identification program) in accordance with all applicable laws, rules and regulations of its own jurisdiction including, where applicable, the Bank Secrecy Act (as amended by the USA PATRIOT Act of 2001 (the “Act”)).   CMDI further represents that it will adopt appropriate policies, procedures and internal controls to be fully compliant with any additional laws, rules or regulations, including the Act, to which it may become subject, including compliance with the rules recently adopted by the Treasury Department regarding foreign financial institutions that became effective July 5, 2006;

(b)it applies, and will continue to apply, its anti-money laundering program and/or procedures to all customers/investors of the Funds, and will take appropriate steps in accordance with the laws of its own jurisdiction to ensure that all relevant documentation is retained, as required, including identification relating to those customers/investors;

(c)it will provide an annual certification to the Trust confirming that it has implemented an anti-money laundering program and/or procedures as described in paragraph (a), and that it has performed, and intends to continue to perform, the requirements of the Trust’s Customer Identification Procedures.  CMDI will

provide to the Trust periodic reports on the implementation of the anti-money laundering program and its ability to monitor the program;

(d)it complies with the United States regulations imposed by the Treasury Departments’ Office of Foreign Assets Control (“OFAC”) including but not limited to, the International Emergency Economic Powers Act, 50 U.S.C. §1701 et seq., The Trading with the Enemy Act, 50 U.S.C. App. 1 et seq., and any Executive Orders or regulations promulgated thereunder, which prohibit, among other things, the engagement in transactions with, holding the securities of, and the provision of services to certain embargoed foreign countries and specially designated nationals, specially designated narcotics traffickers, terrorist sanctions, and other blocked parties;

(e)it does not believe, has no current reason to believe and will notify the Trust immediately if it comes to have reason to believe that any shareholder of any Fund is engaged in money-laundering activities or is associated with any terrorist or other individual, entity or organization sanctioned by the United States or the jurisdictions in which it does business, or appear on any lists of prohibited persons, entities, and jurisdictions maintained and administered by OFAC; and

(f)if it has delegated to any third party or parties any of its tasks under its agreement with the Trust, CMDI has secured from that third party such representations, warranties and undertakings as are necessary to permit CMDI to provide the representations, warranties and covenants as are set forth in subparagraphs (a)-(e) above.

2.  Schedule II.  Pursuant to Section 8.1 of the Agreement, the parties hereto mutually agree that Schedule II attached to the Agreement be deleted and replaced in its entirety by the Schedule II attached to this Amendment.

IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be duly executed and sealed as of the date first above written.

COLUMBIA ACORN TRUST
By:	/s/ Bruce H. Lauer
Name:	Bruce H. Lauer
Title:	Vice President, Secretary
	and Treasurer
COLUMBIA MANAGEMENT DISTRIBUTORS, INC.
By:	/s/ Donald E. Froude
Name:	Donald E. Froude
Title:	President, Intermediary Distribution

SCHEDULE II

COMPENSATION

Share Class	Fee as a percentage of daily net assets
Class A	25 basis points
Class B	75 basis points
Class C	100 basis points

Approved:  July 18, 2006

EX-99.H.1

Exhibit 99.h.1

TRANSFER, DIVIDEND DISBURSING AND

SHAREHOLDERS’ SERVICING AGENT AGREEMENT

This agreement (the “Agreement”) is made as of this 1 day of Oct, 2006, by and between Columbia Acorn Trust, a Massachusetts business trust (the “Trust”) acting on behalf of its series all as listed on Schedule A hereto (as the same may from time to time be amended to add or delete one or more series of the Trust) (each series of the Trust, if any, being hereinafter referred to as a “Fund”), Columbia Management Services, Inc., a Massachusetts corporation (“CMS”), and Columbia Management Advisors, LLC (“CMA”), a Delaware limited liability company.

WHEREAS, the Trust is a registered investment company and desires that CMS perform certain services for the Funds; and

WHEREAS, CMS is willing to perform such services upon the terms and subject to the conditions set forth herein.

NOW THEREFORE, in consideration of the mutual promises and covenants set forth herein, the parties hereto agree as follows:

1.Appointment.  The Trust hereby appoints CMS to act as transfer agent, dividend disbursing Agent and shareholders’ servicing Agent for the Funds and as agent for the Funds’ shareholders in connection with the shareholder plans described in the Prospectus (as defined below), and CMS accepts such appointments and will perform the respective duties and functions of such offices in the manner hereinafter set forth.

Notwithstanding such appointments, however, the parties hereto agree that CMA may, upon thirty (30) days prior written notice to the Trust, assume such duties and functions itself.  In such event, CMA shall have all of the rights and obligations of CMS hereunder.  However, whether or not CMA assumes such duties and functions, CMA guarantees the performance of CMS hereunder and shall be responsible financially and otherwise to the Trust for the performance by CMS of its obligations under this Agreement.

2.Compensation.  The Trust shall pay to CMS, or to such person(s) as CMS may from time to time instruct, for services rendered and costs incurred in connection with the performance of duties hereunder, such compensation and reimbursement as may from time to time be approved by vote of the Trustees of the Trust.

Schedule B hereto sets forth the compensation and reimbursement arrangements to be effective as of the date of this Agreement, and the treatment of all interest earned with respect to balances in the accounts maintained by CMS referred to in Sections 6, 10 and 11 of this Agreement, net of any charges imposed by the bank(s) at which CMS maintains such accounts.

3.Copies of Documents.  The Trust will furnish CMS with copies of the following documents:  the Declaration of Trust of the Trust and all amendments thereto; and the Trust’s Registration Statement as in effect on the date hereof under the Securities Act of 1933, as amended, and the Investment Company Act of 1940, as amended, and all amendments or

supplements thereto hereafter filed.  The Prospectus(es) and Statement(s) of Additional Information contained in such Registration Statement, as from time to time amended and supplemented, together are herein collectively referred to as the “Prospectus.”

4.Share Certificates.  If the Trustees of the Trust shall have resolved that all of the Trust’s (or a particular Fund’s) shares of beneficial interest, or all of the shares of a particular series or class of such shares, shall be issued in certificated form, CMS shall maintain a sufficient supply of blank share certificates representing such shares, in the form approved from time to time by the Trustees of the Trust.  Such blank share certificates shall be properly signed, manually or by facsimile signature, by the duly authorized officers of the Trust, and shall bear the seal or facsimile thereof of the Trust; and notwithstanding the death, resignation or removal of any officer of the Trust authorized to sign such share certificates, CMS may continue to countersign certificates which bear the manual or facsimile signature of such officer until otherwise directed by the Trust.

5.Lost or Destroyed Certificates.  In case of the alleged loss or destruction of any shareholder certificate, no new certificate shall be issued in lieu thereof, unless there shall first be furnished to CMS an affidavit of loss or non-receipt by the holder of shares with respect to which a certificate has been lost or destroyed, supported by an appropriate bond satisfactory to CMS and the Trust issued by a surety company satisfactory to CMS.

6.Receipt of Funds for Investment.  CMS will maintain one or more accounts with its cash management bank into which it will deposit funds payable to CMS as agent for, or otherwise identified as being for the account of, the Funds or the Distributor, prior to crediting such funds to the respective accounts of the Funds and the Distributor.  Thereafter, CMS will determine the amount of any such funds due a Fund (equal to the number of Fund shares sold by the Fund computed pursuant to paragraph 7 hereof, multiplied by the net asset value of a Fund share next determined after receipt of such purchase order) and the Distributor (equal to the sales charge applicable to such sale computed pursuant to paragraph 9 hereof), respectively, deposit the portion due the Distributor in its account as may from time to time be designated by the Distributor, deposit the net amount due the Fund in the Fund’s account with its custodian (the “Custodian”), notify the Distributor (such notification to the Distributor to include the amount of such sales charge to be remitted by the Distributor to the dealer participating in the sale, computed pursuant to paragraph 9 hereof) and the Fund, respectively, of such deposits, such notification to be given as soon as practicable on the next business day stating the total amount deposited to said accounts during the previous business day.  Such notification shall be confirmed in writing.

7.Shareholder Accounts.  Upon receipt of any funds referred to in paragraph 6 hereof, CMS will compute the number of shares purchased by the shareholder according to the net asset value of Fund shares next determined after such receipt less the applicable sales charge, calculated pursuant to paragraph 9 hereof; and

(a)in the case of a new shareholder, open and maintain an open account for such shareholder in the name or names set forth in the subscription application form;

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(b)if the Trustees of the Trust have resolved that all of the Trust’s shares of beneficial interest, or all of the shares of a particular series or class, shall be issued in certificated form, and if specifically requested in writing by the shareholder, countersign, issue and mail, by first class mail, to the shareholder at his or her address set forth in the shareholder records of the Trust maintained by CMS a share certificate for full shares purchased.

(c)send to the shareholder a confirmation indicating the amount of full and fractional shares purchased (in the case of fractional shares, rounded to three decimal places) and the price per share; and

(d)in the case of a request to establish an accumulation plan, withdrawal plan, group plan or other plan or program being offered by the Fund’s Prospectus, open and maintain such plan or program for the shareholder in accordance with the terms thereof;

all subject to any reasonable instructions which the Distributor or the Trust may give to CMS with respect to rejection of orders for shares.

8.Unpaid Checks.  In the event that any check or other order for payment of money on the account of any shareholder or new investor is returned for any reason, CMS will take such steps, including imposition of a reasonable processing or handling fee on such shareholder or investor, as CMS may, in CMS’s discretion, deem appropriate, or as the Trust or the Distributor may instruct CMS.

9.Sales Charge.  In computing the number of shares to credit to the account of a shareholder pursuant to paragraph 7 hereof, CMS will calculate the total of the applicable Distributor and representative sales charges, commission or other amount, if any, with respect to each purchase as set forth in the Prospectus and in accordance with any notification filed with respect to combined and accumulated purchases.  CMS will also determine the portion of each sales charge, commission or other amount, if any, payable by the Distributor to the dealer or other amount, payable by the Distributor to the dealer participating in the sale in accordance with such schedules as are from time to time delivered by the Distributor to CMS.

10.Dividends and Distributions.  The Trust will promptly notify CMS of the declaration of any dividends or distribution with respect to Fund shares, the amount of such dividend or distribution, the date each such dividend or distribution shall be paid, and the record date for determination of shareholders entitled to receive such dividend or distribution.  As Dividend Disbursing Agent, CMS will, on or before the payment date of any such dividend or distribution, notify the Custodian of the estimated amount of cash required to pay such dividend or distribution, and the Trust agrees that on or before the mailing date of such dividend or distribution it will instruct the Custodian to make available to CMS sufficient funds therefor in the dividend and distribution account maintained by CMS with the Custodian.  As Dividend Disbursing Agent, CMS will prepare and distribute to shareholders any funds to which they are entitled by reason of any dividend or distribution and, in the case of shareholders entitled to receive additional shares by reason of any such dividend or distribution, CMS will make appropriate credits to their accounts and prepare and mail to shareholders a confirmation statement and, if required, a certificate in respect of such additional shares.

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11.Repurchase and Redemptions.  CMS will receive and stamp with the date of receipt all certificates and requests delivered to CMS for repurchase or redemption of shares and CMS will process such repurchases as agent for the Distributor and such redemptions as agent for the Trust as follows:

(a)If such certificate or request complies with standards for repurchase or redemption approved from time to time by the Trust, CMS will, on or prior to the seventh calendar day succeeding the receipt of any such request for repurchase or redemption in good order, deposit any contingent deferred sales charge (“CDSC”) due the Distributor in its account with such bank as may from time to time be designated by the Distributor and pay to the shareholder from funds deposited by the Trust from time to time in the repurchase and redemption account maintained by CMS with its cash management bank, the appropriate repurchase or redemption price, as the case may be, as set forth in the Prospectus;

(b)If such certificate or request does not comply with said standards for repurchase or redemption as approved by the Trust, CMS will promptly notify the shareholder of such fact, together with the reason therefor, and shall effect such repurchase or redemption at the price in effect at the time of receipt of documents complying with said standards, or, in the case of a repurchase, at such other time as the Distributor, as agent for the Trust, shall so direct; and

(c)CMS shall notify the Trust and the Distributor as soon as practicable on each business day of the total number of Fund shares covered by requests for repurchase or redemption which were received by CMS in proper form on the previous business day, and shall notify the Distributor of deposits to its account with respect to any CDSC, such notification to be confirmed in writing.

12.Exchanges and Transfers.  Upon receipt by CMS of a request to exchange Fund shares held in a shareholder’s account for shares of another Fund, CMS will verify that the exchange request is made by authorized means and will process a redemption and corresponding purchase of shares in accordance with the Trust’s redemption and purchase policies and in accordance with the redemption and purchase provisions of this Agreement.  Upon receipt by CMS of a request to transfer Fund shares, and receipt of a share certificate for transfer or an order for the transfer of uncertificated shares, in either case with such endorsements, instruments of assignment or evidence of succession as CMS may require and accompanied by payment of any applicable transfer taxes, and satisfaction of any conditions contained in the Trust’s Declaration of Trust, By-Laws, and Prospectus, CMS will record the transfer of ownership of such shares in the appropriate records and will process the transfer in accordance with the Trust’s transfer policies and will open an account for the transferee, if a new shareholder, in accordance with the provisions of this Agreement.

13.Systematic Withdrawal Plans.  CMS will administer systematic withdrawal plans pursuant to the provisions of withdrawal orders duly executed by shareholders and the relevant Fund’s Prospectus.  Payments upon such withdrawal orders shall be made by CMS from the appropriate account maintained by the Trust with the Custodian.  Prior to the payment date CMS will withdraw from a shareholder’s account and present for repurchase or redemption as many shares as shall be sufficient to make such withdrawal payment pursuant to the provisions of the shareholder’s withdrawal plan and the relevant Fund’s Prospectus.

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14.Letters of Intent and Other Plans.  CMS will process such letters of intent for investing in Fund shares as are provided for in the Prospectus, and CMS will act as escrow agent pursuant to the terms of such letters of intent duly executed by shareholders.  CMS will make appropriate deposits to the account of the Distributor for the adjustment of sales charges as therein provided and will currently report the same to the Distributor, it being understood, however, that computations of any adjustment of sales charge shall be the responsibility of the Distributor or the Trust.  CMS will process such accumulation plans, group programs and other plans or programs for investing in shares as are provided for in the Prospectus.  In connection with any such plan or program, and with withdrawal plans described in paragraph 13 hereof, CMS will act as plan agent for shareholders and in so acting shall not be the agent of the Trust.

15.Tax Returns and Reports.  CMS will prepare, file with the Internal Revenue Service and any other federal, state or local governmental agency which may require such filing, and, if required, mail to shareholders such returns for reporting dividends and distributions paid by the Funds as are required to be so prepared, filed and mailed by applicable laws, rules and regulations, and CMS will withhold such sums as are required to be withheld under applicable Federal and state income tax laws, rules and regulations.

16.Record Keeping.  CMS will maintain records, which at all times will be the property of the  Trust and available for inspection by the Trust and Distributor, showing for each shareholder’s account the following:

(a)Name, address and United States taxpayer identification or Social Security number, if provided (or amounts withheld with respect to dividends and distributions on shares if a taxpayer identification or Social Security number if not provided);

(b)Number of shares held and number of shares for which certificates have been issued;

(c)Historical information regarding the account of each shareholder, including dividends and distributions paid, if any, and the date and price for all transactions on a shareholder’s account;

(d)Any stop or restraining order placed against a shareholder’s account;

(e)Information with respect to withholdings of taxes on dividends paid to foreign accounts; and

(f)Any instruction as to letters of intent, record address, and any correspondence or instructions or privileges (such as a telephone exchange privilege), relating to the current maintenance of a shareholder’s account.

In addition, CMS will keep and maintain on behalf of the Trust all records which the Trust or CMS is required to keep and maintain pursuant to any applicable statute, rule or regulation, including without limitation, Rule 31(a)-1 under the Investment Company Act of 1940, relating to the maintenance of records in connection with the services to be provided hereunder.  CMS shall be obligated to maintain at its expense only those records necessary to

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carry out its duties hereunder and the remaining records will be preserved at the Trust’s expense for the periods prescribed by law.

17.Other Information Furnished.  CMS will furnish to the Trust and the Distributor such other information, including shareholder lists and statistical information as may be agreed upon from time to time between CMS and the Trust.  CMS shall notify the Trust of any request or demand to inspect the share records books of the Trust and will act upon the instructions of the Trust as to permitting or refusing such inspection.

18.Shareholder Inquiries.  CMS will respond promptly to written correspondence from shareholders, registered representatives of broker-dealers engaged in selling Fund shares, the Trust and the Distributor relating to its duties hereunder, and such other correspondence as may from time to time be mutually agreed upon between CMS and the Trust.  CMS also will respond to telephone inquiries from shareholders with respect to existing accounts.

19.Communications to Shareholders and Meetings.  CMS will determine all shareholders entitled to receive, and will address and mail, all communications by the Trust to its shareholders, including quarterly and annual reports to shareholders, proxy material for meetings of shareholders and periodic communications to shareholders.  CMS will receive, examine and tabulate return proxy cards for meetings of shareholders and certify the vote to the Trust.

20.Insurance.  CMS will not reduce or allow to lapse any of its insurance coverage from time to time in effect, including but not limited to Errors and Omissions, Fidelity Bond and Electronic Data Processing coverage, without the prior written consent of the Trust.

21.Duty of Care and Indemnification.  CMS will at all times use reasonable care and act in good faith in performing its duties hereunder.  CMS will not be liable or responsible for delays or errors by reason of circumstances beyond its control, including without limitation, acts of civil or military authority, national or state emergencies, labor difficulties, fire, mechanical breakdown, flood or catastrophe, acts of God, insurrection, war, riots or failure of transportation, communication or power supply.

CMS may rely on certifications of the Secretary, any Assistant Secretary, the President, any Vice President, the Treasurer or any Assistant Treasurer of the Trust as to proceedings or facts in connection with any action taken by the shareholders or Trustees of that Trust, and upon instructions not inconsistent with this Agreement from the President, any Vice President, the Treasurer or any Assistant Treasurer of that Trust.  CMS may apply to counsel for the Trust, at the Trust’s expense, or its own counsel for advice whenever it deems expedient.  With respect to any action reasonably taken on the basis of such certifications or instructions or in accordance with the advice of counsel for instructions or in accordance with the advice of counsel for the Trust, the Trust will indemnify and hold harmless CMS from any and all losses, claims, damages, liabilities and expenses (including reasonable counsel fees and expenses).

The Trust will indemnify CMS against and hold CMS harmless from any and all losses, claims, damages, liabilities and expenses (including reasonable counsel fees and expenses) in respect to any claim, demand, action or suit not resulting from CMS’s bad faith or negligence and arising out of, or in connection with, its duties on behalf of the Trust under this Agreement.

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CMS shall also be indemnified and held harmless by the Trust against any loss, claim, damage, liability and expenses (including reasonable counsel fees and expenses) by reason of any act done by it in good faith and in reliance upon any instrument or certificate for shares believed by it (a) to be genuine and (b) to be signed, countersigned or executed by any person or persons authorized to sign, countersign, or execute such instrument or certificate.

CMS shall indemnify the Trust against and hold the Trust harmless from any and all losses, claims, damages, liabilities and expenses (including reasonable counsel fees and expenses) in respect of any claim, demand, action or suit resulting from CMS’s bad faith or negligence and arising out of, or in connection with, its duties on behalf of the Trust under this Agreement.

In any case in which a party to this Agreement may be asked to indemnify or hold harmless the other party hereto, the party seeking indemnification shall advise the other party of all pertinent facts concerning the situation giving rise to the claim or potential claim for indemnification, and each party shall use reasonable care to identify and notify the other promptly concerning any situation which presents or appears likely to present a claim for indemnification.

22.Employees.  CMS is responsible for the employment, control and conduct of its agents and employees and for injury to such agents or employees or to others caused by such agents or employees.  CMS assumes full responsibility for its agents and employees under applicable statutes and agrees to pay all employer taxes thereunder.

CMS shall maintain at its own expense insurance against public liability in a reasonable amount.

23.Anti-Money Laundering Program.  CMSI represents, warrants and covenants to the Trust that:

(a)it has established and maintains, and will continue to maintain and operate, an anti-money laundering program and/or procedures (including the Trust’s customer identification program) in accordance with all applicable laws, rules and regulations of its own jurisdiction including, where applicable, the Bank Secrecy Act (as amended by the USA PATRIOT Act of 2001 (the “Act”)).   CMSI further represents that it will adopt appropriate policies, procedures and internal controls to be fully compliant with any additional laws, rules or regulations, including the Act, to which it may become subject, including compliance with the rules recently adopted by the Treasury Department regarding foreign financial institutions that became effective July 5, 2006;

(b)it applies, and will continue to apply, its anti-money laundering program and/or procedures to all customers/investors of the Funds, and will take appropriate steps in accordance with the laws of its own jurisdiction to ensure that all relevant documentation is retained, as required, including identification relating to those customers/investors;

(c)it will provide an annual certification to the Trust confirming that it has implemented an anti-money laundering program and/or procedures as described in paragraph (a), and that it has performed, and intends to continue to perform, the requirements of the Trust’s

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Customer Identification Procedures.  CMSI will provide to the Trust periodic reports on the implementation of the anti-money laundering program and its ability to monitor the program;

(d)it complies with the United States regulations imposed by the Treasury Departments’ Office of Foreign Assets Control (“OFAC”), including but not limited to, the International Emergency Economic Powers Act, 50 U.S.C. §1701 et seq., The Trading with the Enemy Act, 50 U.S.C. App. 1 et seq., and any Executive Orders or regulations promulgated thereunder, which prohibit, among other things, the engagement in transactions with, holding the securities of, and the provision of services to certain embargoed foreign countries and specially designated nationals, specially designated narcotics traffickers, terrorist sanctions, and other blocked parties;

(e)it does not believe, has no current reason to believe and will notify the Trust immediately if it comes to have reason to believe that any shareholder of any Fund is engaged in money-laundering activities or is associated with any terrorist or other individual, entity or organization sanctioned by the United States or the jurisdictions in which it does business, or appear on any lists of prohibited persons, entities, and jurisdictions maintained and administered by OFAC; and

(f)if it has delegated to any third party or parties any of its tasks under its agreement with the Trust, CMSI has secured from that third party such representations, warranties and undertakings as are necessary to permit CMSI to provide the representations, warranties and covenants as are set forth in subparagraphs (a)-(e) above.

24.Termination.  This Agreement shall continue indefinitely until terminated (with respect to that Trust) by not less than ninety (90) days’ written notice given by the Trust to CMS or, by six (6) months written notice given by CMS to the Trust.  Upon termination hereof, the relevant Trust shall pay such compensation as may be due to CMS as of the date of such termination.

25.Successors.  In the event that (i) in connection with termination of this Agreement a successor to any of CMS’s duties or responsibilities hereunder is designated by the Trust by written notice to CMS, or (ii) CMA exercises its prerogative under paragraph 1 hereof to assume the duties and functions of CMS hereunder, CMS shall promptly, at the expense of the Trust (in the case of an event described in (i) above), transfer to such successor or CMA, as the case may be, a certified list of the shareholders of the Funds (with name, address and taxpayer identification or Social Security number), and historical record of the account of each shareholder and the status thereof, all other relevant books, records, correspondence and other data established or maintained by CMS under this Agreement in form reasonably acceptable to the Trust (if such form differs from the form in which CMS has maintained the same, the Trust shall pay any expenses associated with transferring the same to such form), and will cooperate in the transfer of such duties and responsibilities, including provision for assistance from CMS’s personnel in the establishment of books, records and other data by such successor or CMA.  CMS shall, in the case of an event described in (i) above, be entitled to reasonable compensation and reimbursement of its out-of-pocket expenses in respect of assistance provided in accordance with the preceding sentence.  Also, in the event of the termination of this Agreement, to the

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extent permitted by the agreements or licenses described below, CMS and CMA shall, if requested by the Trustees of the Trust, assign to any entity wholly owned, directly or indirectly, by Columbia Management Group, LLC (or its successors) or by the Trust, or any of them, all of their rights under any existing agreements to which either of them is a party and pursuant to which either has a right to have access to data processing capability in connection with the services contemplated by this Agreement and under any licenses to use third-party software in connection with the services contemplated by this Agreement and under any licenses to use third-party software in connection therewith, and in connection with such assignment shall grant to the assignee an irrevocable right and license or sublicenses, on a non-exclusive basis, to use any software used in connection therewith and, on an exclusive basis, any proprietary rights or interest which it has under such agreements or licenses.

26.Use of Affiliated Companies and Subcontractors.  In connection with the services to be provided by CMS or CMA under this Agreement, either CMS or CMA may, to the extent it deems appropriate, and subject to compliance with the requirements of applicable laws and regulations and upon receipt of approval of the Trustees, make use of (i) its affiliated companies and their directors, trustees, officers and employees and (ii) subcontractors selected by it, provided that it shall supervise and remain fully responsible for the services of all such third parties in accordance with and to the extent provided in this Agreement.  All costs and expenses associated with services provided by any such third parties shall be borne by CMS, CMA or such parties, except to the extent specifically provided otherwise in this Agreement.

27.Confidentiality.  Each of CMS and CMA agrees on behalf of itself and its employees to treat confidentially and as proprietary information of the Trust all records and other information relative to the Trust and its prior, present or potential shareholders and not to use such records and information for any purpose other than performance of its responsibilities and duties under this Agreement, except after prior notification to and approval in writing by the Trust, which approval shall not be unreasonably withheld and may not be withheld where CMS or CMA may be exposed to civil or criminal contempt proceedings for failure to comply, when requested to divulge such information by duly constituted authorities or when so requested by the Trust.

28.Compliance.  Each of CMS and CMA agree to comply with all applicable federal, state and local laws and regulations, codes, orders and government rules in the performance of its duties under this Agreement.  Each of CMS and CMA agree to provide the Trust with such certifications, reports and other information as the Trust may reasonably request from time to time to assist it in complying with, and monitoring for compliance with, applicable laws, rules and regulations (it being understood that such reports to be provided by CMSI to the Trust shall include the annual report of CMS pursuant to Rule 17Ad-13 under the Securities Exchange Act of 1934.)

29.Miscellaneous.  This Agreement shall be construed in accordance with and governed by the laws of the Commonwealth of Massachusetts.

The captions in this Agreement are included for convenience of reference only and in no way define or limit any of the provisions of this Agreement or otherwise affect their construction or effect.  This Agreement may be executed simultaneously in two or more counterparts, each of

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which shall be deemed an original, but all of which taken together shall constitute one and the same instrument.

A copy of the Agreement and Declaration of Trust of the Trust is on file with the Secretary of the Commonwealth of Massachusetts, and notice is hereby given that this Agreement is executed on behalf of each of the Trust by an officer or Trustee of the Trust in his or her capacity as an officer or Trustee of the Trust and not individually and that the obligations of or arising out of this Agreement are not binding upon any of the Trustees, officers or shareholders individually but are binding only upon the assets and property of the Trust.  Furthermore, notice is given that the assets and liabilities of each series of the Trust is separate and distinct and that the obligations of or arising out of this Agreement with respect to the series of the Trust are several and not joint, and to the extent not otherwise reasonably allocated among such series by the Trustees of the Trust, shall be deemed to have been allocated in accordance with the relative net assets of such series, and CMS and CMA agree not to proceed against any series for the obligations of another series.

[The remainder of this page intentionally left blank.]

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IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be duly executed as of the date first above written.

COLUMBIA ACORN TRUST
By:
	Name:	Bruce H. Lauer
	Title:	Vice President, Secretary and Treasurer
COLUMBIA MANAGEMENT SERVICES, INC.
By:
	Name:	Stephen T. Welsh
	Title:
COLUMBIA MANAGEMENT ADVISORS, LLC
By:
	Name:		J. Kevin Connaughton
	Title:

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SCHEDULE A

Funds

Columbia Acorn Fund

Columbia Acorn International

Columbia Acorn USA

Columbia Acorn Select

Columbia Acorn International Select

Columbia Thermostat Fund

SCHEDULE B

Payments under the Agreement to CMS shall be made in the first two weeks of the month following the month in which a service is rendered or an expense incurred.

Each Fund shall pay to CMS for the services to be provided by CMS under the Agreement an amount equal to the sum of the following:

1.A per account fee as agreed to from time to time by the Fund and CMS; PLUS

2.The Fund’s Allocated Share of CMS Reimbursable Out-of-Pocket Expenses; PLUS

3.Sub-Transfer Agency Fees.

In addition, CMS shall be entitled to retain as additional compensation for its services all CMS revenues for fees for wire, telephone, and redemption orders, IRA trustee agent fees and account transcripts due CMS from shareholders of the Fund and interest (net of bank charges) earned with respect to balances in the accounts referred to in paragraph 2 of the Agreement.

All determinations hereunder shall be in accordance with generally accepted accounting principles and subject to audit by the Funds’ independent accountants.

Definitions

“Allocated Share” for any month means that percentage of CMS Reimbursable Out-of-Pocket Expenses which would be allocated to a Fund for such month in accordance with the methodology described below under the heading “Methodology of Allocating CMS Reimbursable Out-of-Pocket Expenses.”

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“CMS Reimbursable Out-of-Pocket Expenses” means (i) out-of-pocket expenses incurred on behalf of the Funds by CMS for stationery, forms, postage and similar items and those expenses identified as “Out-of-Pocket Expenses” below and (ii) networking account fees paid to dealer firms by CMS on shareholder accounts established or maintained pursuant to the National Securities Clearing Corporation’s networking system, which fees are approved by the Trustees from time to time.

“Sub-Transfer Agency Fees” means such fees and expenses paid by CMS or its affiliates to third-party dealer firms or transfer agents that maintain omnibus accounts with a Fund subject to any limitations on the amount payable by the Fund as may be agreed to from time to time by the Fund and CMS.

“Out-of-Pocket Expenses” also include, but are not limited to, the following items:

·Microfiche/microfilm production

·Magnetic media tapes and freight

·Printing costs, including certificates, envelopes, checks and stationery

·Postage bulk, pre-sort, ZIP+4, barcoding, first class direct pass through to the Trust

·Telephone and telecommunication costs, including all lease, maintenance and line costs

·Proxy solicitations, mailings and tabulations

·Daily & Distributions advice mailings

·Shipping, Certified and Overnight mail and insurance

·Year-end forms and mailings

·Duplicating services

·Courier services

·Record retention as required by the Trust, retrieval and destruction costs, including, but not limited to, exit fees charged by third party record keeping vendors

·Third party audit reviews

·Such other miscellaneous expenses reasonably incurred by CMS in performing its duties and responsibilities under this Agreement.

The Funds agree that postage and mailing expenses will be paid on the day of or prior to mailing as agreed with CMS.  In addition, the Funds will promptly reimburse CMS for any other unscheduled expenses incurred by CMS whenever the Funds and CMS mutually agree that such expenses are not otherwise properly borne by CMS as part of its duties under the Agreement.

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Methodology of Allocating CMS Reimbursable Out-of-Pocket Expenses

CMS Reimbursable Out-of-Pocket Expenses are allocated to the Funds as follows:

A.	Identifiable	Based on actual services performed and invoiced to a Fund.
B.	Unidentifiable	Allocation will be based on three evenly weighted factors.
		·              number of shareholder accounts
		·              number of transactions
		·              average assets

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EX-99.H.2

Exhibit 99.h.2

AMENDED AND RESTATED AGREEMENT
BETWEEN COLUMBIA ACORN TRUST
AND COLUMBIA MANAGEMENT GROUP, LLC

THIS AMENDED AND RESTATED AGREEMENT (“Agreement”), is hereby made on July 31, 2006 by and between Columbia Acorn Trust (the “Trust”), a business trust organized and existing under the laws of the Commonwealth of Massachusetts, on behalf of each of its portfolio series (each, a “Fund” and collectively, the “Funds”), and Columbia Management Group, LLC, a limited liability company organized and existing under the laws of the Commonwealth of Massachusetts (hereinafter called “CMG”), on behalf of Columbia Management Distributor, Inc. (“CMD”), Columbia Management Services, Inc. (“CMS”) (formerly Liberty Funds Services, Inc.), Columbia Wanger Asset Management, L.P. (“CWAM”) and Columbia Management Advisors, LLC (“CMA”).  CMD, CMS, CWAM and CMA are subsidiaries of CMG and are collectively referred to herein as the “Service Providers.”

WITNESSETH:

WHEREAS, CMD acts as the Funds’ underwriter pursuant to that certain Distribution Agreement dated August 22, 2005, as amended, between CMD and Funds (the “Distribution Agreement”);

WHEREAS, CMS acts as the Funds’ transfer agent pursuant to that certain Shareholders’ Servicing and Transfer Agent Agreement dated September 29, 2000, as amended, between CMS and the Trust (the “TA Agreement”);

WHEREAS, CWAM acts as the Funds’ investment adviser pursuant to that certain Amended and Restated Investment Advisory Agreement dated August 1, 2006 between CWAM and the Trust (the “Advisory Agreement”); and

WHEREAS, CMA acts as sub-administrator for the Funds pursuant to that certain Sub-administration Agreement dated November 16, 2004 and effective September 29, 2000 between the predecessor of CMA and CWAM (the “Sub-Administration Agreement,” and together with the Distribution Agreement, TA Agreement, Advisory Agreement and Sub-Administration Agreement, the “Agreements”);

NOW, THEREFORE, in consideration of the premises and the mutual promises hereinafter set forth, the parties hereto agree as follows:

CMG agrees to cooperate fully with any and all efforts by the Trust, its Chief Compliance Officer (the “Fund CCO”) and its board of trustees (the “Board”) to provide assurance to the Trust, the Fund CCO and the Board that it and each Service Provider have implemented effective compliance policies and procedures, as applicable, administered by competent personnel.  In providing such assurance, CMG agrees that it or the applicable Service Providers will with respect to the Funds specifically or to matters more generally, as applicable, that could reasonably be expected to have a material adverse impact on the ability of the Service Providers or CMG to operate an effective compliance program:

1)hold periodic meetings between CMG compliance personnel or its senior management and the Fund CCO, and provide to the Fund CCO periodic reports on Compliance matters relevant to each Service Provider;

2)provide to the Fund CCO, promptly upon receipt, copies of reviews, inspection reports, audit reports, periodic and special reports by regulatory bodies, consultants, and external as well as internal auditors relating to CMG’s and/or the Service Providers’ compliance with applicable law and regulations, including reports by any entity appointed to review compliance policies and procedures by virtue of any order entered by the Securities and Exchange Commission;

3)provide to the Fund CCO periodic reports regarding selling or revenue sharing agreements with fund intermediaries, and any other agreements, formal or informal, entered into by CMD, including agreements that contain terms materially different from the form of selling agreement previously approved by the Board;

4)inform the Fund CCO promptly of any material violation, or material weakness in the design or implementation, of CMG’s or the Service Providers’ policies and procedures, including, but not limited to, those governing money laundering, sales practices, frequent trading and late trading;

5)take appropriate steps to correct promptly any material violation, or material weakness in the design or implementation, of CMG’s or the Service Providers’ policies and procedures; it being understood that the Board in its discretion may engage a third party selected by the Board, to assess whether CMG or the Service Provider has adequately addressed the material violation or weakness previously identified (it being understood that CMG or such Service Provider, as applicable, shall pay the reasonable expenses of such third party if (i) the Board determines that CMG or such Service Provider has not promptly corrected such violation or weakness; (ii) the Trust provides CMG or such Service Provider with prior written notice of the proposed engagement that identifies the anticipated cost and estimated expenses of such engagement; and (iii) CMG consents to bearing such expenses, such consent not to be unreasonably withheld.);

6)provide to the Fund CCO a full description of any waiver granted by CMS or CMG from the frequent trading prohibitions imposed by the Funds;

7)provide to the Fund CCO promptly reports concerning CMD’s actions to suspend or limit the privileges of any entity with whom it has executed a Selling Agreement, and on-going efforts to seek to secure execution of appropriate certifications or revised Selling Agreements that ensure sales in conformity with the Funds’ prospectus limitations;

8)provide the Fund CCO with prompt notice of material changes in the policies and procedures of the Service Providers;

2

9)report to the Fund CCO promptly any investor complaint regarding the Trust, including complaints about the distribution, marketing, operation or management of the Trust, or any complaint arising from the purchase or redemption of Fund shares;

10)provide to the Fund CCO periodic reports from CMS: (a) regarding its implementation of Rule 22c-2; (b) reflecting its monitoring for and investigation of instances of possible frequent or late trading in the Fund shares; (c) regarding the imposition of required redemption fees; (d) regarding CMS’ efforts to implement appropriate internal controls such as aging and escalation procedures, to ensure timely management review and oversight of its policies and procedures;

11)provide to the Fund CCO periodic reports from CWAM or CMG with respect to soft dollar arrangements and fair valuation of portfolio securities;

12)provide to the Fund CCO periodic reports from CWAM or CMG regarding stale prices of securities or fair valuation methodologies for foreign securities; and

13)hire, train and maintain sufficient compliance staff to implement effectively its policies and procedures, and to provide the Fund CCO with information about its staffing efforts.

During the periodic meetings referenced in paragraph 1 above, the Fund CCO and CMG compliance personnel may discuss any concerns regarding the frequency and scope of any required reports previously provided or actions previously undertaken pursuant to this Agreement.

CMG represents that the actions outlined in the Memorandum to the Fund CCO dated June 27, 2006 (the “June 27, 2006 Memorandum”) provided in response to the Columbia Acorn Trust — 2005 Annual Report of the Chief Compliance Officer dated May 23, 2006 (the Annual Report”) have been taken, and that CMG believes those actions together with the compliance program of CMG and such Service Providers  adequately remedy the weaknesses identified in the Annual Report with respect to CMG, CMS and CMA, subject to certain limitations  identified in writing to the Fund CCO and the Board and set forth in Exhibit D to the June 27, 2006 Memorandum.

In the event that the Trust determines that CMG or any of the Service Providers has materially breached the terms of this Agreement, the Trust may in its discretion suspend any and all payments to a Service Provider under the terms of the applicable agreement between the Trust and the Service Provider (such agreements listed on Appendix A hereto) if such material breach is not cured promptly following written notice to CMG or any of the Service Providers of such material breach.  If CMG or a Service Provider fails to or refuses to cure such material breach promptly after receiving notice of such material breach, and if the Trust otherwise determines to terminate the applicable agreement between the Trust and the Service Provider in accordance with the terms of that agreement, CMG or the Service Provider will pay all fees and expenses incurred by the Funds and their board in connection with finding a replacement Service Provider for the Trust.

3

COLUMBIA MANAGEMENT GROUP, LLC, on behalf of each of Columbia Management Distributor, Inc., Columbia Management Services, Inc., Columbia Wanger Asset Management, L.P., and Columbia Management Advisors, LLC
By:	/s/ Keith Banks
	Keith Banks
COLUMBIA ACORN TRUST
By:	/s/ Charles P. McQuaid
	Charles P. McQuaid
	President

4

Appendix A

Amended and Restated Investment Advisory Agreement between Columbia Acorn Trust and Columbia Wanger Asset Management, L.P. dated August 1, 2006

Amended and Restated Administration Agreement between Columbia Acorn Trust (on behalf of Columbia Acorn Fund, Columbia Acorn International, Columbia Acorn USA, Columbia Acorn Select, Columbia Acorn International Select and Columbia Thermostat Fund) and Columbia Wanger Asset Management, L.P. dated August 1, 2004

Distribution Agreement, as amended, between Columbia Acorn Trust and Columbia Management Distributor, Inc. dated August 22, 2005

Shareholders’ Servicing and Transfer Agent Agreement dated September 29, 2000, as amended, between Columbia Acorn Trust and Liberty Funds Services, Inc.

5

EX-99.H.3

	227 West Monroe, Suite 3000 Chicago, Illinois 60606 Tel. (312) 634-9200

As of May 1, 2007

Columbia Acorn Trust
227 W. Monroe Street
Suite 3300
Chicago, Illinois 60606

Ladies and Gentlemen:

Columbia Wanger Asset Management, L.P. (“CWAM”) hereby contractually undertakes as of the date hereof as follows with respect to the series of Columbia Acorn Trust designated Columbia Thermostat Fund (the “Fund”):

CWAM will waive fees and reimburse certain expenses of the Fund, such that total Fund ordinary operating expenses (exclusive of distribution and service fees, interest and fees on borrowings, and expenses associated with the Fund’s investment in other investment companies) do not exceed the annual rate of 0.25% of average daily net assets of the Fund, which agreement will continue in effect through April 30, 2008.  Notwithstanding the foregoing, the limitations on total ordinary operating expenses set forth herein shall not apply to any class of shares of a Fund established after the effective date hereof.

Nothing contained herein modifies or in any way amends the terms of the Amended and Restated Expense Reimbursement Agreement between the Fund and CWAM dated August 1, 2003.

This undertaking shall be binding upon any successors and assigns of CWAM.

		Very truly yours,
		COLUMBIA WANGER ASSET MANAGEMENT, L.P.
		By	/s/ Bruce H. Lauer
Agreed and accepted by
COLUMBIA ACORN TRUST
on behalf of its series Columbia Thermostat Fund
By	/s/ Bruce H. Lauer

EX-99.H.5

Exhibit 99.h.5

AMENDMENT NO. 1 TO PARTICIPATION AGREEMENT
BETWEEN COLUMBIA ACORN TRUST, COLUMBIA MANAGEMENT DISTRIBUTORS, INC. AND
MERRILL LYNCH LIFE INSURANCE COMPANY

THIS AMENDMENT, effective as of the 1st  day of May, 2007, by and among Columbia Acorn Trust, a Massachusetts business trust corporation (the “Fund”), Columbia Management Distributors, Inc., a corporation organized and existing under the laws of the Commonwealth of Massachusetts (the “Underwriter”) and Merrill Lynch Life Insurance Company, an Arkansas life insurance company (the “Company”);

WITNESSETH:

WHEREAS, the Fund, the Underwriter and the Company heretofore entered into a Participation Agreement dated March 4, 2005, as amended (the “Agreement”), with regard to separate accounts established for variable life insurance and/or variable annuity contracts offered by the Company; and

WHEREAS, the Fund, the Underwriter, and the Company desire to amend Schedule B to the Agreement in accordance with the terms of the Agreement.

NOW, THEREFORE, in consideration of the above premises, the Fund, the Underwriter and the Company hereby agree:

1.     Amendment.

(a)    Schedule B to the Agreement is amended in its entirety and is replaced by the Schedule B attached hereto;

(b)    Article X Notices. of the Agreement is hereby amended as follows:

If to the Company:	Barry G. Skolnick, Esquire
	Senior Vice President & General Counsel
	1700 Merrill Lynch Drive, 3rd Floor
	Pennington, New Jersey 08534

2.     Effectiveness.  The revised Schedule B of the Agreement shall be effective as the date hereof.

3.     Continuation.  Except as set forth above, the Agreement shall remain in full force and effective in accordance with its terms.

4.     Counterparts.  This Amendment may be executed in one or more counterparts, each of which shall be deemed to be an original.

(Signatures located on following page)

IN WITNESS WHEREOF, the Fund, the Underwriter and the Company have caused the Amendment to be executed by their duly authorized officers effective as of the day and year first above written.

COLUMBIA ACORN TRUST		MERRILL LYNCH LIFE INSURANCE COMPANY
By:	/s/ Charles P. McQuaid	By:	/s/ Kirsty Lieberman
Name:	Charles P. McQuaid	Name:	Kirsty Lieberman
Title:	President	Title:	Vice President & Senior Counsel
Date:	March 26, 2007	Date:	3/30/07

COLUMBIA MANAGEMENT DISTRIBUTORS, INC.
By:	/s/ Michael A. Jones
Name:	Michael A. Jones
Title:	President
Date:	3/27/07

Schedule B

DESIGNATED PORTFOLIOS AND CLASSES

·Columbia Acorn USA – A shares

·Columbia Acorn International – A shares

EX-99.H.7

Exhibit-99.(h)(7)

AMENDMENT NO. 1 TO PARTICIPATION AGREEMENT

BETWEEN COLUMBIA ACORN TRUST, COLUMBIA MANAGEMENT DISTRIBUTORS, INC. AND

ML LIFE INSURANCE COMPANY OF NEW YORK

THIS AMENDMENT, effective as of 1st day of May, 2007, by and among Columbia Acorn Trust, a Massachusetts business trust (the “Fund”), and Columbia Management Distributors, Inc., a corporation organized and existing under the laws of the Commonwealth of Massachusetts (the “Underwriter”) and ML Life Insurance Company of New York, a New York life insurance company (the “Company”);

WITNESSETH:

WHEREAS, the Fund, the Underwriter and the Company heretofore entered into a Participation Agreement dated March 4, 2005, as amended (the “Agreement”), with regard to separate accounts established for variable life insurance and/or variable annuity contracts offered by the Company; and

WHEREAS, the Fund, the Underwriter, and the Company desire to amend Schedule B to the Agreement in accordance with the terms of the Agreement.

NOW, THEREFORE, in consideration of the above premises, the Fund, the Underwriter and the Company hereby agree:

1.Amendment.

(a)Schedule B to the Agreement is amended in its entirety and is replaced by the Schedule B attached hereto;

(b)Article X Notices. of the Agreement is hereby amended as follows:

If to the Company:Barry G. Skolnick, Esquire

Senior Vice President & General Counsel

1700 Merrill Lynch Drive, 3rd Floor

Pennington, New Jersey 08534

2.Effectiveness.  The revised Schedule B of the Agreement shall be effective as the date hereof.

3.Continuation.  Except as set forth above, the Agreement shall remain in full force and effective in accordance with its terms.

4.Counterparts.  This Amendment may be executed in one or more counterparts, each of which shall be deemed to be an original.

(Signatures located on following page)

IN WITNESS WHEREOF, the Fund, the Underwriter and the Company have caused the Amendment to be executed by their duly authorized officers effective as of the day and year first above written.

COLUMBIA ACORN TRUST		ML LIFE INSURANCE COMPANY OF NEW YORK
By:	/s/ Charles P. McQuaid	By:	/s/ Kirsty Lieberman
Name:	Charles P. McQuaid	Name:	Kirsty Lieberman
Title:	President	Title:	Vice President & Senior Counsel
Date:	March 26, 2007	Date:	3/30/07

COLUMBIA MANAGEMENT DISTRIBUTORS, INC.
By:	/s/ Michael A. Jones
Name:	Michael A. Jones
Title:	President
Date:	3/27/07

Schedule B

DESIGNATED PORTFOLIOS AND CLASSES

·      Columbia Acorn USA – A shares

·      Columbia Acorn International – A shares

EX-99.I

Exhibit 99.i

70 West Madison Street, Suite 3100
Chicago, Illinois 60602-4207
312.372.1121 · Fax 312.827.8000

April 30, 2007

As counsel for Columbia Acorn Trust (the “Registrant”), we consent to the incorporation by reference of our opinion dated September 24, 2002 for the Registrant’s series designated Columbia Acorn Fund (formerly designated Liberty Acorn Fund), Columbia Acorn International (formerly designated Liberty Acorn International), Columbia Acorn USA (formerly designated Liberty Acorn USA), Columbia Acorn Select (formerly designated Liberty Acorn Twenty), Columbia Acorn International Select (formerly designated Liberty Acorn Foreign Forty) and Columbia Thermostat Fund filed with the Registrant’s registration statement on Form N-1A on September 24, 2002 (Securities Act file no.  2-34223).

In giving this consent we do not admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act of 1933.

/s/ Bell, Boyd & Lloyd LLP

chicago · washington

EX-99.J

Exhibit 99.j

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We hereby consent to the incorporation by reference in this Registration Statement on Form N-1A of our reports dated February 13, 2007, relating to the financial statements and financial highlights which appear in the December 31, 2006 Annual Reports to the Shareholders of Columbia Acorn Trust, which are also incorporated by reference into the Registration Statement.  We also consent to the references to us under the captions “Financial Highlights” and “Independent Registered Public Accounting Firm” in such Registration Statement.

/s/ PricewaterhouseCoopers LLP

Chicago, Illinois

April 27, 2007

EX-99.M.1

Exhibit 99.m.1

Columbia Acorn Trust
Amended and Restated Rule 12b-1 Distribution Plan

Columbia Acorn Trust (the Trust) hereby adopts the following distribution plan (the Plan) pursuant to Rule 12b-1 (the Rule) under the Investment Company Act of 1940 (the Act) on behalf of each Fund in the Trust designated in Appendix I, for the purpose of providing personal service and/or the maintenance of shareholder accounts and to facilitate the distribution of shares of the Funds.  This Plan applies only to the Class A, Class B or Class C shares of each Fund.

I.Plan Applying to Class A, B and C Shares

Each Fund having Class A, B, or C shares shall pay a service fee at the annual rate of 0.25% of the net assets of its Class A, B, or C shares, and a distribution fee at the annual rate of 0.50% of the average daily net assets of its Class B shares and 0.75 % of the average daily net assets of its Class C shares.  Amounts payable under this paragraph are subject to any limitations on such amounts prescribed by applicable laws or rules.

II.Payments of Fees Under the Plan

Each Fund shall make all payments of service and distribution fees under this Plan to Columbia Management Distributors, Inc. (CMD) monthly, on the 20th day of each month or, if such day is not a business day, on the next business day thereafter.  No Fund shall pay, nor shall CMD be entitled to receive, any amount under this Plan if such payment would result in CMD receiving amounts in excess of those permitted by applicable law or by rules of the National Association of Securities Dealers, Inc.

III.Use of Fees

CMD may pay part or all of the service and distribution fees it receives from a Fund as commissions to financial service firms that sell Fund shares or as reimbursements to financial service firms or other entities that provide shareholder services to record or beneficial owners of shares (including third-party administrators of qualified plans).  This provision does not obligate CMD to make any such payments nor limit the use that CMD may make of the fees it receives.

IV.Reporting

CMD shall provide to the Trust’s Trustees, and the Trustees shall review, at least quarterly, reports setting forth all Plan expenditures, and the purposes for those expenditures.

V.Other Payments Authorized

Payments by the Trust to CMD and its affiliates other than as set forth in Section I which may be indirect financing of distribution costs of Class A, Class B, or Class C shares are authorized by this Plan.

VI.Effective Date

This Plan shall be effective on August 1, 2006.

VII.Continuation; Amendment; Termination

This Plan shall continue in effect with respect to Class A, Class B and Class C shares only so long as specifically approved for that class at least annually as provided in the Rule.  The Plan may not be amended to increase materially the service fee or distribution fee with respect to a class of shares without such shareholder approval as is required by the Rule and any applicable orders of the Securities and Exchange Commission, and all material amendments of the Plan must be approved in the manner described in the Rule.  The Plan may be terminated with respect to any class of shares at any time as provided in the Rule without payment of any penalty.  The continuance of the Plan shall be effective only if the selection and nomination of the Trust’s Trustees who are not interested persons (as defined under the Act) of the Trust is effected by such non-interested Trustees as required by the Rule.

Approved by the Trustees on July 18, 2006
By:	/s/ Robert E. Nason
	Robert E. Nason
	Chairman

2

APPENDIX I

Columbia Acorn Fund
Columbia Acorn International
Columbia Acorn USA
Columbia Acorn Select
Columbia Acorn International Select
Columbia Thermostat Fund

Dated August 1, 2006

I-1

EX-99.N

Exhibit 99.n

COLUMBIA ACORN TRUST

Amended and Restated Plan pursuant to Rule 18f-3(d)
under the Investment Company Act of 1940

Each Series (each a “Columbia Acorn Fund”) of Columbia Acorn Trust (the “Trust”) as set forth in Schedule I may from time to time issue one or more of the following classes of shares as authorized by the Board of Trustees and as provided for herein:  Class A shares, Class B shares, Class C shares and Class Z shares.  Each class is subject to such investment minimums and other conditions of eligibility as are set forth in the Trust’s prospectus and statement of additional information for shares of that class as from time to time in effect.  The differences in expenses among these classes of shares and the conversion and exchange features of each class of shares are set forth below.  These differences are subject to change, to the extent permitted by law and by the Declaration of Trust and By-laws of the Trust, by action of the Board of Trustees.  This Plan, as amended and restated, shall be effective as of August 1, 2006.

CLASS A SHARES

Class A shares of each Columbia Acorn Fund are offered at net asset value (“NAV”) plus the initial sales charges described in the Trust’s prospectus and statement of additional information for Class A shares as from time to time in effect.  Initial sales charges may not exceed 5.75%, and may be reduced or waived as permitted by Rule 22d-1 under the Investment Company Act of 1940 (the “1940 Act”) and as described in the Trust’s prospectus and statement of additional information for Class A shares from time to time in effect.

Class A shares bought without an initial sales charge in accounts aggregating up to $50 million at the time of purchase that are redeemed within 12 months of the time of purchase are subject to a contingent deferred sales charge (“CDSC”) of 1.00% of either the purchase price or the NAV of the shares at the time of redemption, whichever is less.  Subsequent Class A share purchases that bring the value of an account above $1 million (but less than $50 million) are subject to a CDSC if redeemed within 12 months of the date of purchase.  The 12-month period begins on the first day of the month in which the purchase was made.  For purposes of applying the CDSC, shares held for the longest period of time are considered to have been redeemed before later acquired shares.  The CDSC does not apply to retirement accounts purchasing through a fee-based program of a broker-dealer.  The CDSC may be reduced or waived in certain circumstances as permitted by Rule 6c-10 under the 1940 Act and as described in the Trust’s prospectus and statement of additional information for Class A shares as from time to time in effect.

Class A shares pay a service fee pursuant to a plan adopted pursuant to Rule 12b-1 under the 1940 Act (“12b-1 Plan”) as described in the Trust’s prospectus and statement of additional information for Class A shares as from time to time in effect.  Such fee may be in an amount up to but may not exceed 0.25% per annum of the average daily net assets attributable to such class.

I-1

Class A shares pay all transfer agency fees and expenses, and any other expenses, specifically allocable to Class A shares.

Class A shares of a Columbia Acorn Fund may be exchanged, at the holder’s option, for Class A shares (and in some cases, certain other classes) of any other fund (each, including each Columbia Acorn Fund, a “Columbia Fund” and together, “Columbia Funds”) distributed by Columbia Management Distributors, Inc. or its successor, which offers Class A shares, without the payment of a sales charge, except to the extent such an exchange is limited by the prospectus of the other Columbia Fund for Class A shares as from time to time in effect and except further that if Class A shares of any non-money market Columbia Fund are exchanged within five months after purchase for shares of another Columbia Fund with a higher sales charge, then the difference in sales charges must be paid on the exchange.

No CDSC shall be charged on the exchange of Class A shares of a Columbia Acorn Fund for Class A shares of another Columbia Fund.  If the Class A shares received in the exchange are subsequently redeemed, the amount of the CDSC, if any, will be determined by the schedule of the Columbia Fund in which the original investment was made, and the holding period for determining the CDSC will include the holding period of the shares exchanged.

CLASS B SHARES

Class B shares of each Columbia Acorn Fund are offered at NAV, without an initial sales charge.  Class B shares that are redeemed within the period of time after purchase (not more than 6 years) specified in the Trust’s prospectus and statement of additional information for Class B shares as from time to time in effect are subject to a CDSC of up to 5% of either the purchase price or the NAV of the shares at the time of redemption, whichever is less; such percentage may be lower for certain Columbia Acorn Funds and declines the longer the shares are held, all as described in the Trust’s prospectus and statement of additional information for Class B shares as from time to time in effect.  For purposes of applying the CDSC, shares held for the longest period of time are considered to have been redeemed before later acquired shares.  Class B shares purchased with reinvested distributions are not subject to a CDSC.  The CDSC may be reduced or waived in certain circumstances, as permitted by Rule 6c-10 under the 1940 Act and as described in the Trust’s prospectus and statement of additional information for Class B shares as from time to time in effect.

Class B shares pay distribution fees and service fees pursuant to a 12b-1 Plan as described in the Trust’s prospectus and statement of additional information for Class B shares as from time to time in effect.  Such fees may be in amounts up to but may not exceed, respectively, 0.50% and 0.25% per annum of the average daily net assets attributable to such class.

Class B shares pay all transfer agency fees and expenses, and any other expenses, specifically allocable to Class B shares.

Class B shares of a Columbia Acorn Fund automatically convert to Class A shares of the same Columbia Acorn Fund eight years after purchase, except that Class B shares purchased through the reinvestment of dividends and other distributions on Class B shares convert to Class A shares in the same percentage as the amount of Class B shares otherwise being converted.

I-2

Class B shares of a Columbia Acorn Fund may be exchanged, at the holder’s option, for Class B shares (and in some cases, certain other classes) of any other Columbia Fund offering Class B shares, except to the extent such an exchange is limited by the prospectus of the other Columbia Fund as from time to time in effect, without the payment of a CDSC.  The holding period for determining the CDSC and the conversion to Class A shares for the Class B shares received in the exchange will include the holding period of the shares exchanged.  If the Class B shares received in the exchange are subsequently redeemed, the amount of the CDSC, if any, will be determined by the schedule of the Columbia Fund in which the original investment was made.

CLASS C SHARES

Class C shares of each Columbia Acorn Fund are offered at NAV without an initial sales charge.  Class C shares that are redeemed within one year from purchase may be subject to a CDSC of 1% of either the purchase price or the NAV of the shares at the time of redemption, whichever is less.  Class C shares purchased with reinvested dividends or capital gain distributions are not subject to a CDSC.  The CDSC may be reduced or waived in certain circumstances as permitted by Rule 6c-10 under the 1940 Act and as described in the Trust’s prospectus and statement of additional information for Class C shares as from time to time in effect.

Class C shares pay distribution fees and service fees pursuant to a 12b-1 Plan as described in the Trust’s prospectus and statement of additional information for Class C shares as from time to time in effect.  Such fees may be in amounts up to but may not exceed, respectively, 0.75% and 0.25% per annum of the average daily net assets attributable to such class.

Class C shares pay all transfer agency fees and expenses, and any other expenses, specifically allocable to Class C shares.

Class C shares of a Columbia Acorn Fund may be exchanged, at the holder’s option, for Class C shares (and in some cases, certain other classes) of any other Columbia Fund offering Class C shares, except to the extent such an exchange is limited by the prospectus of the other Columbia Fund for Class C shares as from time to time in effect, without the payment of a CDSC.  If the Class C shares received in the exchange are subsequently redeemed, the amount of the CDSC, if any, will be determined by the schedule of the Columbia Fund in which the original investment was made, and the holding period for determining the CDSC will include the holding period of the shares exchanged.  Only one exchange of any Columbia Fund Class C shares may be made in any three-month period.  For this purpose, an exchange into a Columbia Fund and a prior or subsequent exchange out of a Columbia Fund constitute an “exchange.”

CLASS Z SHARES

Class Z shares of each Columbia Acorn Fund are offered at NAV, without an initial sales charge, 12b-1 fee or CDSC.  Class Z shares of a Columbia Acorn Fund may be exchanged, at the holder’s option, for Class Z shares of any other Columbia Fund offering Class Z shares or for Class A shares of any other Columbia Fund not offering Class Z shares and offering Class A shares, except to the extent such exchange is limited by the prospectus of the other Columbia Fund for Class Z shares as from time to time in effect, without the payment of a sales charge. 

I-3

Class Z shares pay all transfer agency fees and expenses, and any other expenses, specifically allocable to Class Z shares.

Approved by the Trustees on July 18, 2006
By:	/s/ Robert E. Nason
Robert E. Nason
Chairman

I-4

SCHEDULE I

Columbia Acorn Fund

Columbia Acorn International

Columbia Acorn USA

Columbia Acorn Select

Columbia Acorn International Select

Columbia Thermostat Fund

EX-99.P.1

Exhibit 99.p.1

CWAM Code of Ethics

Effective January 2, 2007

Overview			3
Part I - Statement of General Principles			4
A.		Compliance with the Spirit of the Code	5
B.		Federal Law Prohibits Fraudulent and Deceptive Acts	5
C.		Compliance with other CWAM and BAC Policies	6
D.		Contacts for Questions and Reporting Violations of this Code	6
E.		Training and Education	7
Part II - Prohibited Transactions and Activities			8
A.	Prohibited Transactions in Mutual Funds		8
1.	Short-Term Trading Prohibition		8
2.	Late Trading Prohibition		8
3.	Market Timing Prohibition		8
B.	Prohibited Transactions in Reportable Securities		9
1.	Client Conflict		9
2.	Fourteen Calendar Day Blackout Period		9
3.	IPOs and Limited Offerings		9
4.	Short-Term Trading (60 Calendar Days)		9
5.	Selling Short and Transactions Involving Certain Derivatives		10
6.	Bank of America Closed-end Funds		10
7.	Excessive Trading		10
C.	Other Prohibitions		11
1.	Disclosure of Nonpublic Information		11
2.	Restriction on Service as Officer or Director by Covered Persons		11
3.	Participation in Investment Clubs		11
4.	Additional Restrictions for Specific Sub-Groups		11
D.	Additional Trading Restrictions Applicable to Investment Persons		11
1.	IPOs and Limited Offerings		11
2.	Client Account Priority		12
3.	Trade Restrictions Pertaining to Portfolio Managers		12
4.	Trade Restrictions Pertaining to Analysts		13
5.	Gifts		13
E.	Exemptions		13
Part III - Pre-Clearance of Transactions			15
A.	General Requirement to Pre-clear		15
B.	Procedures		15
C.	Exemptions		15
Part IV - Administration and Reporting Requirements			16
A.	Annual Code Coverage Acknowledgment and Compliance Certification		16
B.	Reporting Requirements for Covered Persons		16
C.	Exceptions from the above Reporting Requirements		17
D.	Code Administration		17
Part V - Penalties for Non-Compliance			18
Appendix A - Beneficial Ownership			20
Appendix B - Definitions			22
Appendix C — Other CWAM and BAC Policies			25
Appendix D — Reportable Funds			26
Appendix E — Reporting Forms			30

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Overview

This Code of Ethics (the “Code”) covers a wide range of ethical conduct with a focus on obligations with respect to personal securities trading. You are obligated to comply with the terms of this Code, and thus you are a “Covered Person” for purposes of this Code, if you have been notified by the Compliance Department (“Compliance”) of Columbia Wanger Asset Management (“CWAM”) that this Code applies to you.

You will be notified by Compliance that this Code applies to you if you are a director, officer or employee of CWAM.

Bank of America (“BAC”) associates who are not employees of CWAM will be notified if this Code applies to them due to their status as a support partner of CWAM.

Certain Covered Persons, including but not limited to portfolio managers and research analysts, may also be designated by Compliance as “Investment Persons” and have heightened responsibility under this Code. Investment Persons are obligated to comply with all provisions of the Code applicable to Covered Persons and additional provisions applicable to Investment Persons. If you are registered with the National Association of Securities Dealers (“NASD”) you may have additional obligations not identified in this Code due to such registration.

If you believe you should have been notified by Compliance that this Code applies to you and have not been so notified, you are obligated to contact Compliance.

Certain provisions of this Code apply to securities you beneficially own, or securities that you intend to beneficially acquire. Beneficial Ownership is defined in Appendix A and includes, among other things, securities held by members of your immediate household.

Part I of this Code sets forth certain general principles relating to the Code. Part II identifies certain prohibited transactions and activities. Part III identifies your obligation to pre-clear your personal security transactions. Part IV identifies your reporting obligations with respect to your personal securities transactions and holdings. Part V sets forth sanctions for failure to comply with this Code.

The CWAM Code of Ethics Committee (the “Committee”) is responsible for enforcing compliance with this Code. Failure to comply with this Code may result in disciplinary action, including termination of employment.

This Code is intended to satisfy the requirements of Rule 204A-1 of the Investment Advisers Act of 1940 (the “Advisers Act”) and Rule 17j-1 of the Investment Company Act of 1940 (the “Investment Company Act”). In addition, this Code is intended to satisfy certain NASD requirements for registered personnel.

Terms used herein that are both capitalized and bolded have the meaning set forth in Appendix B.

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Part I

Part I - Statement of General Principles

Our relationship with our Clients is fiduciary in nature. A fiduciary has an affirmative duty of care, loyalty, honesty and good faith. A number of specific obligations flow from the fiduciary duty we owe to our Clients, including:

·To act solely in the best interests of Clients and to make full and fair disclosure of all material facts, particularly where CWAM’s interest may conflict with those of its Clients;

·To have a reasonable, independent basis for our investment advice;

·To ensure that our investment advice is suitable to the Client’s investment objectives, needs and circumstances;

·To refrain from effecting personal securities transactions inconsistent with our Clients’ interests;

·To obtain best execution for our Clients’ securities transactions;

·To refrain from favoring the interest of a particular Client over the interests of another Client;

·To keep all information about Clients (including former Clients) confidential, including the Client’s identity, Client’s securities holdings information, and other non-public information; and

·To exercise a high degree of care to ensure that adequate and accurate representations and other information is presented.

All Covered Persons are in a position of trust and that position of trust dictates that you act at all times with the utmost integrity, avoid any actual or potential conflict of interest (described below), and not otherwise abuse that position of trust. As a fiduciary, you are required to put the interests of our Clients before your personal interests. All Covered Persons have a fiduciary duty with respect to each and all of our Clients.

A conflict of interest is any situation that presents an incentive to act other than in the best interest of a Client. A conflict of interest may arise, for example, when a Covered Person engages in a transaction that potentially favors: (i) CWAM’s interests over a Client’s interest, (ii) an associate’s interest over a Client’s interest, or (iii) one Client’s interest over another Client’s interest.

CWAM has adopted various policies designed to prevent, or otherwise manage, conflicts of interest. To effectively manage conflicts of interest, all Covered Persons must seek to prevent conflicts of interest, including the appearance of a conflict. Covered Persons must be vigilant about circumstances that present a conflict of interest and immediately seek assistance from their manager or one of the other resources identified in Part I.D of this Code.

Independence in the investment decision-making process is paramount. All Covered Persons must avoid situations that might compromise or call into question their exercise of independent judgment in the interest of Clients. For example, Covered Persons should not take personal advantage of unusual or limited investment opportunities appropriate for Clients.

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The general principles discussed in this section govern all conduct, regardless of whether or not such conduct is also covered by more specific standards and procedures set forth in other sections of this Code.

A.Compliance with the Spirit of the Code

The Committee recognizes that sound, responsible personal securities investing is an appropriate activity when trading is not excessive in nature, when it is conducted consistent with the Code and when it does not cause any actual, potential or apparent conflict of interest.

The Committee will not tolerate personal securities trading activity that is inconsistent with duties to our Clients or that injures the reputation and professional standing of our organization. Technical compliance with the specific requirements of this Code will not insulate you from sanction should a review of your personal securities trades indicate breach of your duty of loyalty to a Client or otherwise pose harm to our organization’s reputation.

The Committee has the authority to grant written waivers of the provisions of this Code. It is expected that this authority will be exercised only in rare instances.

B.Federal Law Prohibits Fraudulent and Deceptive Acts

All Covered Persons are required to comply with all Federal Securities Laws, including but not limited to Rule 204A-1 of the Advisers Act, Rule 17j-1 of the Investment Company Act and the anti-fraud provisions of both the Advisers Act and Investment Company Act.

The Advisers Act makes it unlawful for any investment adviser, directly or indirectly, to employ any device, scheme or artifice to defraud any client or prospective client, or to engage in any transaction or practice that operates as a fraud or deceit on such persons.

The Investment Company Act makes it unlawful for any director, trustee, officer or employee of an investment adviser of an investment company, as well as certain other persons, in connection with the purchase or sale, directly or indirectly, by such person of a security held or to be acquired by the investment company:

1.	To employ any device, scheme or artifice to defraud the fund;
2.	To make to the fund any untrue statement of a material fact or omit to state to the fund a material fact necessary in order to make the statements made, in light of the circumstances under which they are made, not misleading;
3.	To engage in any act, practice, or course of business which operates or would operate as a fraud or deceit upon the fund; or
4.	To engage in any manipulative practice with respect to the fund.

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C.Compliance with other CWAM and BAC Policies

Compliance with this Code is in addition to your obligation to comply with other CWAM and BAC policies that may be applicable to you.

All Covered Persons who maintain personal investment accounts must comply with the Bank of America Global Wealth and Investment Management Associate Designated Brokerage Account Policy. Unless an exception has been granted, that policy requires Covered Persons to maintain their current and any new Associate Accounts with Banc of America Investment Services, Inc. (“BAI”) or Merrill Lynch. The policy is available on the CWAM intranet.

Covered Persons are subject to additional policies, including but not limited to the following (also set forth in Appendix C):

·CWAM Statement of Operations and Supervisory Procedures Manual

·CWAM Information Wall Policy

·CWAM Misuses of Material Nonpublic Information Policy

·CWAM Portfolio Holdings Disclosure Policy

·Bank of America Corporation Code of Ethics and General Policy on Insider Trading

·Bank of America Policy on Excessive Trading and Market Timing in the Bank of America Retirement Plans

·Bank of America Global Wealth and Investment Management Gifts and Hospitality Policy

D.Contacts for Questions and Reporting Violations of this Code

Each Covered Person must promptly report any conduct that he or she reasonably believes constitutes or may constitute a violation of the Code. Covered Persons must promptly report all relevant facts and circumstances relating to such potential violation of the Code to either the Chief Compliance Officer (“CCO”; currently, Joe LaPalm at 312-634-9829) or the Ethics and Compliance Helpline at 1-888-411-1744 (domestic) or 1-770-623-6334 (international). If you wish to remain anonymous, you may simply refer to yourself as a “BAC Associate.”  You will not be retaliated against for reporting information in good faith in accordance with this policy.

All questions, comments or concerns may be directed to Columbia Management’s Ombudsperson (currently, Kevin V. Waspat 212-893-7246).

In addition, if you have any questions relating to a personal securities transaction, you may call Compliance  directly or send an email to “DG 227w-Compliance Dept” and if you have any questions relating to the conflict of interest provisions of this Code, you may contact Joe LaPalm at 312-634-9829.

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E.Training and Education

Training on this Code will occur periodically. All Covered Persons are required to attend all assigned training sessions and read any applicable materials.

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Part II

Part II - Prohibited Transactions and Activities

Part II of the Code focuses on personal securities trading and identifies certain prohibited transactions and activities. In the event there is a stated exception to a prohibited transaction and you qualify for the exception, you are not relieved of any other obligation you may have under this Code, including any requirement to pre-clear (see Part III) and report (see Part IV) the transaction.

A.Prohibited Transactions in Mutual Funds

1.Short-Term Trading Prohibition.

No Covered Person may engage in the purchase and subsequent sale or exchange of the same class of shares of a Reportable Fund (an open-end mutual fund managed by Bank of America or its subsidiaries, except for money market and short-term bond funds, as listed in Appendix D) within 60 calendar days of one another. Funds held in a Bank of America 401(k) account or other retirement plan shall be subject to the short-term trading prohibitions of that plan. Therefore, if a Covered Person purchases shares of a Reportable Fund outside of a Bank of America retirement plan, he or she will not be permitted to sell or exchange any shares of that fund, including shares previously purchased, for at least 60 calendar days. The CCO has the authority to grant exceptions to the requirements of this section; however, such exceptions will be granted in only rare cases of hardship or other unusual circumstances.

2.Late Trading Prohibition.

Late Trading of mutual funds, wherein an order for mutual fund shares is placed after the fund is closed for the day and the transaction is priced using the closing price for that day, is illegal. No Covered Person shall engage in any such Late Trading transaction in mutual fund shares. In addition to being illegal, Late Trading presents a conflict of interest and a violation of fiduciary duty.

3.Market Timing Prohibition.

No Covered Person shall engage in mutual fund Market Timing activities. The Committee believes that the interests of a mutual fund’s long-term shareholders and the ability of a mutual fund to manage its investments may be adversely affected when fund shares are repeatedly bought, sold or exchanged by any individual or entity within short periods of time to take advantage of short-term differentials in the net asset values of such funds. This practice, known as Market Timing can occur in direct purchases and sales of mutual fund shares, through rapid reallocation of funds held in a 401(k) plan or similarly structured retirement plan or other accounts invested in mutual fund assets, or through the rapid reallocation of funds held in variable annuity and variable life policies invested in mutual fund assets. In addition to being prohibited by this Code, mutual fund Market Timing presents a conflict of interest and is a violation of fiduciary duty.

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B.Prohibited Transactions in Reportable Securities  

1.Client Conflict.

No Covered Person shall purchase or sell, directly or indirectly, any Reportable Security (all corporate securities, Closed-end Funds, and exchange traded funds, further defined in Appendix B)  in which such person had, or by reason of such transaction acquires, any direct or indirect Beneficial Ownership when, at the time of such purchase or sale, the Covered Person knew, or should have known, that the same class of security:

·is the subject of an open buy or sell order for a Client Account; or

·is Being Considered for Purchase or Sale by a Client Account.

2.Fourteen Calendar Day Blackout Period.

No Covered Person shall purchase or sell any Reportable Security within a period of seven calendar days before or after a purchase or sale of the same class of security by a Client Account. The spirit of this Code requires that no Covered Person intentionally delay trades on behalf of a Client Account so that their own personal trades avoid falling within the fourteen day blackout period.

3.IPOs and Limited Offerings.

No Covered Person shall acquire Beneficial Ownership of securities in an IPO or Limited Offering except with the prior written approval of the CCO. Covered Persons registered with the NASD are prohibited from investing in IPOs. Investment Persons may invest in IPOs but are subject to the additional restrictions outlined in Part II.D.1, below. In approving such acquisition, the CCO must determine that the acquisition does not conflict with the Code or its underlying policies, that the investment opportunity could not instead be reserved for Clients, and that the opportunity has not been offered to the Covered Person because of the Covered Person’s relationship with BAC or a Client. The CCO may approve acquisition under certain circumstances, such as:

·An opportunity to acquire securities of an insurance company converting from a mutual ownership structure to a stockholder ownership structure, if the Covered Person’s ownership of an insurance policy issued by the IPO company or an affiliate of the IPO company conveys the investment opportunity;

·An opportunity resulting from the Covered Person’s pre-existing ownership of an interest in the IPO company or status of an investor in the IPO company; or

·An opportunity made available to the Covered Person’s spouse, in circumstances permitting the CCO reasonably to determine that the opportunity is being made available for reasons other than the Covered Person’s relationship with BAC or its Clients (for example, because of the spouse’s employment).

4.Short-Term Trading (60 Calendar Days).

No Covered Person may profit from any purchase and sale of the same class of Reportable Security within any period of 60 calendar days or less. Note, regarding this restriction, that:

(a)The 60 calendar day restriction period commences the day after the purchase of any Reportable Security.

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(b)The 60-day restriction applies on a “last in, first out basis.”  As a result, a Covered Person (or Family/Household Member) may not buy and sell the same class of Reportable Security within 60 days even though the specific shares or other securities involved may have been held longer than 60 days, when doing so will result in a profit to the Covered Person.

(c)Purchase and sale transactions in the same security within 60 days that result in a loss to the Covered Person (or Family/Household Member) are not restricted.

(d)The 60-day restriction does not apply to the exercise of options to purchase shares of BAC stock and the immediate sale of the same or identical shares, including so-called “cashless exercise” transactions.

(e)Strategies involving corporate securities options with expirations of less than 60 days may result in violations of the short-term trading ban.

(f)Involuntary transactions that are the result of unforeseen corporate activity occurring within 60 days of purchase are not restricted.

(g)Exceptions to the short-term trading ban may be requested in writing, addressed to the CCO, in advance of a trade and will generally be granted only in rare cases of hardship, gifting of securities or other unusual circumstances where it is determined that no abuse is involved and the equities of the situation strongly support an exception to the ban. Circumstances that could provide the basis for an exception from short-term trading restriction might include, for example, among others:

·the disclosure of a previously nonpublic, material corporate, economic or political event or activity that could cause a reasonable person in like circumstances to sell a security even if originally purchased as a long-term investment; or

·the Covered Person’s economic circumstances materially change in such a manner that enforcement of the short-term trading ban would result in the Covered Person being subjected to an avoidable, inequitable economic hardship.

·An irrevocable charitable gift of securities provided no abuse is intended.

5.Selling Short and Transactions Involving Certain Derivatives

No Covered Person may sell short any Reportable Security; provided, however, that Covered Persons may sell short against broad market indexes and “against the box.”

No Covered Person may write a “naked” call option on any Reportable Security or purchase a put option on any Reportable Security; provided, however, that Covered Persons may write a covered call or buy a protective put on a Reportable Security.

6.Bank of America Closed-end Funds.

No Covered Person shall acquire Beneficial Ownership of securities of any Closed-end Fund advised by BAC except with the prior written approval of Compliance.

7.Excessive Trading.

Covered Persons are strongly discouraged from engaging in excessive trading for their personal accounts. Trading activity of Covered Persons that, by the sole determination of

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management, interferes with daily responsibilities is prohibited. Covered persons who are warned of excessive trading by Compliance must appropriately reduce trading activity or will be subject to disciplinary action.

C.Other Prohibitions

1.Disclosure of Nonpublic Information.

Covered Persons are prohibited from disclosing to persons outside of CWAM any material nonpublic information about any Client, the securities investments made on behalf of a Client, information about contemplated securities transactions, or information regarding our trading strategies, except as required to effectuate securities transactions on behalf of a Client or for other legitimate business purposes. Disclosure of nonpublic information is a breach of fiduciary duty.

2.Restriction on Service as Officer or Director by Covered Persons.

Covered Persons are prohibited from serving as an officer or director of any publicly traded company, other than Bank of America Corporation or its affiliates, absent prior authorization from Compliance based on a determination that the board service would not be inconsistent with the interests of any Client. A Covered Person serving as a director or officer of a private company may be required to resign, either immediately or at the end of the current term, if the company goes public during his or her term as director or officer.

3.Participation in Investment Clubs.

Covered Persons (including with respect to assets that are beneficially owned by the Covered Person) may participate in private investment clubs or other similar groups only upon advance written approval from Compliance, subject to such terms and conditions as Compliance may determine to impose. Investment Persons may not begin participation in private investment clubs or other similar groups.

4.Additional Restrictions for Specific Sub-Groups.

Specific sub-groups in the organization may be subject to additional restrictions, as determined by Compliance. Compliance shall keep separate applicable procedures and communicate accordingly to these groups.

D.Additional Trading Restrictions Applicable to Investment Persons

1.IPOs and Limited Offerings.

All Investment Persons are required to obtain written manager pre-approval for personal investments in IPOs and Limited Offerings. This means you are required to obtain approval from your immediate manager or their designee. After obtaining manager pre-approval, Investment Persons must obtain pre-approval from the CCO.

Investment Persons who have been authorized to acquire securities in a Limited Offering are required to disclose that investment to their manager when the Investment Person plays a role in any Client’s subsequent consideration of an investment in the issuer. In such circumstances, the decision to purchase securities of the issuer for the Client should be made

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either by another employee or, at a minimum, should be subject to an independent review by investment personnel with no personal interest in the issuer.

2.Client Account Priority

The Funds and Client Accounts under management shall be given priority when investment opportunities arise. Portfolio Managers and Analysts may not execute transactions for their personal accounts without first determining whether the transaction is appropriate for a Fund or Client Account.

Analysts at CWAM are assigned industry coverage areas. Portfolio Managers at CWAM are also assigned coverage areas, in addition to their overall responsibility for Funds and Client Accounts. All Portfolio Managers and Analysts must comply with the pre-clearance and reporting restrictions of this Code, and are, in addition, subject to the following restrictions. A security is “followed by CWAM” for purposes of this Section if it has been entered into CWAM’s Equity Research Data Base.

3.Trade Restrictions Pertaining to Portfolio Managers

(a)Purchases

i. Portfolio Managers may not purchase any securities owned by CWAM and within the coverage area of that Portfolio Manager, or not within the coverage area of that Portfolio Manager but held by the Funds or Client Accounts managed by the Portfolio Manager.

ii. Portfolio Managers may not purchase securities followed by CWAM and within the coverage area of that Portfolio Manager.

iii.Portfolio Managers may not purchase any security that is within the investment parameters established by the Funds or Client Accounts managed by the Portfolio Manager UNLESS:

·It is outside the Portfolio Manager’s coverage area;

·The Analyst responsible for that coverage area declines the investment opportunity on behalf of the Funds and Client Accounts advised by the Portfolio Manager; and

·The Analyst’s conclusion is provided in writing to Compliance in advance of the transaction.

(b)Sales

Absent a showing of hardship or other extraordinary circumstances, a Portfolio Manager who owns a security that is later purchased by the Fund or Client Accounts advised by that Portfolio Manager may not sell that security unless and until the Fund or Client Accounts completely dispose of that security.

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4.Trade Restrictions Pertaining to Analysts

(a)Purchases

i. Analysts may not purchase any security within their coverage areas that is owned by the Funds or Client Accounts.

ii. Analysts may not purchase any security within their coverage areas that is followed by CWAM.

iii. Analysts may not purchase any security within their coverage areas UNLESS:

·The investment is inappropriate for Funds or Client Accounts because it is not within their investment parameters or is otherwise unsuitable;

·The purchase is approved in advance and in writing by the CIO based on that person’s independent decision to decline the investment opportunity on the basis that the security is inappropriate for Funds or Client Accounts, or is otherwise unsuitable; and

·The Chief Investment Officer’s conclusion is provided in writing to Compliance in advance of the transaction.

(b)Sales

Absent a showing of hardship or other extraordinary circumstances, an Analyst who owns a security within his or her coverage area that is later purchased by the Fund or Client Accounts may not sell that security unless and until the Fund or Client Accounts completely dispose of that security.

5.Gifts

Notwithstanding the restrictions above, an Investment Person may make an irrevocable gift of securities to a charitable organization, provided any such gift is first approved by Compliance.

E.Exemptions

The following transactions are exempt from the prohibitions contained in this Part II:

·Transactions effected pursuant to an Automatic Investment Plan. Note this does not include transactions that override or otherwise depart from the pre-determined schedule or allocation features of the investment plan.

·Purchases effected upon the exercise of rights issued by an issuer pro rata to all holders of a class of its securities, to the extent such rights were acquired from such issuer, and sales of such rights so acquired.

·Transactions that are involuntary on the part of the Covered Person (e.g., stock splits and automatic conversions including redemptions, mergers and acquisitions).

·Transactions effected in any account in which the Covered Person may have a beneficial interest, but no direct or indirect Influence or Control of investment or

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trading activity, such as a blind trust or third-party advised discretionary account. Accounts managed by another Covered Person do not qualify for this exemption.

·Securities issued by BAC; provided, however, that this exemption does not apply to BAC securities purchased in a Limited Offering. BAC securities are subject to the short-term trading provisions of this Code and the standards of conduct and liability discussed in the Bank of America Corporation’s General Policy on Insider Trading.

·Such other transactions as the Committee shall approve in their sole discretion, provided that Compliance shall find that such transactions are consistent with the Statement of General Principles of this Code and applicable law. The Committee shall maintain a record of the approval and will communicate to the Covered Person’s manager(s).

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Part III

Part III - - Pre-Clearance of Transactions

A.General Requirement to Pre-clear

Covered Persons must pre-clear all transactions in Reportable Securities in which they have, or intend to acquire, Beneficial Ownership using the appropriate pre-clearance procedures. In addition, Covered Persons must pre-clear all redemptions or exchanges of Reportable Funds.

B.Procedures

In order to pre-clear a transaction, Covered Persons shall email CWAM Compliance with the request, specifying the Reportable Security or Reportable Fund, and shall not effect a trade until approval is granted by CWAM Compliance. Pre-clearance requests will be considered during New York Stock Exchange hours; requests submitted after the close of trading will be considered the following business day. Pre-clearance approvals are valid until 3:00 pm central time of the next business day after approval. For example, if a pre-clearance approval is granted on Tuesday, the approval is valid until 3:00 pm central time Wednesday.

C.Exemptions

The following transactions are exempt from the pre-clearance requirement:

·Transactions in BAC Retirement Plans

·Transactions in Company-Directed 401(k) Plans (provided they do not hold Reportable Funds or Reportable Securities)

·Transactions in 529 Plans

·Transactions by Covered Persons on leave that do not have home access to CWAM’s data; provided, however, that transactions by Covered Persons on leave with home access are not exempt from the pre-clearance requirements.

·Transactions effected in any account in which the Covered Person may have a beneficial interest, but no direct or indirect Influence or Control of investment or trading activity, such as a blind trust or third-party advised discretionary account. Accounts managed by another Covered Person do not qualify for this exemption.

·Transactions effected pursuant to an Automatic Investment Plan. Note this does not include transactions that override or otherwise depart from the pre-determined schedule or allocation features of the investment plan.

·Purchases effected upon the exercise of rights issued by an issuer pro rata to all holders of a class of its securities, to the extent such rights were acquired from such issuer, and sales of such rights so acquired.

·Transactions that are involuntary on the part of the Covered Person (e.g., stock splits, automatic conversions).

·Such other transactions as the Committee shall approve in their sole discretion, provided that Compliance shall find that such transactions are consistent with the Statement of General Principles of this Code and applicable law. The Committee shall maintain a record of the approval and will communicate to the Covered Person’s manager(s).

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Part IV

Part IV - Administration and  Reporting Requirements

A.Annual Code Coverage Acknowledgment and Compliance Certification

All Covered Persons will annually furnish acknowledgment of coverage (including Family/Household Members) under, and certification of compliance with, this Code. Copies of this Code and any amendments to the Code are required to be provided to all Covered Persons. All Covered Persons are required to provide acknowledgment of their receipt of the Code and any amendments.

B.Reporting Requirements for Covered Persons

You must report holdings of you and your Family/Household Members of Reportable Securities and Reportable Funds.

You must also report accounts in which you or any Family/Household Member have direct or indirect ownership interest that are capable of holding Reportable Securities or Reportable Funds, including accounts such as those with broker-dealers, banks, fund companies and insurance companies (“Investment Accounts”). Therefore, even if an Investment Account does not currently contain Reportable Securities or Reportable Funds, you are obligated to report the existence of such Investment Account if it has the capacity to hold such securities.

The information you report regarding your Investment Accounts and holdings of Reportable Securities and Reportable Funds must not be more than 45 days old. Such reporting is required as follows:

·By the 10th calendar day after becoming a Covered Person, you must report such holdings, acknowledge that you have read and understand this Code, that you understand that it applies to you and to your Family/Household Members and that you understand that you are a Covered Person (and, if applicable, an Investment Person) under the Code (Form A).

·By the 30th calendar day following the end of the calendar quarter, all Covered Persons are required to provide Compliance with a report of their Investment Accounts (including Investment Accounts opened during the quarter) and all transactions, whether automatic or voluntary, in Reportable Securities and Reportable Funds during the quarter (Form B).

·By the 30th calendar day after the end of the calendar year, Covered Persons are required to provide Compliance with a detailed annual report of their holdings of any Reportable Securities and Reportable Funds (Form C).

Each Covered Person shall cause every broker-dealer or investment services provider with whom he or she (or a Family/Household Member) maintains an Investment Account to provide duplicate periodic statements and trade confirmations to Compliance for all accounts holding or transacting trades in Reportable Securities or Reportable Funds. All duplicate statements and confirmations should be sent to the following address:

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Compliance Department

Columbia Wanger Asset Management

227 W. Monroe Street, Suite 3000

Chicago, IL 60606

C.Exceptions from the above Reporting Requirements

Covered Persons on leave who do not have home access will be exempt from the above reporting requirements while on leave. Covered Persons on leave with home access will be responsible for the above reporting.

The following Investment Accounts do not need to be reported, and therefore transactions within these accounts also do not need to be reported:

·BAC Retirement Plans

·Company-Directed 401(k) Plans (provided they  are not capable of holding any Reportable Funds or Reportable Securities)

·529 Plans

·Accounts in which a Covered Person has Beneficial Ownership but not investment discretion, Influence or Control, such as a blind trust or third-party advised discretionary account. Accounts managed by another Covered Person do not qualify for this exemption.

D.Code Administration

The Committee has charged Compliance with the responsibility of day-to-day administration of this Code. Compliance will quarterly provide reports to the Committee that will include all material violations noted during the period. The quarterly report will include associate name, job title, manager name, description of the violation, and a record of any recommended sanction.

The CCO shall report any relevant issues to the respective Fund CCO and mutual fund board of trustees as required by Rule 17j-1 of the Investment Company Act and such fund’s code of ethics.

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Part V

Part V - Penalties for Non-Compliance

Upon discovering a violation of the Code, Compliance shall take whatever remedial steps it deems necessary and available to correct an actual or apparent conflict (e.g., trade reversal, etc.). Following those corrective efforts, the Committee may impose sanctions if, based upon all of the facts and circumstances considered, such action is deemed appropriate. The magnitude of these penalties varies with the severity of the violation, although repeat offenders will likely be subjected to harsher punishment. It is important to note that violations of the Code may occur without employee fault (e.g., despite pre-clearance). In those cases, punitive action may not be warranted, although remedial steps may still be necessary. Violations of the Code include, but are not limited to the following:

·Execution of a personal securities transaction without pre-clearance;

·Execution of a personal securities transaction with pre-clearance, but Client account activity in the same issuer occurs within seven days of the employee’s personal securities transaction;

·Execution of a personal securities transaction after being denied approval;

·Profiting from short-term trading of Reportable Securities (60 calendar days);

·Trading Reportable Funds in violation of the 60 day restriction;

·Failure to disclose the opening or existence of an Investment Account;

·Failure to obtain prior approval of a purchase of an IPO or shares in a Limited Offering; and

·Failure to timely complete and return periodic certifications and acknowledgments.

The Committee will consider the specific facts and circumstances of any violations and will determine appropriate sanctions. Factors to be considered during any review would include but are not limited to:

·Whether the act or omission was intentional or voluntary;

·Whether mitigating or aggravating factors existed;

·The person’s history or prior violations of the Code;

·The person’s cooperation, acknowledgment of transgression and demonstrable remorse;

·The person’s position within the firm (i.e., whether the employee is deemed to be a Covered Person or Investment Person);

·Whether the person transacted in the security of an issuer in which his/her product area has invested or could invest;

·Whether the person was aware of any information concerning an actual or contemplated investment in that same issuer for any Client account; and

·Whether the price at which the personal securities transaction was effected was more advantageous than the price at which the Client transaction in question was effected.

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The type of sanctions to be imposed include, but are not limited to, oral or written warnings, trade reversals, disgorgement of profits, monetary fines, suspension or termination of personal trading privileges and employment suspension or termination.

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Appendix A - Beneficial Ownership

For purposes of the Code, the term “Beneficial Ownership” shall be interpreted in accordance with the definition of “beneficial owner” set forth in Rule 16a-l(a)(2) under the Securities Exchange Act of 1934, as amended, which states that the term “beneficial owner” means “any person who, directly or indirectly, through any contract, arrangement, understanding, relationship or otherwise, has or shares a direct or indirect pecuniary interest in a security.”  The term “pecuniary interest” is further defined to mean “the opportunity, directly or indirectly, to profit or share in any profit derived from a transaction in the subject securities.”

The pecuniary interest standard looks beyond the record owner of securities. As a result, the definition of Beneficial Ownership is very broad and encompasses many situations that might not ordinarily be thought to confer a “pecuniary interest” in or “beneficial ownership” of securities.

Securities Deemed to be “Beneficially Owned”

Securities owned “beneficially” would include not only securities held by you for your own benefit, but also securities held (regardless of whether or how they are registered) by others for your benefit in an account over which you have Influence or Control, such as securities held for you by custodians, brokers, relatives, executors, administrators, or trustees. The term also includes securities held for your account by pledgees, securities owned by a partnership in which you are a general partner, and securities owned by any corporation that you control.

Set forth below are some examples of how Beneficial Ownership may arise in different contexts.

·Family Holdings. Securities held by members of your immediate family sharing the same household with you (“Family/Household Member”) are presumed to be beneficially owned by you. Your “immediate family” includes any child, stepchild, grandchild, parent, stepparent, grandparent, spouse, significant other, sibling, mother-in-law, father-in-law, son-in-law, daughter-in-law, brother-in-law, or sister-in-law (but does not include aunts and uncles, or nieces and nephews). The definition also includes adoptive relationships. You may also be deemed to be the beneficial owner of securities held by an immediate family member not living in your household if the family member is economically dependent upon you.

·Partnership and Corporate Holdings. A general partner of a general or limited partnership will generally be deemed to beneficially own securities held by the partnership, as long as the partner has direct or indirect Influence or Control over the management and affairs of the partnership. A limited partner will generally not be deemed to beneficially own securities held by a limited partnership, provided he or she does not own a controlling voting interest in the partnership. If a corporation is your “alter ego” or “personal holding company”, the corporation’s holdings of securities are attributable to you.

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·Trusts. Securities held by a trust of which you are a beneficiary and over which you have any direct or indirect Influence or Control would be deemed to be beneficially owned by you. An example would be where you as settlor have the power to revoke the trust without the consent of another person, or have or share investment control over the trust.

·Estates. Ordinarily, the term “Beneficial Ownership” would not include securities held by executors or administrators in estates in which you are a legatee or beneficiary unless there is a specific bequest to you of such securities, or you are the sole legatee or beneficiary and there are other assets in the estate sufficient to pay debts ranking ahead of such bequest.

Securities Deemed Not to be “Beneficially Owned”

For purposes of the Code, the term “Beneficial Ownership” excludes securities or securities accounts held by you for the benefit of someone else if you do not have a pecuniary interest in such securities or accounts. For example, securities held by a trust would not be considered beneficially owned by you if neither you nor an immediate family member is a beneficiary of the trust. Another example illustrating the absence of pecuniary interest, and therefore also of Beneficial Ownership, would be securities held by an immediate family member not living in the same household with you, and who is not economically dependent upon you.

“Influence or Control”

Transactions/Accounts over which neither you nor any other Covered Person have “any direct or indirect influence or control” are not subject to the trading restrictions in Parts II and III or reporting requirements in Part IV of the Code. To have Influence or Control, you must have an ability to prompt, induce or otherwise effect transactions in the account. Like Beneficial Ownership, the concept of Influence or Control encompasses a wide variety of factual situations. An example of where Influence or Control exists would be where you, as a beneficiary of a revocable trust, have significant ongoing business and social relationships with the trustee of the trust. Examples of where Influence or Control does not exist would be a true blind trust, or securities held by a limited partnership in which your only participation is as a non-controlling limited partner. The determining factor in each case will be whether you (or any other Covered Person) have any direct or indirect Influence or Control over the securities account.

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Appendix B - Definitions

Terms used in this Code that are capitalized and bolded have a special meaning. To understand the Code, you need to understand the definitions of these terms below.

“Automatic Investment Plan” means a plan or other program in which regular periodic purchases or withdrawals are made automatically in or from investment accounts in accordance with a pre-determined schedule and allocation. These may include payroll deduction plans, issuer dividend reinvestment programs, 401(k) automatic investment plans, or the annual vesting of units into shares in a Mutual Fund Incentive Program.

“BAC” means Bank of America Corporation and its affiliates.

“BAC Retirement Plan” means any retirement plan sponsored by BAC for the benefit of its employees.

“Being Considered for Purchase or Sale” —  a security is being considered for purchase or sale when a recommendation to purchase or sell a security has been made and communicated or, with respect to the person making the recommendation, when such person decides to make the recommendation.

“Beneficial Ownership” has the meaning set forth in Appendix A, and refers to securities not only held by a Covered Person for his or her benefit, but also held by others for his or her benefit in an account over which the Covered Person has Influence or Control.

“CCO” means CWAM’s Chief Compliance Officer or his/her designee.

“Client” means any entity to which CWAM provides financial services.

“Client Account” means any investment management account or fund for which CWAM  acts as investment advisor or sub-advisor.

“Closed-end Fund” refers to a registered investment company whose shares are publicly traded in a secondary market rather than directly with the fund.

“Company-Directed 401(k) Plan” means a 401(k) plan that offers a limited number of investment options consisting solely of mutual funds in which one directs their investments. A 401(k) plan whereby the participant may direct stock investments is not a Company-Directed 401(k) Plan for purposes of this Code.

“Covered Person” is a person to whom this Code applies, including but not limited to CWAM officers, employees, and support partners.

“Family Holdings” and “Family/Household Member” refer to immediate family, sharing the same household as a Covered Person, or a family member outside of the household who is economically dependent on the Covered Person.

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“Federal Securities Laws” means the Securities Act of 1933 (15 U.S.C. 77a-aa), the Securities Exchange Act of 1934 (15 U.S.C. 78a –mm), the Sarbanes-Oxley Act of 2002 (Pub. L. 107-204, 116 Stat. 745 (2002)), the Investment Company Act of 1940 (15 U.S.C 80a), the Investment Advisers Act of 1940 (15 U.S.C. 80b), Title V of the Gramm-Leach-Bliley Act (Pub. L. No. 106-102, 113 Stat. 1338 (1999)), any rules adopted by the Commission under any of these statutes, the Bank Secrecy Act (31 U.S.C. 5311 –5314; 5316 – 5332) as it applies to funds and investment advisers, and any rules adopted thereunder by the Securities and Exchange Commission or the Department of Treasury.

“Influence or Control” has the meaning set forth in Appendix A, and refers to a person’s direct or indirect ability to affect the management of securities.

“Investment Account” means an account comprising all or a part of a person’s portfolio, held with a broker-dealer, bank, fund company, insurance company, or other entity capable of administering holdings of securities and funds on behalf of a client.

“Investment Person” refers to a Covered Person whose knowledge and influence on Client Accounts as a portfolio manager or research analyst necessitates the imposition of additional obligations and responsibilities under the Code.

“IPO” generally refers to a company’s first offer of shares to the public. Specifically, an offering of securities registered under the Securities Act of 1933, the issuer of which, immediately before the registration, was not subject to the reporting requirements of Sections 13 or 15(d) of the Securities Exchange Act of 1934.

“Late Trading” is the illegal trading of mutual funds wherein an order is placed after the fund is closed for the day and the transaction is priced using the closing price for that day.

“Limited Offering” generally refers to an offering of securities that is not offered to the public and includes an offering that is exempt from registration under the Securities Act of 1933 pursuant to Sections 4(2) or 4(6) of, or Regulation D under, the Securities Act of 1933.

“Market Timing” is the repeated buying, selling, or exchanging of fund shares by an individual or entity within short periods of time to take advantage of short-term differentials in the net asset values of such funds. This practice can occur in direct purchases and sales of fund shares, or through rapid reallocation of funds held in 401(k) plans or variable annuity or life policies.

“Reportable Fund” means shares of any open-end mutual fund registered under the Investment Company Act, other than money market funds or other short-term bond funds, whose investment adviser, sub-adviser or principal underwriter is controlled by Bank of America Corporation. The following companies are deemed to be controlled by Bank of America Corporation for purposes of this Code: Columbia Management Advisors, LLC, Columbia Management Distributors, Inc., Marsico Capital Management, LLC, Banc of America Capital Management (Ireland), Limited, Columbia Wanger Asset Management L.P., Grosvenor Capital Management, L.P. A list of Reportable Funds as of the date of the last revision of this Code is attached hereto as Appendix D.

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“Reportable Security” includes corporate securities, Closed-end Funds, and exchange traded funds. Reportable Securities therefore include anything that is considered a “security” under the Investment Advisers Act, but do not include:

1.	Any government obligations , including U.S., municipal, and foreign securities.
2.	Bankers’ acceptances, bank certificates of deposit, commercial paper and high quality short-term debt instruments, including repurchase agreements.
3.	Insurance company general accounts (short-term cash equivalent options of a variable life insurance policy).
4.	Shares of a money market fund or other short-term income or short-term bond funds.
5.	Shares of any open-end mutual fund, including any shares of a Reportable Fund.
6.	Futures and options on futures. However, a proposed trade in a “single stock future” (a security future which involves a contract for sale for future delivery of a single security) is subject to the Code’s pre-clearance requirement.

If you have any question or doubt about whether an investment is a Reportable Security under this Code, ask Compliance.

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Appendix C – Other CWAM and BAC Policies

·CWAM Statement of Operations and Supervisory Procedures Manual

·CWAM Information Wall Policy

·CWAM Misuses of Material Nonpublic Information Policy

·CWAM Portfolio Holdings Disclosure Policy

·Bank of America Corporation Code of Ethics and General Policy on Insider Trading

·Bank of America Global Wealth and Investment Management Associate Designated Brokerage Account Policy

·Bank of America Policy on Excessive Trading and Market Timing in the Bank of America Retirement Plans

·Bank of America Global Wealth and Investment Management Gifts and Hospitality Policy

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Appendix D – Reportable Funds

“Reportable Fund” means shares of any open-end mutual fund registered under the Investment Company Act, other than money market funds or other short-term bond funds, whose investment adviser, sub-adviser or principal underwriter is controlled by Bank of America Corporation. The following companies are deemed to be controlled by Bank of America Corporation for purposes of this Code: Columbia Management Advisors, LLC, Columbia Management Distributors, Inc., Marsico Capital Management, LLC, Banc of America Capital Management (Ireland), Limited, Columbia Wanger Asset Management L.P., Grosvenor Capital Management, L.P.

Columbia Management Advisors, LLC and Columbia Management Distributors, Inc.

CMG Core Bond Fund

CMG Enhanced S&P 500 Index Fund

CMG High Yield Fund

CMG International Stock Fund

CMG Large Cap Growth Fund

CMG Large Cap Value Fund

CMG Mid Cap Growth Fund

CMG Mid Cap Value Fund

CMG Small Cap Growth Fund

CMG Small Cap Value Fund

CMG Small/Mid Cap Fund

CMG Strategic Equity Fund

Columbia Acorn Fund

Columbia Acorn International

Columbia Acorn International Select

Columbia Acorn Select

Columbia Acorn USA

Columbia Asset Allocation Fund

Columbia Asset Allocation Fund II

Columbia Asset Allocation Fund, VS

Columbia Balanced Fund

Columbia California Intermediate Municipal Bond Fund

Columbia California Tax-Exempt Fund

Columbia Common Stock Fund

Columbia Connecticut Intermediate Municipal Bond Fund

Columbia Connecticut Tax-Exempt Fund

Columbia Conservative High Yield Fund

Columbia Convertible Securities Fund

Columbia Core Bond Fund

Columbia Disciplined Value Fund

Columbia Dividend Income Fund

Columbia Federal Securities Fund

Columbia Federal Securities Fund, VS

Columbia Florida Intermediate Municipal Bond Fund

Columbia Georgia Intermediate Municipal Bond Fund

Columbia Global Value Fund

Columbia Greater China Fund

Columbia Growth Stock Fund

Columbia High Income Fund

Columbia High Income Master Portfolio

Columbia High Yield Fund, VS

Columbia High Yield Municipal Fund

Columbia High Yield Opportunity Fund

Columbia Income Fund

Columbia Intermediate Bond Fund

Columbia Intermediate Core Bond Fund

Columbia Intermediate Core Bond Master Portfolio

Columbia Intermediate Municipal Bond Fund

Columbia International Fund, VS

Columbia International Stock Fund

Columbia International Value Fund

Columbia International Value Master Portfolio

Columbia Large Cap Core Fund

Columbia Large Cap Core Master Portfolio

Columbia Large Cap Enhanced Core Fund

Columbia Large Cap Growth Fund

Columbia Large Cap Growth Fund, VS

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Columbia Large Cap Index Fund

Columbia Large Cap Value Fund

Columbia Large Cap Value Fund, VS

Columbia Liberty Fund

Columbia LifeGoal Balanced Growth Portfolio

Columbia LifeGoal Growth Portfolio

Columbia LifeGoal Income & Growth Portfolio

Columbia LifeGoal Income Portfolio

Columbia Marsico 21st Century Fund

Columbia Marsico 21st Century Fund, VS

Columbia Marsico 21st Century Master Portfolio

Columbia Marsico Focused Equities Fund

Columbia Marsico Focused Equities Fund, VS

Columbia Marsico Focused Equities Master Portfolio

Columbia Marsico Growth Fund

Columbia Marsico Growth Fund, VS

Columbia Marsico Growth Master Portfolio

Columbia Marsico International Opportunities Fund

Columbia Marsico International Opportunities Fund, VS

Columbia Marsico International Opportunities Master Portfolio

Columbia Marsico Mid Cap Growth Fund

Columbia Marsico Mid Cap Growth Fund, VS

Columbia Maryland Intermediate Municipal Bond Fund

Columbia Massachusetts Intermediate Municipal Bond Fund

Columbia Massachusetts Tax-Exempt Fund

Columbia Masters Global Equity Portfolio

Columbia Masters Heritage Portfolio

Columbia Masters International Equity Portfolio

Columbia Mid Cap Growth Fund

Columbia Mid Cap Index Fund

Columbia Mid Cap Value Fund

Columbia Mid Cap Value Fund, VS

Columbia Multi-Advisor International Equity Fund

Columbia Multi-Advisor International Equity Master Portfolio

Columbia Municipal Income Fund

Columbia New Jersey Intermediate Municipal Bond Fund

Columbia New York Intermediate Municipal Bond Fund

Columbia New York Tax-Exempt Fund

Columbia North Carolina Intermediate Municipal Bond Fund

Columbia Oregon Intermediate Municipal Bond Fund

Columbia Real Estate Equity Fund

Columbia Rhode Island Intermediate Municipal Bond

Columbia S&P 500 Index Fund, VS

Columbia Small Cap Core Fund

Columbia Small Cap Growth Fund I

Columbia Small Cap Growth Fund II

Columbia Small Cap Growth Master Portfolio II

Columbia Small Cap Index Fund

Columbia Small Cap Value Fund I

Columbia Small Cap Value Fund II

Columbia Small Cap Value Fund, VS

Columbia Small Cap Value II Master Portfolio

Columbia Small Company Equity Fund

Columbia Small Company Growth Fund, VS

Columbia South Carolina Intermediate Municipal Bond Fund

Columbia Strategic Income Fund

Columbia Strategic Income Fund, VS

Columbia Strategic Investor Fund

Columbia Tax-Exempt Fund

Columbia Tax-Exempt Insured Fund

Columbia Tax-Managed Growth Fund

Columbia Technology Fund

Columbia Texas Intermediate Municipal Bond Fund

Columbia Thermostat Fund

Columbia Total Return Bond Fund

Columbia U.S. Treasury Index Fund

Columbia Utilities Fund

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Columbia Virginia Intermediate Municipal Bond Fund

Columbia World Equity Fund

Columbia Young Investor Fund

Corporate Bond Portfolio

Mortgage and Asset Backed Portfolio

Wanger International Select

Wanger International Small Cap

Wanger Select

Wanger US Smaller Companies

CMA Sub-Advised Funds

ALZ Columbia Technology Portfolio

ING Columbia Small Cap Value II Portfolio

Merrill Lynch Global Selects High Yield

Merrill Lynch Global Selects Small Cap

Nordea High Yield Bond Fund

Pacific Life: Pacific Select Fund, Technology Portfolio

Columbia Wanger Asset Management, L.P.

Columbia Funds

Columbia Acorn Fund

Columbia Acorn USA

Columbia Acorn Select

Columbia Acorn International

Columbia Acorn International Select

Columbia Thermostat

Wanger Funds

Wanger US Smaller Companies

Wanger Select

Wanger International Small Cap

Wanger International Select

Wanger US Smaller Companies

Wanger European Smaller Companies

Optimum Funds

Optimum Small Cap Growth

RiverSource Funds

RiverSource International Aggressive Growth

Marsico Capital Management, LLC

Columbia Funds

Columbia Marsico Focused Equities Master Portfolio

Columbia Marsico Growth Master Portfolio

Columbia Marsico 21st Century Master Portfolio

Columbia Marsico Mid Cap Growth Fund

Columbia Marsico International Opportunities Fund

Columbia Multi-Advisor International Equity Fund

Columbia Marsico Focused Equities Fund, Variable Series

Columbia Marsico Growth Fund, Variable Series

Columbia Marsico 21st Century Fund, Variable Series

Columbia Marsico Mid Cap Growth Fund, Variable Series

Columbia Marsico In’tl Opportunities Fund, Variable Series

(The) Marsico Investment Fund

Marsico Focus Fund

Marsico Growth Fund

Marsico 21st Century Fund

Marsico International Opportunities Fund

AEGON/Transamerica Series Fund, Inc.

TA/IDEX Marsico Growth Fund

ATST Marsico Growth Fund

TA/IDEX Marsico International Growth Fund

American Skandia Trust/Prudential Investments

Strategic Partners Capital Growth

AST Marsico Capital Growth

AST Advanced Strategies Portfolio

Target Portfolio Trust – Large Cap Growth

Strategic Partners Conservative Allocation Fund

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Strategic Partners Moderate Allocation Fund

Strategic Partners Growth Allocation Fund

Prudential Series Fund Global Portfolio

AXA Funds

AXA Enterprise Multimanager International Equity Fund

AXA Premier VIP International Equity Fund

AXA Premier VIP Aggressive Equity Portfolio

EQ/Marsico Focus Portfolio

AXA/Enterprise Capital Appreciation Fund

Counsel Group of Funds

Counsel Select America

Discovery Group of Funds (Luxembourg SICAV)

Global

North America

North America Large Cap Ethical GES

(The) Diversified Investors Funds Group

Diversified Investors Equity Growth Fund

Frank Russell Investment Company

Equity I Fund

Diversified Equity Fund

Frank Russell Multi Style, Multi-Manager Funds PLC

The U.S. Equity Fund (UCITS)

Frank Russell Investment Company PLC II (Irish)

U.S. Growth Equity Fund (UCITS)

GuideStone Funds

Growth Equity Fund

Harbor Fund

Harbor International Growth Fund

ING Investors Trust

ING Marsico Growth Portfolio

ING Marsico International Opportunities Portfolio

Jefferson Pilot Variable Fund, Inc.

International Equity Portfolio

John Hancock Trust

International Opportunities Trust

John Hancock Funds II

Funds II International Opportunities Trust

Masters Select Funds Trust

Masters Select International Fund

Merrill Lynch

Global Selects Portfolios PLC - North American Large Cap Growth Portfolio III

Marsico Growth FDP Fund of FDP Series, Inc.

Roszel/Marsico Large Cap Growth Portfolio

Optimum Fund Trust

Optimum Large Cap Growth Fund

RiverSource

RiverSource International Equity Fund

Skandia Global Funds PLC

Skandia-Marsico US Capital Growth Fund (UCITS)

SunAmerica Asset Management

Focused Series Large Cap Growth Portfolio

Focused Series Growth and Income Portfolio

Focused Series International Equity Portfolio

Season Series Trust Focus Growth Portfolio

Season Series Trust Focus Growth & Income Portfolio

SunAmerica Series Trust Marsico Growth Portfolio

SunAmerica Focused Alpha Growth Fund

SunAmerica Focused Alpha Large-Cap Fund

UBS Pace Select Advisors Trust

Large Company Growth Equity Investments Fund

USAA

USAA Growth Fund

USAA Aggressive Growth Fund

USAA Life Aggressive Growth Fund

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Appendix E – Reporting Forms

INITIAL HOLDINGS REPORT
For New CWAM Covered and Investment Persons 

Please complete this form and submit it to the Compliance Department (37th floor) no later than 10 days after you become a Covered Person of Columbia Wanger Asset Management.

YOU MUST REPORT: all investment accounts, holding or capable of holding Reportable Securities or Reportable Funds, in which you have “Beneficial Ownership,” and investment discretion, influence or control. “Beneficial Ownership” includes shares held in your name and/or the name of (1) your spouse, (2) your minor children, (3) your adult children and relatives who live in your home, (4) any nominee or other person if you can reacquire title now or in the future. (See Page 20 for further clarification)

YOU NEED NOT REPORT: BAC Retirement Plans, Company-Directed 401(k) Plans (that cannot hold Reportable Funds or Reportable Securities), 529 Plans, accounts in which you have “Beneficial Ownership” but not investment discretion, influence or control, US Government Securities, commercial paper, certificates of deposit, repurchase agreements, banker’s acceptance, and any other money market instruments, municipal bonds, index options, and mutual funds not advised or controlled by Bank of America Corporation.

Name:

1.  Code Classification

I understand that for purposes of the Code I am classified as:

o Covered Person

o An Investment Person

2.  Personal Holdings

o Neither I, nor any member of my Family/Household, have Beneficial Ownership of Investment Accounts or Personal Holdings of any Reportable Securities or Reportable Funds.

o I and/or a member of my Family/Household have Beneficial Ownership of an Investment Account, but this Investment Account is not subject to my (or my Family/Household member’s) control and discretion.

o I and/or a member of my Family/Household have Beneficial Ownership of Investment Accounts or Personal Holdings of Reportable Securities and/or Reportable Funds, and these holdings are subject to my (or my Family/Household member’s) control and discretion.*

3.  Initial Certification

o I have read the Code, and will keep a copy for future reference. I understand my responsibilities under the Code and agree to comply with all of its terms and conditions. In particular, I understand that the Code applies to me and to all investments in which I have Beneficial Ownership, as well as investments in which members of my Family/Household have Beneficial Ownership.

All information provided in this Form A is true and complete to the best of my knowledge.

Signature:   Date:

*  Please provide photocopies of the most recent statements from your reported accounts and holdings.

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QUARTERLY PERSONAL SECURITIES TRANSACTIONS
REPORT FOR CWAM COVERED AND INVESTMENT PERSONS 

Please complete this form and submit it to the Compliance Department (37th floor) no later than 30 days after each quarter-end (March, June, September, December).

YOU MUST REPORT: all transactions (whether voluntary or automatic) in Reportable Securities and Reportable Funds of which you have “Beneficial Ownership.” “Beneficial Ownership” includes shares held in the name of (1) your spouse, (2) your minor children, (3) your adult children and relatives who live in your home, (4) any nominee or other person if you can reacquire title now or in the future.

YOU NEED NOT REPORT: Transactions in accounts, funds and securities that are not subject to initial reporting requirements such as: US Government Securities, commercial paper, certificates of deposit, repurchase agreements, banker’s acceptance, and any other money market instruments, municipal bonds, index options, and mutual funds not advised or controlled by Bank of America Corporation.

Name:

Status:  o Covered    o InvestmentFor Quarter:  o 1    o 2    o 3    o 4

1.  Transactions  (Please check one.)

oI have made no reportable transactions during this quarter.

oI have made reportable transactions during this quarter.*

2.  Statements  (Please check all that apply.)

oI have no reportable accounts and, as such, no statements to submit.

oDuplicate statements are sent directly to Compliance from the broker or dealer.

oI have provided photocopies of account statements.

3.  New Accounts (Please check one.)

oI have not opened a new account during the quarter.

oI have opened a new account(s) during the quarter.**

Signature:   Date:

*	Such transactions should appear in statements submitted to Compliance. Please use the reverse side of this form to describe any transactions that do not appear on submitted statements
**	Please submit the following information to Compliance: Name on Account, Institution Name, Account Number, and Date Account was Opened.

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ANNUAL RECERTIFICATION Code of Ethics, Policy Concerning Material Non-PublicInformation, & Personal Holdings 

Please complete Sections 1-3 of this form and submit it to the Compliance Department (37th floor) no later than 30 days after the year-end.

Name:                                                                                                       Status:  o Covered    o Investment

1.    Code of Ethics

(Please initial both affirmations.)

A.I have read the Code, and will keep a copy for future reference. I understand my responsibilities under the Code and agree to comply with all of its terms and conditions. In particular, I understand that the Code applies to me and to all investments in which I have Beneficial Ownership, as well as investments in which members of my Family/Household have Beneficial Ownership.

Initials: 

B.I hereby certify that during the year covered by this report December 31,            , I complied with all applicable requirements of the Code and have reported to Compliance all transactions required to be reported under the Code. *

Initials: 

* Please describe Code violations or instances of non-compliance on a separate attachment.

2.    Additional CWAM Policies

(Please initial the following three affirmations.)

A.I have read the CWAM Statement of Operations and Supervisory Procedures Manual  (and its Appendices, including: Policy & Procedures Concerning Material Non-Public Information, and the Information Wall Policy), and the CWAM Portfolio Holdings Disclosure Policy and understand my responsibilities under these policies and acknowledge compliance with these policies.

Initials: 

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3.    Personal Holdings & Exemptions

(Please check all that apply.)

o Neither I, nor any member of my Family/Household, have Beneficial Ownership of Investment Accounts or Personal Holdings of any Reportable Securities or Reportable Funds.

o I and/or a member of my Family/Household have Beneficial Ownership of an Investment Account, but this Investment Account is not subject to my (or my Family/Household member’s) control and discretion.

o I and/or a member of my Family/Household have Beneficial Ownership of Investment Accounts or Personal Holdings of Reportable Securities and/or Reportable Funds, and these holdings are subject to my (or my Family/Household member’s) control and discretion. (Please list all such accounts/holdings on a separate attachment.)

All information provided in this Form C is true and complete to the best of my knowledge.

Signature:   Date:

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COLUMBIA WANGER ASSET MANAGEMENT
MULTI-APPROVAL FORM 

ATTENTION:  To ensure efficient processing, submit the completed form via email to: Joe LaPalm or Bruce Lauer.

SECTION I:  REQUIRED – Complete or check ALL of these required fields.
Name		Date
SECTION II:  IPO, Hedge Fund or Private Placement Transaction Request for Approval
Security name / description:	Broker-Dealer handling the transaction:
Your relationship to the offering:	Is the security eligible for accounts in which you are associated?  If not, where will the security be held?
How did you hear about it?	Other relevant information & attach documentation:
What is the principal amount of your requested transaction?
SECTION III:  Bank of America Affiliate Advised Closed-end Fund Transaction Request for Approval
Security name / description:	Broker-Dealer handling the transaction:
What is your relationship to the offering?	Is the security eligible for accounts in which you are associated?  If not, where will the security be held?
What is the principal amount of your requested transaction?	Other relevant information & attach documentation:
Section IV:  Officer/Director of Public Company Request for Approval
Are you an Investment Person?     YES  or  NO Firm Name:	Position being requested:
Expected time period for position being held:	Explain how the position would not be a conflict and other relevant information & attach documentation:

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Compliance Decision

Permission to Grant Approval to the Code Requirement:
	YES	NO	Effective date:	Manager Approval
Compliance Approval:

For Compliance Purposes Only:
Date Compliance Received:	Compliance Officer Handling:
Date Compliance Responded:
Date Associate Notified:	Method of Reporting to Associate:

Multi-Approval Form

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EX-99.P.2

Exhibit 99.p.2

COLUMBIA ACORN TRUST
WANGER ADVISORS TRUST

Code of Ethics
for
Non-Management Trustees

The Investment Company Act of 1940, as amended (the “1940 Act”) and rules thereunder require that Columbia Acorn Trust and Wanger Advisors Trust (the “Trusts”) establish standards and procedures for the detection and prevention of certain conflicts of interest, including activities by which persons having knowledge of the investments and investment intentions of the series of each Trust (each a “Fund” and collectively, the “Funds”) might take advantage of that knowledge for their own benefit.  For that purpose, each Trust has adopted this Code of Ethics (the “Code”) applicable to those members of the Trust’s board of trustees who are not affiliated with Columbia Wanger Asset Management, L.P. (“CWAM”), the investment adviser of the Trusts.

Any questions about the Code or about the applicability of the Code to a personal securities transaction should be directed to CWAM’s designated compliance officer, the Trusts’ chief compliance officer or counsel for the Trusts.

I.  STATEMENT OF PRINCIPLE

General Prohibitions.  The 1940 Act and rules thereunder make it illegal for any person covered by the Code, directly or indirectly, in connection with the purchase or sale of a security held or to be acquired by a Fund to:

a.employ any device, scheme, or artifice to defraud the Fund;

b.make to the Fund any untrue statement of a material fact or omit to state to the Fund a material fact necessary in order to make the statements made, in light of cir­cumstances under which they are made, not misleading;

c.engage in any act, practice, or course of business which operates or would operate as a fraud or deceit upon the Fund; or

d.engage in any manipulative practice with respect to the Fund.

Personal Securities Transactions.  The Code regulates personal securities transactions as a part of the effort by the Funds to detect and prevent conduct that might violate the general prohibitions outlined above.  A personal securities transaction is a transaction in a Covered Security held in any account over which the Non-Management Trustee, as defined below, has a beneficial interest, also as defined below.

Covered Security is interpreted very broadly for this purpose, and includes any right to acquire any security (an option or warrant, for example).

You have a beneficial interest in a security in which you have, directly or indirectly, the opportunity to profit or share in any profit derived from a transaction in the security, or in which you have an indirect interest, including beneficial ownership by your spouse or minor children or other dependents living in your household, or your share of securities held by a partnership of which you are a general partner.  Technically, the rules under section 16 of the Securities Exchange Act of 1934 will be applied to determine if you have a beneficial interest in a security (even if the security would not be within the scope of section 16).  Examples of beneficial interest and a copy of Rule 16a-1(a), defining beneficial ownership, are attached as Appendix B.

In any situation where the potential for conflict exists, transactions for a Fund must take precedence over any personal transaction.  Each Fund’s Non-Management Trustees owe a duty to the Fund and its shareholders to conduct their personal securities transactions in a manner which does not interfere with the portfolio transactions of the Fund, take inappropriate advantage of their relationship with the Fund, or create any actual or potential conflict of interest between their interests and the interests of the Fund and its shareholders.

Situations not specifically governed by this Code of Ethics will be resolved in light of this general principle.

II.  TO WHOM THE CODE’S RESTRICTIONS APPLY

The Code applies to each board member who is not an “interested person” of the Funds within the meaning of Section 2(a)(19) of the 1940 Act, including any board member who is not an “interested person” of the Funds within the meaning of Section 2(a)(19) of the 1940 Act but whom the boards have determined to treat as an “interested person” of the Funds (the “Non-Management Trustees”).  The Non-Management Trustees are listed on Appendix A hereto.

III.  RESTRICTIONS ON PERSONAL SECURITIES TRANSACTIONS

A.No Transactions with the Funds.  No Non-Management Trustee shall knowingly sell to, or purchase from the Funds any security or other property, except securities issued by the Funds.

B.No Conflicting Transactions.  No Non-Management Trustee shall purchase or sell any security in which such Non-Management Trustee has or would thereby acquire a beneficial interest which the person knows or has reason to believe is being purchased or sold or considered for purchase or sale by the Funds, until the Funds’ transactions have been completed or consideration of such transactions has been abandoned.

IV.  COMPLIANCE PROCEDURES

A.Quarterly Reporting of Personal Securities Transactions.

1.Each Non-Management Trustee shall report to CWAM’s compliance officer, within ten days after the end of the calendar quarter in which a reportable transaction occurs, any personal securities transaction in which the Non-Management Trustee, at the time of the transaction, knew, or in the ordinary

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course of fulfilling his or her duties as a trustee should have known, that on the day of the transaction or within 15 days before or after that day a purchase or sale of that security was made by or considered for the Funds.

2.Quarterly reports of personal securities transactions for Non-Management Trustees may be in any form (including copies of confirmations or monthly statements) but must include (i) the date of the transaction, the title and number of shares, and the principal amount of each security involved; (ii) the nature of the transaction (i.e., purchase, sale, gift, or other type of acquisition or disposition); (iii) the price at which the transaction was effected; (iv) the name of the broker, dealer, or bank with or through whom the transaction was effected; and (v) the name of the reporting person.

B. Monitoring of Transactions.  CWAM’s compliance officer will review the quarterly reports of personal securities transactions of each Fund’s Non-Management Trustees.

D.Certification of Compliance.  Each Non-Management Trustee is required to certify annually that he or she has read and understands the Code and recognizes that he or she is subject to the Code.  To accomplish this, the Secretary of the Funds shall annually distribute a copy of the Code and request certification.

E.Review by the Funds’ Boards.  The officers of the Funds shall prepare an annual report to the boards that:

1.summarizes existing procedures concerning personal investing and any changes in those procedures during the past year;

2.identifies any violations of the Code requiring significant remedial action during the past year; and

3.identifies any recommended changes in existing restrictions or proce­dures based upon experience under the Code, evolving industry practices, or developments in applicable laws or regulations.

V.            EXEMPT TRANSACTIONS

The provisions of this Code are intended to restrict the personal investment activities of persons subject to the Code only to the extent necessary to accomplish the purposes of the Code.  Therefore, the provisions of Section III (Restrictions on Personal Securities Transactions) and Section IV (Compliance Procedures) of this Code shall not apply to:

A.Purchases or sales effected in any account over which the persons subject to this Code have no direct or indirect influence or control;

B.Purchases or sales of:

1.U.S. government securities;

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2.shares of open-end investment companies (mutual funds), including but not limited to shares of any of the Funds; and

3.bank certificates of deposit or commercial paper.

C.Purchases or sales over which neither the person subject to this Code nor the Funds have control;

D.Purchases that are part of an automatic dividend reinvestment plan;

E.Purchases effected upon the exercise of rights issued by an issuer pro rata to all holders of a class of securities to the extent such rights were acquired from such issuer, and sales of such rights so acquired;

F.Purchases or sales in an account managed by an independent investment adviser with discretion where the Non-Management Trustee has no advance knowledge of the transactions before they had been executed; and

G.Purchases or sales that receive the prior approval of the Funds’ compliance officer because they are not inconsistent with this Code or the provisions of Rule 17j-1(a) under the 1940 Act.

VI.  CONSEQUENCES OF FAILURE TO COMPLY WITH THE CODE

Compliance with this Code is a condition of retention of positions with the Funds.  The Funds’ boards of trustees shall determine what action is appropriate for any breach of the provisions of the Code by a Non-Management Trustee, which may include removal from the boards.

Reports filed pursuant to the Code will be maintained in confidence but will be reviewed by CWAM or the Funds to verify compliance with the Code.  Additional information may be required to clarify the nature of particular transactions.

VII.  RETENTION OF RECORDS

CWAM’s designated compliance officer shall maintain the records listed below for a period of five years at the Funds’ principal place of business in an easily accessible place:

A.a list of all persons subject to the Code during the period;

B.receipts signed by all persons subject to the Code acknowledging receipt of copies of the Code and acknowledging that they are subject to it;

C.a copy of each code of ethics that has been in effect at any time during the period; and

D.a copy of each report filed pursuant to the Code and a record of any known violation and action taken as a result thereof during the period.

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*                              *                              *                              *                              *

Columbia Acorn Trust:

Adopted effective 5/28/96
Amended effective 5/25/99
Amended effective 9/29/00
Amended effective 5/23/01
Amended effective 3/4/02
Amended effective 11/16/04
Amended effective 6/6/06
Amended effective 9/26//06

Wanger Advisors Trust:

Adopted effective 6/15/96
Amended effective 6/8/99
Amended effective 9/29/00
Amended effective 6/5/01
Amended effective 12/28/03
Amended effective 6/7/06
 Amended effective 9/26//06

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Appendix A

Non-Management Trustees
Margaret Eisen
Jerome Kahn, Jr.
Steven Kaplan
David C. Kleinman
Allan B. Muchin
Robert E. Nason
James A. Star
Ralph Wanger
Patricia H. Werhane
John A. Wing

Appendix B

Examples of Beneficial Ownership

For purposes of the Code, you will be deemed to have a beneficial interest in a security if you have the opportunity, directly or indirectly, to profit or share in any profit derived from a transaction in the security.  Examples of beneficial ownership under this definition include:

·securities you own, no matter how they are registered, and including securities held for you by others (for example, by a custodian or broker, or by a relative, executor or administrator) or that you have pledged to another (as security for a loan, for example);

·securities held by a trust of which you are a beneficiary (except that, if your interest is a remainder interest and you do not have or participate in investment control of trust assets, you will not be deemed to have a beneficial interest in securities held by the trust);

·securities held by you as trustee or co-trustee, where either you or any member of your immediate family (i.e., spouse, children or descendants, stepchildren, parents and their ancestors, and stepparents, in each case treating a legal adoption as blood relationship) has a beneficial interest (using these rules) in the trust;

·securities held by a trust of which you are the settlor, if you have the power to revoke the trust without obtaining the consent of all the beneficiaries and have or participate in investment control;

·securities held by any partnership in which you are a general partner, to the extent of your interest in partnership capital or profits;

·securities held by a personal holding company controlled by you alone or jointly with others;

·securities held by (i) your spouse, unless legally separated, or you and your spouse jointly, or (ii) your minor children or any immediate family member of you or your spouse (including an adult relative), directly or through a trust, who is sharing your home, even if the securities were not received from you and the income from the securities is not actually used for the maintenance of your household; or

·securities you have the right to acquire (for example, through the exercise of a derivative security), even if the right is not presently exercisable, or securities as to which, through any other type of arrangement, you obtain benefits substantially equivalent to those of ownership.

You will not be deemed to have beneficial ownership of securities in the following situations:

·securities held by a limited partnership in which you do not have a controlling interest and do not have or share investment control over the partnership’s portfolio; and

·securities held by a foundation of which you are a trustee and donor, provided that the beneficiaries are exclusively charitable and you have no right to revoke the gift.

These examples are not exclusive.  There are other circumstances in which you may be deemed to have a beneficial interest in a security.  Any questions about whether you have a beneficial interest should be directed to CWAM’s designated compliance officer or chief operating officer.

Attachment A

COLUMBIA ACORN TRUST
WANGER ADVISORS TRUST

Code of Ethics Affirmation

I affirm that I have received a copy of the Columbia Acorn Trust and Wanger Advisors Trust Code of Ethics for Non-Management Trustees (the “Code”) and have read and understand it.  I acknowledge that I am subject to the Code and will comply with the Code in all respects.

Date:
	Signature