COLUMBIA ACORN TRUST

Columbia^SM Acorn International Select^®

Columbia^SM Acorn International^®

Columbia^SM Acorn Select^®

Columbia^SM Acorn USA^®

Columbia^SM Acorn^® Fund

Columbia^SM Thermostat Fund^®

(the “Funds”)

Supplement dated September 3, 2010

to the Statement of Additional Information (“SAI”) dated May 1, 2010

Effective September 7, 2010 (the Effective Date), the Funds will share the same policies and procedures for investor services as the other Columbia funds and the RiverSource funds (including the Seligman and Threadneedle branded funds), as described below in this Supplement and in the prospectuses, as supplemented.

As of the Effective Date, the Funds’ SAI dated May 1, 2010 is supplemented as follows:

(1) The second paragraph of the section entitled Brokerage Allocation and Other Practices – Additional Financial Intermediary Payments – Marketing Support Payments is replaced with the following:

While the financial arrangements may vary for each financial intermediary, the marketing support payments to each financial intermediary generally are expected to be between 0.05% and 0.50% on an annual basis for payments based on average net assets of the Funds attributable to the financial intermediary, and between 0.05% and 0.25% on an annual basis for firms receiving a payment based on gross sales of the Columbia Funds attributable to the financial intermediary. The Distributor and affiliates may make payments in larger amounts or on a basis other than those described above when dealing with certain selling and/or servicing agents, including certain affiliates of Bank of America Corporation (Bank of America). Such increased payments may enable such selling and/or servicing agents to offset credits that they may provide to their customers.

(2) The text of the section entitled Purchase, Redemption and Pricing of Shares – Purchase and Redemption –Front-End Sales Charge Waivers is replaced with the following:

The following investors buy Class A shares without paying a front-end sales charge:

• Employees of Bank of America, its affiliates and subsidiaries.

• Employees or partners of Marsico Capital Management, LLC (or its successors).

• 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.

• 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 buy Class A shares of any Fund without paying a front-end sales charge in those cases where a Columbia Fund Class Z share is not available.

• Galaxy Fund shareholders prior to December 1, 1995; and shareholders who (i) bought Galaxy Fund Prime A shares without paying a front-end sales charge 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 bought.

• Current or retired Fund Board members, officers or employees of the Funds or the Advisor or its affiliates (and their spouses or domestic partners, children or step-children, parents, step-parents or legal guardians, and their spouse’s or domestic partner’s parents, step-parents, or legal guardians).

• Current or retired Ameriprise Financial Services, Inc. financial advisors and employees of such financial advisors (and their spouses or domestic partners, children or step-children, parents, step-parents or legal guardians, and their spouse’s or domestic partner’s parents, step-parents, or legal guardians).

• Registered representatives and other employees of affiliated or unaffiliated selling and/or servicing agent having a selling agreement with the Distributor (and their spouses or domestic

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partners, children or step-children, parents, step-parents or legal guardians, and their spouse’s or domestic partner’s parents, step-parents, or legal guardians).

• Registered broker/dealer firms that have entered into a dealer agreement with the Distributor may buy Class A shares without paying a front-end sales charge for their investment account only.

• Portfolio managers employed by subadvisers of the Columbia or RiverSource funds (and their spouses or domestic partners, children or step-children, parents, step-parents or legal guardians, and their spouse’s or domestic partner’s parents, step-parents, or legal guardians).

• Partners and employees of outside legal counsel to the Funds or the Funds’ directors or trustees who regularly provide advice and services to the Funds, or to their directors or trustees.

• Direct rollovers from qualified employee benefit plans, provided that the rollover involves a transfer to Class A shares in the same Fund.

• Purchases made:

• With dividend or capital gain distributions from a Fund or from the same class of another Fund;

• Through or under a wrap fee product or other investment product sponsored by a selling and/or servicing agent that charges an account management fee or other managed agency/asset allocation accounts or programs involving fee-based compensation arrangements that have or that clear trades through a selling and/or servicing agent that has a selling agreement with the Distributor;

• Through state sponsored college savings plans established under Section 529 of the Internal Revenue Code; or

• Through banks, trust companies and thrift institutions, acting as fiduciaries.

• Separate accounts established and maintained by an insurance company which are exempt from registration under Section 3(c)(11).

• Purchases made through “employee benefit plans” created under section 401(a), 401(k), 457 and 403(b), and qualified deferred compensation plans, that have a plan level or omnibus account maintained with the Fund or the Transfer Agent and transacts directly with the Fund or the Transfer Agent through a third party administrator or third party recordkeeper.

• At the Fund’s discretion, front-end sales charges 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.

Investors can also buy Class A shares without paying a sales charge if the purchase is made from the proceeds of a sale from any Columbia Fund Class A, B, C or T shares within 90 days, up to the amount of the sales proceeds. In addition, shareholders of the money market fund series of BofA Funds Series Trust, which were formerly referred to as the Columbia Money Market Funds (the Former Columbia Money Market Funds), can also buy Class A shares of the Columbia Funds without paying a sales charge if the purchase is made from the proceeds of a sale of shares from a Former Columbia Money Market Fund within 90 days, up to the amount of the sales proceeds, provided that the proceeds are from the sale of shares of a Former Columbia Money Market Fund purchased on or before April 30, 2010. To be eligible for these reinstatement privileges the purchase must be made into an account for the same owner, but does not need to be into the same Columbia Fund from which the shares were sold. The Transfer Agent, Distributor or their agents must receive a written reinstatement request within 90 days after the shares are sold and the purchase of Class A shares through this reinstatement privilege will be made at the NAV of such shares next calculated after the request is received in good order.

Restrictions may apply to certain accounts and certain transactions. The Fund may change or cancel these terms at any time. Any change or cancellation applies only to future purchases. Unless you provide your financial advisor with information in writing about all of the factors that may count toward a waiver of the sales charge, there can be no assurance that you will receive all of the waivers for which you may be eligible. You should request that your financial advisor provide this information to the Fund when placing your purchase

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order. For more information about the sales charge reductions and waivers described here, as well as additional categories of eligible investors, please see the prospectuses.

(3) The text of the section entitled Purchase, Redemption and Pricing of Shares – Purchase and Redemption – Contingent Deferred Sales Charge Waivers is replaced with the following:

Shareholders won’t pay a CDSC in the following circumstances:

Death: CDSCs may be waived on sales made in the event of the shareholder’s death.

Disability: CDSCs may be waived on sales after the sole shareholder on an individual account or a joint tenant on a joint tenant account becomes disabled (as defined by Section 72(m)(7) of the Code). To be eligible for such a waiver: (i) the disability must arise after the account is opened and (ii) 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 shares are sold, the applicable CDSC will be charged.*

Health savings accounts: For shares purchased prior to September 7, 2010, CDSCs may be waived on shares sold by health savings accounts sponsored by third party platforms, including those sponsored by Bank of America affiliates.*

Medical payments: For shares purchased prior to September 7, 2010, CDSCs may be waived on shares sold for medical payments that exceed 7.5% of income.*

Certain purchases of medical insurance: CDSCs may be waived on distributions from sales made to pay for medical 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.*

Systematic Withdrawal Plan (SWP): For shares purchased prior to September 7, 2010, CDSCs may be waived on sales occurring pursuant to a SWP established with the Transfer Agent, to the extent that the sales do not exceed, on an annual basis, 12% of the account’s value as long as distributions are reinvested. Otherwise, a CDSC will be charged on SWP sales until this requirement is met.

Qualified retirement plans: CDSCs may be waived on shares (except for Class B shares) sold by certain group retirement plans held in omnibus accounts. CDSCs may be waived on redemptions of Class A shares initially purchased by an employee benefit plan. However, CDSC may not be waived for Class C shares if the waiver would occur as a result of a plan-level termination.

Redemptions under certain retirement plans and accounts: CDSCs may be waived on shares sold (i) prior to September 7, 2010 in connection with distributions from qualified retirement plans, government (Section 457) plans, individual retirement accounts or custodial accounts under Section 403(b)(7) of the Code following normal retirement or the attainment of age 59^1/2, and following normal retirement age or the attainment of age 70^1/2, and (ii) on or after September 7, 2010 as a result of required minimum distributions taken from retirement accounts upon the shareholder’s attainment of age 70^1/2.**

Loans from qualified retirement plans: For Class B shares, and for Class A and Class C shares purchased prior to September 7, 2010, CDSCs may be waived on shares sold in connection with loans from qualified retirement plans to shareholders.*

Accounts liquidated by the Fund: CDSCs may be waived for shares sold in an account that has been closed because it falls below the minimum account balance.

Returns of excess contributions: CDSCs may be waived on sales of shares (except for Class B shares) that result from returns of excess contributions made to retirement plans or individual retirement accounts, so

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long as the selling and/or servicing agent returns the applicable portion of any commission paid by the Distributor.

Return of commission: CDSCs may be waived on shares (except for Class B shares) for which no sales commission or transaction fee was paid to an authorized selling and/or servicing agent at the time of purchase.

Plans of reorganization: At a Fund’s discretion, CDSCs may be waived for shares (except for Class B shares) issued in connection with plans of reorganization, including but not limited to mergers, asset acquisitions and exchange offers, to which the Fund is a party.

* Shareholders and selling and/or servicing agents must inform the Fund or the Transfer Agent in writing that the shareholders qualifies for the particular sales charge waiver and provide proof thereof.

** For direct trades on non-prototype retirement accounts where the date of birth of the shareholder is not maintained, the shareholder or selling and/or servicing agent must inform the Fund or the Transfer Agent in writing that the shareholders qualifies for the particular sales charge waiver and provide proof thereof.

Restrictions may apply to certain accounts and certain transactions. The Fund may change or cancel these terms at any time. Any change or cancellation applies only to future purchases. For more information about the sales charge reductions and waivers described here, as well as additional categories of eligible redemptions, see the Funds’ prospectuses.

(4) The following is added as a new section before the section entitled Purchase, Redemption and Pricing of Shares – Purchase and Redemption – Anti-Money Laundering Compliance:

Minimum Initial Investment in Class Z Shares

Class Z shares are available only to certain eligible investors, which are subject to different minimum initial investment requirements described in the prospectus, as supplemented. In addition to the categories of Class Z investors described in the prospectus, as supplemented, the minimum initial investments in Class Z shares are as follows:

• There is no minimum initial investment in Class Z shares for any health savings account sponsored by a third party platform, including those sponsored by affiliates of Bank of America.

• The minimum initial investment in Class Z shares for the following categories of eligible investors is $2,000:

• Any client of Bank of America or one of its subsidiaries buying shares through an asset management company, trust, fiduciary, retirement plan administration or similar arrangement with Bank of America or the subsidiary.

• Any employee (or family member of an employee) of Bank of America or one of its subsidiaries.

Shareholders should retain this Supplement for future reference.

C-6516-1 A (8/10)

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