| Fund | Prospectus and Summary Prospectus Dated |
| Columbia Acorn Trust | |
| Columbia Acorn® Fund | 5/1/2016 |
| 1. | The table under the caption “Fees and Expenses of the Fund” in the “Summary of the Fund” section of the Prospectus and the Summary Prospectus is hereby superseded and replaced with the following: |
| Shareholder Fees (fees paid directly from your investment) | |||
| Class A | Class C | Classes
I, R4, R5, Y and Z | |
| Maximum sales charge (load) imposed on purchases (as a % of offering price) | 5.75% | None | None |
| Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value) | 1.00% (a) | 1.00% (b) | None |
| Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment) | |||||||
| Class A | Class C | Class I | Class R4 | Class R5 | Class Y | Class Z | |
| Management fees | 0.65% | 0.65% | 0.65% | 0.65% | 0.65% | 0.65% | 0.65% |
| Distribution and/or service (12b-1) fees | 0.25% | 1.00% | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% |
| Other expenses(c) | 0.16% | 0.16% | 0.08% | 0.16% | 0.13% | 0.08% | 0.16% |
| Acquired fund fees and expenses | 0.01% | 0.01% | 0.01% | 0.01% | 0.01% | 0.01% | 0.01% |
| Total annual Fund operating expenses(d) | 1.07% | 1.82% | 0.74% | 0.82% | 0.79% | 0.74% | 0.82% |
| (a) | This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions. |
| (b) | This charge applies to redemptions within 12 months after purchase, with certain limited exceptions. |
| (c) | Other expenses have been restated and are based on estimated amounts for the Fund's current fiscal year, taking into consideration changes in the method of allocating transfer agent expenses among Class A, Class C, Class R4 and Class Z shares of the Fund. |
| (d) | “Total annual Fund operating expenses” include acquired fund fees and expenses (expenses the Fund incurs indirectly through its investments in other investment companies) and may be higher than “Total Net Expenses” shown in the Financial Highlights section of this prospectus because “Total Net Expenses” do not include acquired fund fees and expenses. |
| 2. | The expense example table that appears under the caption “Fees and Expenses of the Fund – Example” in the “Summary of the Fund” section of the Prospectus and the Summary Prospectus is hereby superseded and replaced with the following: |
| 1 year | 3 years | 5 years | 10 years | |
| Class A (whether or not shares are redeemed) | $678 | $896 | $1,131 | $1,806 |
| Class C (assuming redemption of all shares at the end of the period) | $285 | $573 | $ 985 | $2,137 |
| Class C (assuming no redemption of shares) | $185 | $573 | $ 985 | $2,137 |
| Class I (whether or not shares are redeemed) | $ 76 | $237 | $ 411 | $ 918 |
| Class R4 (whether or not shares are redeemed) | $ 93 | $290 | $ 504 | $1,120 |
| Class R5 (whether or not shares are redeemed) | $ 81 | $252 | $ 439 | $ 978 |
| Class Y (whether or not shares are redeemed) | $ 76 | $237 | $ 411 | $ 918 |
| Class Z (whether or not shares are redeemed) | $ 84 | $262 | $ 455 | $1,014 |