The purpose of this supplement to the Statutory Prospectus dated February 28, 2026, as amended, of the ETF class shares of the portfolios listed above (each, a “Portfolio” and collectively, the “Portfolios”), each a series of DFA Investment Dimensions Group Inc. (the “Fund”), is to notify shareholders of the following changes.

The paragraph under the “Distribution-Distribution and Service (12B-1) FEES” section of the Prospectus is deleted in its entirety and replaced with the following:

The Board has adopted a distribution plan, sometimes known as a Rule 12b-1 plan, that allows a Portfolio’s ETF Class shares (excluding the ETF Class shares of the U.S. Targeted Value Portfolio, U.S. Core Equity 2 Portfolio and U.S. Small Cap Portfolio) to pay distribution fees of up to 0.25% per year, to those who sell and distribute ETF Class shares of the Portfolio and provide other services to shareholders. However, the Board has determined not to authorize payment of a Rule 12b-1 plan fee at this time. Because these fees are paid out of the assets of the ETF Class shares of a Portfolio on an ongoing basis, to the extent that a fee is authorized, over time these fees will increase the cost of your investment and may cost you more than paying other types of sales charges.