DFA INVESTMENT DIMENSIONS GROUP INC.

	Class:	Ticker:	Exchange:
U.S. Micro Cap Portfolio	ETF Class shares	DFMC	NYSE Arca, Inc.

Summary Prospectus

January 7, 2026

Before you invest, you may want to review the Portfolio’s ETF Class shares Prospectus, which contains more information about the Portfolio and its risks. You can find the Portfolio’s ETF Class shares Prospectus and other information about the Portfolio, including the Statement of Additional Information (SAI) and most recent reports to shareholders, when available, online at https://www.dimensional.com/us-en/document-center. You can also get this information at no cost by calling collect to (512) 306-7400 or by sending an e-mail request to document_requests@dimensional.com. The Portfolio’s ETF Class shares Prospectus and SAI, both dated January 7, 2026, as may be supplemented, are incorporated by reference into this Summary Prospectus.

Investment Objective

The investment objective of the U.S. Micro Cap Portfolio (the “Portfolio”) is to achieve long-term capital appreciation.

Fees and Expenses of the Portfolio

This table describes the fees and expenses you may pay if you buy, hold or sell ETF Class shares of the Portfolio. You may also incur usual and customary brokerage commissions when buying or selling the ETF Class shares of the Portfolio, which are not reflected in the table or Example that follows.

Shareholder Fees (fees paid directly from your investment): None
Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Management Fee	0.38%
Other Expenses1	0.05%
Total Annual Fund Operating Expenses	0.43%
Fee Waiver and/or Expense Reimbursement2	0.02%
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement	0.41%

1

The ETF Class shares of the Portfolio are new, so the “Other Expenses" shown for the class are based on anticipated fees and expenses for the first full fiscal year.

2

Dimensional Fund Advisors LP (the “Advisor”) has agreed to waive certain fees and in certain instances, assume certain expenses of the ETF Class shares of the Portfolio. The Fee Waiver and/or Expense Assumption Agreement for the Portfolio will remain in effect through February 28, 2027, and may only be terminated by the Fund’s Board of Directors prior to that date. Under certain circumstances, the Advisor retains the right to seek reimbursement for any fees previously waived and/or expenses previously assumed up to thirty-six months after such fee waiver and/or expense assumption.

EXAMPLE

This Example is meant to help you compare the cost of investing in the Portfolio's ETF Class shares with the cost of investing in other funds. The Example assumes that you invest $10,000 in the Portfolio's ETF Class shares for the time periods indicated. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. The costs for the Portfolio's ETF Class shares reflect the net expenses of the Portfolio's ETF Class shares that result from the contractual expense waiver in the first year only. Although your actual costs may be higher or lower, based on these assumptions your costs whether you redeem or hold your shares would be:

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1 Year	3 Years	5 Years	10 Years
$42	$136	$239	$540

PORTFOLIO TURNOVER

A fund generally pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Portfolio’s performance. During the fiscal year ended October 31, 2024, the Portfolio's portfolio turnover rate was 9% of the average value of its investment portfolio.

Principal Investment Strategies

To achieve the U.S. Micro Cap Portfolio’s investment objective, the Advisor implements an integrated investment approach that combines research, portfolio design, portfolio management, and trading functions. As further described below, the Portfolio’s design emphasizes long-term drivers of expected returns identified by the Advisor’s research, while balancing risk through broad diversification across companies and sectors. The Advisor’s portfolio management and trading processes further balance those long-term drivers of expected returns with shorter-term drivers of expected returns and trading costs.

The U.S. Micro Cap Portfolio, using a market capitalization weighted approach, is designed to purchase a broad and diverse group of the securities of U.S. micro cap companies. A company’s market capitalization is the number of its shares outstanding times its price per share. Under a market capitalization weighted approach, companies with higher market capitalizations generally represent a larger proportion of the Portfolio than companies with relatively lower market capitalizations. The Portfolio may emphasize certain stocks, including smaller capitalization companies, lower relative price stocks, and/or higher profitability stocks as compared to their representation in the micro-cap segment of the U.S. market. An equity issuer is considered to have a low relative price (i.e., a value stock) primarily because it has a low price in relation to its book value. In assessing relative price, the Advisor may consider additional factors such as price to cash flow or price to earnings ratios. An equity issuer is considered to have high profitability because it has high earnings or profits from operations in relation to its book value or assets. The criteria the Advisor uses for assessing relative price and profitability are subject to change from time to time.

As a non-fundamental policy, under normal circumstances, the U.S. Micro Cap Portfolio will invest at least 80% of its net assets in securities of U.S. micro cap companies. The Advisor generally defines a U.S. company as one that is listed and principally traded on a securities exchange in the United States that is deemed

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appropriate by the Advisor. As of the date of this Prospectus, for the purposes of the Portfolio, the Advisor considers micro cap companies to be companies whose market capitalizations are generally in the lowest 5% of total market capitalization or companies whose market capitalizations are smaller than the 1,500th largest U.S. company, whichever results in the higher market capitalization break. Total market capitalization is based on the market capitalization of eligible U.S. operating companies listed on a securities exchange in the United States that is deemed appropriate by the Advisor. Under the Advisor’s market capitalization guidelines described above, based on market capitalization data as of October 31, 2025, the market capitalization of a micro cap company would be below $7,001 million. This threshold will change due to market conditions.

The Advisor may also increase or reduce the U.S. Micro Cap Portfolio’s exposure to an eligible company, or exclude a company, based on shorter-term considerations, such as a company’s price momentum, short-run reversals, and investment characteristics. In assessing a company’s investment characteristics, the Advisor considers ratios such as recent changes in assets divided by total assets. The criteria the Advisor uses for assessing a company’s investment characteristics are subject to change from time to time. In addition, the Advisor seeks to reduce trading costs using a flexible trading approach that looks for opportunities to participate in the available market liquidity, while managing turnover and explicit transaction costs.

The U.S. Micro Cap Portfolio may purchase or sell futures contracts and options on futures contracts for U.S. equity securities and indices to increase or decrease equity market exposure based on actual or expected cash inflows to or outflows from the Portfolio.

The U.S. Micro Cap Portfolio may lend its portfolio securities to generate additional income.

The U.S. Micro Cap Portfolio's ETF Class operates as an actively managed exchange-traded fund ("ETF") and does not seek to replicate the performance of a specific index and may have a higher degree of portfolio turnover than passively managed index ETFs.

Principal Risks

Because the value of your investment in the Portfolio will fluctuate, there is the risk that you will lose money. An investment in the Portfolio is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The following is a description of principal risks of investing in the Portfolio.

Equity Market Risk:Even a long-term investment approach cannot guarantee a profit. Economic, market, political, and issuer-specific conditions and events will cause the

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value of equity securities, and a fund that owns them, to rise or fall. Stock markets are volatile, with periods of rising prices and periods of falling prices.

Small Company Risk: Securities of small companies are often less liquid than those of large companies and this could make it difficult to sell a small company security at a desired time or price. As a result, small company stocks may fluctuate relatively more in price. In general, smaller capitalization companies are also more vulnerable than larger companies to adverse business or economic developments and they may have more limited resources.

Profitability Investment Risk: High relative profitability stocks may perform differently from the market as a whole and an investment strategy purchasing these securities may cause a fund to at times underperform equity funds that use other investment strategies.

Value Investment Risk:Value stocks may perform differently from the market as a whole and an investment strategy purchasing these securities may cause a fund to at times underperform equity funds that use other investment strategies. Value stocks can react differently to political, economic, and industry developments than the market as a whole and other types of stocks. Value stocks also may underperform the market for long periods of time.

Derivatives Risk: Derivatives are instruments, such as futures contracts, and options thereon, whose value is derived from that of other assets, rates or indices. The use of derivatives for non-hedging purposes may be considered to carry more risk than other types of investments. When a fund uses derivatives, the fund will be directly exposed to the risks of those derivatives. Derivative instruments are subject to a number of risks including counterparty, liquidity, interest rate, market, credit and management risks, as well as the risk of improper valuation. Changes in the value of a derivative may not correlate perfectly with the underlying asset, rate or index, and a fund could lose more than the principal amount invested.

Securities Lending Risk: Securities lending involves the risk that the borrower may fail to return the securities in a timely manner or at all. As a result, a fund may lose money and there may be a delay in recovering the loaned securities. A fund could also lose money if it does not recover the securities and/or the value of the collateral falls, including the value of investments made with cash collateral. Securities lending also may have certain adverse tax consequences.

Operational Risk:Operational risks include human error, changes in personnel, system changes, faults in communication, and failures in systems, technology, or processes. Various operational events or circumstances are outside a fund’s or its advisor’s control, including instances at third parties. A fund and its advisor seek to reduce these operational risks through controls and procedures. However, measures that seek to reduce these operational risks through controls and procedures may not address every possible risk and may be inadequate to address these risks.

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Cyber Security Risk:A fund and its service providers’ use of internet, technology and information systems may expose the fund to potential risks linked to cyber security breaches of those technological or information systems. Cyber security breaches, amongst other things, could allow an unauthorized party to gain access to proprietary information, customer data, or fund assets, or cause the fund and/or its service providers to suffer data corruption or lose operational functionality.

The following is a description of additional principal risks of investing in the ETF Class shares of the Portfolio, due to the shares being listed and traded on a national securities exchange.

Market Trading Risk:Active trading markets for the ETF Class shares may not be developed or maintained by market makers or authorized participants. Authorized participants are not obligated to make a market in the ETF Class shares or to submit purchase or redemption orders for creation units, which may widen bid-ask spreads. Trading in shares on an exchange may be halted in certain circumstances. There can be no assurance that the requirements of the listing exchange necessary to maintain the listing of the ETF Class shares will continue to be met. Additionally, in stressed market conditions, the market for the ETF Class shares may become less liquid in response to deteriorating liquidity in the markets for a fund’s portfolio holdings, which may cause a significant variance in the market price of the ETF Class shares and their underlying value as well as an increase in the ETF Class shares’ bid-ask spread.

Premium/Discount Risk:The net asset value (“NAV”) of the ETF Class shares and the value of your investment may fluctuate. Disruptions to creations and redemptions or the market price of a fund’s holdings, the existence of extreme market volatility or potential lack of an active trading market for shares may widen bid-ask spreads and result in shares trading at a significant premium or discount to NAV. If a shareholder purchases shares at a time when the market price is at a premium to the NAV or sells shares at a time when the market price is at a discount to the NAV, the shareholder may sustain losses.

Performance

The bar chart and table immediately following illustrate the variability of the Portfolio’s returns and are meant to provide some indication of the risks of investing in the Portfolio. The ETF Class shares of the Portfolio are a new class of shares for which performance information is not available, and therefore, for periods prior to the inception of the ETF Class shares, the bar chart and table show performance information for the Institutional Class shares of the Portfolio, a mutual fund class of shares of the Portfolio not offered in this Prospectus. Returns of the ETF Class shares of the Portfolio may vary from the returns of the Institutional Class shares due to differences in expenses. The bar chart shows the changes in performance of the Institutional Class shares of the Portfolio from year to year. The table illustrates how annualized returns of the Institutional Class shares of the Portfolio for certain periods, both before and after taxes,compare with those of a broad measure of market performance. The table also includes the performance of an additional index with a

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similar investment universe as the Portfolio. The Portfolio’s past performance (before and after taxes) is not an indication of future results. Updated performance information for the Portfolio can be obtained by visiting https://www.dimensional.com/us-en/funds.

The after-tax returns presented in the table for the Portfolio are calculated using the historical highest individual federal marginal 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 in the table. In addition, the after-tax returns shown are not relevant to investors who hold shares of the Portfolio through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts.

U.S. Micro Cap Portfolio Institutional Class Shares¹ —Total Returns

January 2015-December 2024
Highest Quarter	Lowest Quarter
30.59% 2020, Q4	-34.75% 2020, Q1

Year-to-date returns as of September 30, 2025: 7.16%

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Annualized Returns (%) Periods ended December 31, 2024
		1 Year	5 Years	10 Years
U.S. Micro Cap Portfolio - Institutional Class Shares
	Return Before Taxes	11.42%	10.35%	8.92%
	Return After Taxes on Distributions	11.16%	9.31%	7.77%
	Return After Taxes on Distributions and Sale of Portfolio Shares	6.94%	8.07%	6.98%
Russell 2000® Index
(reflects no deduction for fees, expenses or taxes)		11.54%	7.40%	7.82%
Russell 3000® Index
(reflects no deduction for fees, expenses or taxes)		23.81%	13.86%	12.55%
1.	As of December 31, 2024, the ETF Class shares of the Portfolio had not yet incepted. Performance shown prior to the inception date of the ETF Class shares is from the Portfolio's Institutional Class shares, a mutual fund class of shares of the Portfolio not offered in this Prospectus. Returns for the ETF Class shares and Institutional Class shares may vary due to differences in their expenses.

Investment Advisor/Portfolio Management

Dimensional Fund Advisors LP serves as the investment advisor for the Portfolio. The following individuals are responsible for leading the day-to-day management of the Portfolio:

•Jed S. Fogdall, Global Head of Portfolio Management, Chairman of the Investment Committee, Vice President, and Senior Portfolio Manager of the Advisor, has been a portfolio manager of the Portfolio since 2012.

•Joel P. Schneider, Deputy Head of Portfolio Management, North America, member of the Investment Committee, Vice President, and Senior Portfolio Manager of the Advisor, has been a portfolio manager of the Portfolio since 2015.

•Marc C. Leblond, Vice President and Senior Portfolio Manager of the Advisor, has been a portfolio manager of the Portfolio since 2020.

Purchase and Sale of Shares

The Portfolio issues (or redeems) ETF Class shares at NAV only to certain financial institutions that have entered into agreements with the Portfolio’s distributor in large aggregated blocks known as “Creation Units.” A Creation Unit of the Portfolio’s ETF Class shares consists of 25,000shares. Creation Units are issued (or redeemed) in-kind for securities (and an amount of cash) that the Portfolio specifies each day at the NAV next determined after receipt of an order.

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Individual ETF Class shares of the Portfolio may only be purchased and sold on NYSE Arca, Inc., other national securities exchanges, electronic crossing networks and other alternative trading systems through your broker-dealer at market prices and are not individually redeemable from the Portfolio. An investor may incur costs attributable to the difference between the highest price a buyer is willing to pay to purchase shares (bid) and the lowest price a seller is willing to accept for shares (ask) when buying or selling shares in the secondary market (the “bid-ask spread”). Because the Portfolio’s ETF Class shares trade at market prices rather than at NAV, ETF Class shares may trade at a price less than (discount) or greater than (premium) the NAV of the ETF Class shares. Recent information, including information on the ETF Class shares’ NAV, market price, premiums and discounts, and bid-ask spreads, is available on the Portfolio’s website at https://www.dimensional.com/us-en/funds.

Tax Information

The dividends and distributions you receive from the Portfolio are taxable and generally will be taxed as ordinary income, capital gains, or some combination of both, unless you are investing through a tax-advantaged arrangement, such as a 401(k) plan or an individual retirement account, in which case distributions may be taxed as ordinary income when withdrawn from the plan or account.

Payments to Financial Intermediaries

If you purchase the Portfolio through a broker-dealer or other financial intermediary (such as a bank), the Portfolio and its related companies may pay the intermediary for the sale of the Portfolio shares and/or related services. These payments may create a conflict of interest by influencing the financial intermediary to recommend the Portfolio over another investment. Ask your financial advisor or visit your financial intermediary’s website for more information.

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Dimensional Fund Advisors LP 6300 Bee Cave Road, Building One Austin, TX 78746 (512) 306-7400
DFA-010726-DFMC