SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

SCHEDULE 13D

INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT

TO RULE 13d-1(a) AND AMENDMENTS THERETO FILED PURSUANT TO

RULE 13d-2(a)

(Amendment No. 1)*

CRA International, Inc.

(Name of Issuer)

Common Stock

(Title of Class of Securities)

12618T105

(CUSIP Number)

Osmium Partners, LLC

300 Drakes Landing Road, Suite 172

Greenbrae, CA 94904

Attention: John H. Lewis

Telephone: (415) 785-4044

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

April 18, 2016

(Date of Event Which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of Rule 13d-1(e), 13d-1(f) or 13d-1(g), check the following box  ¨.

Note. Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See Rule 13d-7(b) for other parties to whom copies are to be sent.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes.)

EXPLANATORY NOTE

The Reporting Persons’ beneficial ownership has dropped below the 5% Schedule 13D reporting threshold. Therefore, this amendment No. 1 constitutes the final amendment to the Reporting Persons’ Schedule 13D and an exit filing for the Reporting Person and terminates the Reporting Persons’ obligation to further amend the Schedule 13D.

ITEM 3. Source and Amount of Funds or Other Consideration

Item 3 is hereby amended and restated in its entirety as follows:

The source and amount of funds (excluding commissions) used by the Funds in making their purchase of the shares of Common Stock, which includes Common Stock issuable upon the exercise of Options exercisable within 60 days (“Options”), owned by each of them in the aggregate was $9,433,930.66 from working capital.

One or more of the Reporting Persons effect purchases of securities through margin accounts which may extend margin credit to the Reporting Persons as and when required to open or carry positions in the margin accounts, subject to applicable federal margin regulations, stock exchange rules and brokers’ credit policies. In such instances, the positions held in the margin accounts are pledged as collateral security for the repayment of debit balances in the accounts.

ITEM 4. Purpose of Transaction

Item 4 is hereby amended and restated in its entirety as follows:

The Reporting Persons have acquired the Issuer’s Common Stock for investment purposes, and such purchases have been made in the Reporting Persons’ ordinary course of business.

In pursuing such investment purposes, the Reporting Persons may further purchase, hold, vote, trade, dispose or otherwise deal in the Common Stock at times, and in such manner, as they deem advisable to benefit from changes in market prices of such Common Stock, changes in the Issuer’s operations, business strategy or prospects, or from sale or merger of the Issuer. To

evaluate such alternatives, the Reporting Persons will routinely monitor the Issuer’s operations, prospects, business development, management, competitive and strategic matters, capital structure, and prevailing market conditions, as well as alternative investment opportunities, liquidity requirements of the Reporting Persons and other investment considerations. Consistent with its investment research methods and evaluation criteria, the Reporting Persons may discuss such matters with management or directors of the Issuer, other shareholders, industry analysts, existing or potential strategic partners or competitors, investment and financing professionals, sources of credit and other investors. Such factors and discussions may materially affect, and result in, the Reporting Persons’ modifying their ownership of the Issuer’s Common Stock, exchanging information with the Issuer pursuant to appropriate confidentiality or similar agreements, proposing changes in the Issuer’s operations, governance or capitalization, or in proposing one or more of the other actions described in subsections (a) through (j) of Item 4 of Schedule 13D.

The Reporting Persons reserve the right to formulate other plans and/or make other proposals, and take such actions with respect to their investment in the Issuer, including any or all of the actions set forth in paragraphs (a) through (j) of Item 4 of Schedule 13D, or acquire additional shares or dispose of all the shares beneficially owned by them, in the public market or privately negotiated transactions. The Reporting Persons may at any time reconsider and change their plans or proposals relating to the foregoing.

ITEM 5. Interest in Securities of the Issuer

Item 5 is hereby amended and restated in its entirety as follows:

(a) The Reporting Persons beneficially own:

Each Reporting Person disclaims beneficial ownership with respect to any shares of Common Stock other than the shares owned directly and of record by such Reporting Person.

The percentages set forth in this response are based on the 8,927,972 shares of Common Stock outstanding as of February 26, 2016, as reported by the Issuer in its Annual Report on Form 10-K for the fiscal year ended January 2, 2016 as filed with the SEC on March 4, 2016.

(b) Osmium Partners and Mr. Lewis may be deemed to share with Fund I, Fund II, Fund III and Fund IV (and not with any third party) the power to vote or direct the vote of and to dispose or direct the disposition of the 162,561 shares of Common Stock, 103,366 shares of Common Stock, 66,700 shares of Common Stock and 101,002 shares of Common Stock reported herein, respectively.

(c) The following Reporting Persons engaged in the following open-market transactions with respect to the Issuer’s Common Stock during the last 60 days:

Osmium Capital, LP

Osmium Capital II, LP

Osmium Spartan, LP

Osmium Diamond, LP

Other than the foregoing, no transactions in the Common Stock have been effected by the Reporting Persons in the last sixty (60) days.

(d) Not applicable.

(e) Not applicable.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, the undersigned certify that the information set forth in this statement is true, complete and correct.

Dated: April 20, 2016

EXHIBIT INDEX