<PAGE>   1
                                                                   EXHIBIT 10.15

                           THE ADVISORY BOARD COMPANY
                              DIRECTORS' STOCK PLAN

1.      PURPOSE

        The purpose of The Advisory Board Company Directors' Stock Plan (the
        "Plan") is to advance the interests of The Corporate Executive Board
        Company, a Delaware corporation (hereinafter the "Company"), by enabling
        the Company to attract, retain and motivate qualified individuals to
        serve on the Company's Board of Directors and to align the financial
        interests of such individuals with those of the Company's stockholders
        by providing for or increasing their proprietary interest in the
        Company. Any stock options granted pursuant to this Plan shall not
        qualify under Section 422 of the Internal Revenue Code of 1986, as
        amended (the "Code"), as incentive stock options. The plan is intended
        to operate in a manner that exempts grants of Common Stock under the
        Plan from Section 16(b) of the Securities Exchange Act of 1934, as
        amended.

2.      DEFINITIONS

        (a) "Board" means the Board of Directors of the Company.

        (b) "Committee" means the Board and/or the Compensation Committee of the
        Board acting pursuant to its authorization to administer this Plan under
        Section 7.

        (c) "Common Stock" means the Company's Class B Non-Voting Common Stock,
        par value $.01 per share, subject to adjustment as provided in Section
        9.

        (d) "Market Value" means, as of any date, and unless the Committee shall
        specify otherwise, the closing sale price of the Common Stock as
        reported for such date pursuant to the consolidated quotation system or
        any other transaction reporting plan under Section 11A of the Securities
        Exchange Act of 1934, as amended (the "Exchange Act"), or, if there have
        been no sales so reported for such date, the average of the best bid and
        best offer prices quoted under the consolidated quotation system or any
        other such transaction reporting plan as of 4:00 p.m., New York time, on
        such date, or if on any date the Common Stock is not so quoted, the
        average of the best bid and best offered prices on such day in the
        domestic over-the-counter market as reported by the National Quotation
        Bureau, Incorporated, or any similar successor or comparable
        organization. If at any time the Common Stock is not listed on any
        domestic securities exchange or quoted under a transaction reporting
        plan or in the domestic over-the-counter market, the "Market Value"
        shall be the fair value thereof determined by the Committee.

        (e) "Options" shall mean the stock options granted to a Participant with
        respect to shares of Common Stock pursuant to the terms of this Plan.

        (f) "Stock Grant" shall mean the award of shares of Common Stock to a
        Participant pursuant to the terms of this Plan.






                                       1
<PAGE>   2

3.      SHARES SUBJECT TO THE PLAN

        Subject to adjustment as provided in Section 9, the maximum number of
        shares of Common Stock which may be issued pursuant to this Plan shall
        not exceed 900,000. Shares issued under this Plan may be authorized and
        unissued shares of Common Stock or shares of Common Stock reacquired by
        the Company. All or any shares of Common Stock subject to an Option or a
        Stock Grant which for any reason are not issued, do not become vested or
        are reacquired pursuant to the Plan or the terms of an Option or Stock
        Grant may again be made subject to an Option or Stock Grant under the
        Plan.

4.      PARTICIPANTS

        Any person who is, or is elected to be, a director of the Company or any
        of its subsidiaries shall be eligible for the award of Options and/or
        Stock Grants hereunder. The Committee shall determine to which directors
        any such Options and/or Stock Grants shall be awarded hereunder (any
        such director and his or her authorized transferees hereinafter referred
        to as a "Participant").

5.      DIRECTOR AWARDS

        The Committee may provide for Options and/or Stock Grants to be awarded
        to Directors in consideration for their service to the Company. The
        Committee shall specify the number of shares subject to each Option or
        Stock Grant provided for under this Section 5, or the formula pursuant
        to which such number shall be determined, the Participants to receive
        any such award, the date of award and the vesting and expiration terms
        applicable to such Option or Stock Grant. The award of Options or Stock
        Grants hereunder may, but need not, be conditioned on the Director
        electing to forego his or her right to all or any part of his or her
        cash retainer or other fees. Subject to adjustment pursuant to Section
        9, the maximum number of shares of Common Stock subject to Options and
        Stock Grants awarded under this Plan during any calendar year to any
        person on account of his or her service as a director shall not exceed
        100,000 shares.

6.      TERMS AND CONDITIONS OF OPTIONS AND STOCK GRANTS

        (a) General Terms and Conditions: Options and Stock Grants awarded
        pursuant to the Plan need not be identical but each Option and Stock
        Grant shall be subject to the following general terms and conditions:

                (1) Terms and Restrictions Upon Shares: The Committee may
                provide that the shares of Common Stock issued upon exercise of
                an Option or receipt of a Stock Grant shall be subject to such
                further conditions, restrictions or agreements as the Committee
                in its discretion may specify prior to the exercise of such
                Option or receipt of such Stock Grant, including without
                limitation, manner of sale, deferrals on issuance, conditions on
                vesting or transferability, and forfeiture or repurchase
                provisions.

                (2) Transferability: Unless otherwise provided by the Committee,
                awards of Options or Stock Grants under the Plan shall be
                nontransferable by the Participant other than by will or the
                laws of descent and distribution and Options shall be
                exercisable only by the Participant during his or her lifetime.






                                       2
<PAGE>   3

                (3) Other Terms and Conditions: No holder of an Option or Stock
                Grant shall have any rights as a stockholder with respect to any
                shares of Common Stock subject to an Option or Stock Grant
                hereunder until said shares have been issued. Options and Stock
                Grants may also contain such other provisions, which shall not
                be inconsistent with any of the foregoing terms, as the
                Committee shall deem appropriate. The Committee may waive
                conditions to and/or accelerate exercisability of an Option or
                Stock Grant, either automatically upon the occurrence of
                specified events (including in connection with a change of
                control of the Company) or otherwise in its discretion. No
                Option or Stock Grant, however, nor anything contained in the
                Plan, shall confer upon any Participant any right to serve as a
                director of the Company or any of its subsidiaries.

        (b) Option Terms: The Committee may establish the terms, provisions and
        conditions applicable to awards of Options (including, but not limited
        to, exercise price, exercisability and vesting) to the extent such
        terms, provisions and conditions are consistent with the express
        provisions of the Plan. The exercise price for each Option shall be
        established by the Committee or under a formula established by the
        Committee. Notwithstanding the forgoing, the exercise price shall not be
        less than the Market Value of the Common Stock on the date of grant of
        the Option, unless the Participant pays or foregoes compensation in the
        amount of any discount. The exercise price of an Option shall be payable
        (i) in cash, (ii) by payment under an arrangement with a broker where
        payment is made pursuant to an irrevocable direction to the broker to
        deliver all or part of the proceeds from the sale of the Option shares
        to the Company, (iii) by tendering (either physically or by attestation)
        shares of Common Stock owned by the Participant exercising the Option
        and having a Market Value on the date of exercise equal to the exercise
        price but only if such will not result in an accounting charge to the
        Company, or (iv) by any combination of the foregoing. In addition, the
        exercise price may be payable in such other form(s) of consideration as
        the Committee in its discretion shall specify, including without
        limitation by loan (as described in Section 8) or by techniques that may
        result in an accounting charge to the Company.

        (c) Stock Grant Terms: Stock Grants under the Plan may, in the sole
        discretion of the Committee, but need not, be conditioned upon the
        Participant paying cash or cash-equivalent consideration or agreeing to
        forego other compensation for the shares of Common Stock covered by the
        Stock Grant. Stock Grants under the Plan may be subject to terms,
        provisions and conditions (including, but not limited to, vesting) as
        are established in the sole discretion of the Committee, provided such
        terms, provisions and conditions are consistent with the express
        provisions of the Plan. The terms, provisions and conditions may be
        contingent upon the passage of time, continued service or achievement of
        Company or individual performance goals, as specified by the Committee.

7.      ADMINISTRATION OF THE PLAN

        The Plan shall be administered by the Board, except to the extent the
        Board designates that the Plan shall be administered by the Compensation
        Committee of the Board (the Board or any such designated committee, the
        "Committee"). The Committee shall act pursuant to a majority vote or
        unanimous written consent.




                                       3
<PAGE>   4

        Subject to the express provisions of this Plan, the Committee shall be
        authorized and empowered to do all things necessary or desirable in
        connection with the administration of this Plan, including, without
        limitation: (a) to prescribe, amend and rescind rules relating to this
        Plan and to define terms not otherwise defined herein; (b) to prescribe
        the form of documentation used to evidence any Option or Stock Grant
        awarded hereunder, including provision for such terms as it considers
        necessary or desirable, not inconsistent with the terms established by
        the Committee; (c) to establish and verify the extent of satisfaction of
        any conditions to exercisability applicable to Options or to receipt or
        vesting of Stock Grants; (d) to determine whether, and the extent to
        which, adjustments are required pursuant to Section 9 hereof; and (e) to
        interpret and construe this Plan, any rules and regulations under the
        Plan and the terms and conditions of any Option or Stock Grant awarded
        hereunder, and to make exceptions to any procedural provisions in good
        faith and for the benefit of the Company.

        All decisions, determinations and interpretations by the Committee
        regarding the Plan, any rules and regulations under the Plan and the
        terms and conditions of any Option or Stock Grant awarded hereunder,
        shall be final and binding on all Participants and holders of Options
        and Stock Grants. The Committee may consider such factors as it deems
        relevant, in its sole and absolute discretion, in making such decisions,
        determinations and interpretations including, without limitation, the
        recommendations or advice of any officer or other employee of the
        Company and such attorneys, consultants and accountants as it may
        select.

8.      LOANS

        The Company may, if authorized by the Committee, make loans for the
        purpose of enabling a Participant to exercise Options and, if
        applicable, receive Common Stock awarded under the Plan and to pay the
        tax liability resulting from an Option exercise or Stock Grant under the
        Plan. The Committee shall have full authority to determine the terms and
        conditions of such loans. Such loans may be secured by the shares of
        Common Stock received upon exercise of such Option or receipt of such
        Stock Grant.

9.      ADJUSTMENT OF AND CHANGES IN THE STOCK

        If the outstanding securities of the class then subject to this Plan are
        increased, decreased or exchanged for or converted into cash, property
        or a different number or kind of shares or securities, or if cash,
        property or shares or securities are distributed in respect of such
        outstanding securities, in either case as a result of a reorganization,
        reclassification, dividend (other than a regular, quarterly cash
        dividend or an issuance of the class of securities then subject to this
        Plan as part of a public or private offering thereof) or other
        distribution, stock split, reverse stock split, spin-off or the like, or
        if substantially all of the property and assets of the Company are sold,
        then, unless the terms of such transaction shall provide otherwise, the
        maximum number and type of shares or other securities that may be issued
        under this Plan shall be appropriately adjusted. The Committee shall
        determine in its sole discretion the appropriate adjustment, if any, to
        be effected pursuant to the immediately preceding sentence. In addition,
        in connection with any such change in the class of securities then
        subject to this Plan, the Committee may make appropriate and
        proportionate adjustments in the number and type of shares or other
        securities or cash or other property that may be acquired pursuant to
        Options and Stock Grants theretofore







                                       4
<PAGE>   5

        awarded under this Plan and the exercise price of such Options or price,
        if any, of such Stock Grants.

        No right to purchase or receive fractional shares shall result from any
        adjustment in Options or Stock Grants pursuant to this Section 9. In
        case of any such adjustment, the shares subject to the Option or Stock
        Grant shall be rounded up to the nearest whole share of Common Stock.

10.     REGISTRATION, LISTING OR QUALIFICATION OF STOCK

        In the event that the Committee determines in its discretion that the
        registration, listing or qualification of the shares of Common Stock
        issuable under the Plan on any securities exchange or under any
        applicable law or governmental regulation is necessary as a condition to
        the issuance of such shares under the Option or Stock Grant, the Option
        or Stock Grant shall not be exercisable or exercised in whole or in part
        unless such registration, listing, qualification, consent or approval
        has been unconditionally obtained.

11.     TAXES

        The Committee may make such provisions or impose such conditions as it
        may deem appropriate for the withholding or payment by a Participant of
        any taxes which it determines are necessary or appropriate in connection
        with any issuance, exercise or vesting of any Options, Stock Grants or
        shares under this Plan, and the rights of a holder of an Option or Stock
        Grant or shares are subject to satisfaction of such conditions. The
        Company shall not be required to issue shares of Common Stock or to
        recognize the disposition of such shares until such obligations are
        satisfied. At the Participant's election, any such obligations may be
        satisfied by having the Company withhold a portion of the shares of
        Common Stock that otherwise would be issued to the holder of the Option
        or Stock Grant upon exercise of the Option or vesting or receipt of the
        Stock Grant or by surrendering to the Company shares of Common Stock
        previously acquired, provided that such will not result in an accounting
        charge to the Company. The Company and any affiliate of the Company
        shall not be liable to a Participant or any other persons as to any tax
        consequence expected, but not realized, by any Participant or other
        person due to the receipt of any Options or shares awarded hereunder.

12.     GOVERNING LAW

        The Plan and any agreements or other documents hereunder shall be
        interpreted and construed in accordance with the laws of the District of
        Columbia and applicable federal law. Any reference in this Plan or in
        the agreement or other document evidencing any Options to a provision of
        law or to a rule or regulation shall be deemed to include any successor
        law, rule or regulation of similar effect or applicability.

13.     ARBITRATION OF DISPUTES

        In the event a Participant or other holder of an Option believes that a
        decision by the Administrator with respect to such person was arbitrary
        or capricious, the Participant or optionholder may request arbitration
        with respect to such decision. The review by the arbitrator shall be
        limited to determining whether the Administrator's decision was
        arbitrary or capricious. This arbitration shall be the sole and
        exclusive review permitted of







                                       5
<PAGE>   6

        the Administrator's decision. Participants and optionholders explicitly
        waive any right to judicial review.

        Notice of demand for arbitration shall be made in writing to the
        Administrator within thirty (30) days after the applicable decision by
        the Administrator. Any such arbitration shall be heard in the District
        of Columbia, before a panel consisting of one arbitrator. Except as the
        parties to the arbitration may otherwise agree, the arbitrator shall be
        appointed in the first instance by the appropriate official in the
        District of Columbia office of the American Arbitration Association or,
        in the event of his or her unavailability by reason of disqualification
        or otherwise, by the appropriate official in the New York City office of
        the American Arbitration Association. The arbitrator and shall be an
        individual who is an attorney licensed to practice law in the District
        of Columbia. Such arbitrator shall be neutral within the meaning of the
        Commercial Rules of Dispute Resolution of the American Arbitration
        Association; provided, however, that the arbitration shall not be
        administered by the American Arbitration Association. Any challenge to
        the neutrality of the arbitrator shall be resolved by the arbitrator
        whose decision shall be final and conclusive. The arbitration shall be
        administered and conducted by the arbitrator pursuant to the Commercial
        Rules of Dispute Resolution of the American Arbitration Association. The
        decision of the arbitrator on the issue(s) presented for arbitration
        shall be final and conclusive and may be enforced in any court of
        competent jurisdiction.

14.     EFFECTIVE DATE, AMENDMENT AND TERMINATION OF PLAN

        This Plan was adopted by the Board of Directors and approved by the
        stockholders of the Company on June 1, 2001 (the "Effective Date"). Any
        Options and Stock Grants awarded prior to the such date shall be
        contingent on such approval and, if such approval is not obtained, shall
        be null and of no effect.

        The Plan shall remain available for the grant of Options and Stock
        Grants until the tenth anniversary of the Effective Date. The Board may
        periodically amend the Plan as it determines appropriate, without
        further action by the Company's stockholders except to the extent
        required by applicable law. Any amendment to the Plan will not affect
        the rights and obligations arising under Options or Stock Grants
        theretofore awarded and then in effect. Notwithstanding the foregoing,
        and subject to adjustment pursuant to Section 9, the Plan may not be
        amended to increase the number of shares of Common Stock authorized for
        issuance under the Plan, unless any such amendment is approved by the
        Company's stockholders. The Plan may be earlier terminated at such
        earlier time as the Board may determine. Termination and expiration of
        the Plan will not affect the rights and obligations arising under
        Options or Stock Grants theretofore awarded and then in effect.






                                       6