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                                                                    EXHIBIT 10.9

                      CLASS B NONVOTING COMMON STOCK OPTION

                               EXERCISE AGREEMENT

        THIS CLASS B NONVOTING COMMON STOCK OPTION EXERCISE AGREEMENT (this
"Agreement") is made effective as of May 31, 2001 by and between The Advisory
Board Company, a Maryland corporation (the "Company") and Michael A. D'Amato
(the "Optionee").

        WHEREAS, the Optionee has the option to purchase: (i) 625,000 shares of
Class B Nonvoting Common Stock, par value $0.01 per share (the "Class B Shares")
of the Company at a purchase price of $1.96, (ii) 75,000 shares of the Class B
Shares of the Company at a purchase price of $4.20 per share and (iii) 70,000
shares of the Class B Shares of the Company at a purchase price of $4.80 as set
forth in the various Stock Option Agreements attached as Exhibit A (the
"Options");

        WHEREAS, the Company has been appraised by Laird Square, LLC, as of
March 31, 2001 at a fair market value corresponding to $3.71 per Class B Share;

        WHEREAS, the Optionee has agreed to exercise the Options to acquire
770,000 Class B Shares, for a total purchase price equal to $1,876,000 on the
condition that the purchase price for the Shares will be paid in the form of an
interest-bearing Secured Promissory Note in the face amount equal to $1,876,000
to be executed in favor of the Company by the Optionee, substantially in the
form attached hereto as Exhibit B (the "Note"); and

        WHEREAS, the parties intend that Optionee will pledge the Shares to the
Company as security for the Note.

        NOW, THEREFORE, in consideration of the mutual promises and covenants
contained in this Agreement, the parties hereto agree as follows:

        1.      Exercise of Options. The Optionee hereby exercises the Option,
and, pursuant thereto, the Company hereby sells transfers and delivers to the
Optionee 770,000 Class B Shares (the "Shares"), duly endorsed for transfer to
the Optionee, in exchange for an aggregate purchase price of $1,876,000 payable
by the execution and delivery of the Note.

        2.      Execution and Delivery of Note. The Optionee hereby executes and
delivers the Note to the Company as payment in full for the Shares.

        3.      Pledge of Shares. The Optionee hereby grants to the Company a
first priority security interest in the Shares as provided in the Note.

        4.      Payment of Withholding Tax. Optionee agrees to pay to the
Company in full the total amount $453,083.00 in order to provide for the
withholding tax obligation of the Company associated with the exercise of the
Options.

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        5.      Representations of the Optionee.

                (a)     The Optionee has the legal right, power and authority to
execute and deliver this Agreement and to perform his obligations hereunder.
This Agreement constitutes the legal, valid and binding obligation of the
Optionee, enforceable against him in accordance with its terms (except as may be
limited by applicable bankruptcy, insolvency or other laws of general
applicability affecting creditors' rights and by general principles of equity,
whether such principles are considered at law or in equity).

                (b)     The Optionee acknowledges that, to the extent he is an
"affiliate" of the Company (as that term is defined in Rule 144 promulgated
under the Securities Act of 1933, as amended), or to the extent that the
Optionee is acquiring the Shares for his own account, for investment purposes
and not with a view to, or for sale in connection with, any distribution
thereof. The Optionee is an accredited investor within the definition set forth
in Rule 50 1(a) of the Securities Act of 1933, as amended. The Purchaser
understands that because the Shares have not been registered under the
Securities Act of 1933, as amended (the "Securities Act"), he cannot dispose of
any or all of the Shares unless such Shares are subsequently registered under
the Securities Act or exemptions from such registration are available. The
Purchaser understands that each certificate representing the Shares will bear
the following legend or one substantially similar thereto:

                These securities have not been registered under the Securities
                Act of 1933, as amended. They may not be sold, offered for sale,
                pledged or hypothecated in the absence of a registration
                statement in effect with respect to the securities under such
                Act or, except as otherwise determined by the Company, an
                opinion of counsel satisfactory to the Company that such
                registration is not required or unless sold pursuant to Rule 144
                of such Act.

                (c)     The Buyer is not required to make any filing with, or
obtain any permit, authorization or approval of, any governmental authority in
connection with the execution and delivery of this Agreement and the sale of
Shares contemplated hereby.

        6.      Survival of Representations and Warranties. All agreement,
representations and warranties contained herein shall survive the execution and
delivery of this Agreement and the Closing.

        7.      Miscellaneous.

                (a)     This Agreement may not be assigned by either party
without the consent of the other party (which consent shall not be unreasonably
withheld). This Agreement shall be binding upon and shall inure to the benefit
of the parties hereto and their respective heirs or successors in interest.

                (b)     This Agreement may be executed in one or more
counterparts, each of which shall for all purposes be deemed to be an original
and all of which shall constitute the same instrument.



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                (c)     Whenever possible, each provision of this Agreement will
be interpreted in such manner as to be effective and valid under applicable law,
but if any provision of this Agreement is held to be prohibited by or invalid
under applicable law, such provision will be ineffective only to the extent of
such prohibition or invalidity, without invalidating the remainder of such
provisions or the remaining provisions of this Agreement.

                (d)     This Agreement shall be construed in accordance with and
governed by the laws of the State of Delaware, without regard to Delaware
choice-of-law principles.

        IN WITNESS WHEREOF, the parties hereto have duly executed as of the day
and year first above written.



                                            THE ADVISORY BOARD COMPANY


                                            By: /s/ David G. Bradley
                                               -------------------------------
                                            Name: David G. Bradley
                                                 ----------------------------
                                            Title: Chairman
                                                  -----------------------------


                                            OPTIONEE:

                                            /s/Michael A. D'Amato
                                            ----------------------------------
                                               Michael A. D'Amato


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[THE ADVISORY BOARD COMPANY LETTERHEAD]


                                 July 30, 2001

Michael D'Amato
C/O The Advisory Board Company
600 New Hampshire Ave. NW
Washington, DC 20037

        Re:    May 31, 2001 exercise of stock options

Dear Michael,

        On May 31, 2001, you exercised options to purchase shares of the
Class B Non-voting Common Stock of The Advisory Board Company. For the purposes
of the documentation associated with this exercise of options, the number of
shares of stock issued to you was calculated based on our assumption that we had
completed a 25-to-one stock split effective as of January 2, 2001. We recently
discovered that this stock split was not properly completed. Therefore, the
number of shares of stock set forth in the documentation associated with your
May 31, 2001 exercise of stock options is incorrect. The actual number of shares
of stock you received from us on May 31, 2001 may be calculated by dividing the
number of shares of stock set forth in such documentation by 25. Because the
failure to complete the 25-to-one stock spilt had the same effect on all
stockholders and optionholders, the foregoing recalculation does not change your
relative ownership interest in the equity of The Advisory Board Company.

        Within the next few weeks, we plan to complete the 25-to-one stock
split which we originally intended to be effective as of January 2, 2001. After
the effective date of this stock split, the number of shares of stock issued
pursuant to your May 31, 2001 exercise of options will equal the number of
shares of stock originally set forth in the documentation associated with that
exercise of options.

        Please indicate your agreement with and acceptance of the terms of this
letter by executing and returning the enclosed duplicate copy of this letter.


                                          Very truly yours,

                                          /s/ DAVID FELSENTHAL
                                          ------------------------
                                          David Felsenthal
                                          Chief Financial Officer





Agreed and Accepted:


/s/ MICHAEL D'AMATO
-----------------------
Michael D'Amato