UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                  SCHEDULE 13G

                    Under the Securities Exchange Act of 1934
                               (Amendment No. 6)*

                             SEI INVESTMENTS COMPANY
                                (Name of Issuer)

                          Common Stock, $.01 par value
                         (Title of Class of Securities)

                                   784117 10 3
                                 (CUSIP Number)

                                December 31, 2003
             (Date of Event which Requires filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule
is filed:

|_|   Rule 13d-1(b)
|X|   Rule 13d-1(c)
|_|   Rule 13d-1(d)

* The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter the
disclosures provided in a prior cover page.

The information required in 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 ("Act") 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).



CUSIP No. 784117 10 3

--------------------------------------------------------------------------------
1     NAMES OF REPORTING PERSONS
      I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (entities only)

      Thomas W. Smith
--------------------------------------------------------------------------------
2     CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP                   (a) |_|
                                                                         (b) |X|

--------------------------------------------------------------------------------
3     SEC USE ONLY

--------------------------------------------------------------------------------
4     CITIZEN OR PLACE OF ORGANIZATION

      United States
--------------------------------------------------------------------------------
                      5     SOLE VOTING POWER

     NUMBER OF              1,948,624
      SHARES          ----------------------------------------------------------
   BENEFICIALLY       6     SHARED VOTING POWER
   OWNED BY EACH
     REPORTING              5,755,014
      PERSON          ----------------------------------------------------------
       WITH           7     SOLE DISPOSITIVE POWER

                            1,948,624
                      ----------------------------------------------------------
                      8     SHARED DISPOSITIVE POWER

                            5,755,014
--------------------------------------------------------------------------------
9     AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

      7,703,638
--------------------------------------------------------------------------------
10    CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES

      Not Applicable
--------------------------------------------------------------------------------
11    PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

      7.3%
--------------------------------------------------------------------------------
12    TYPE OF REPORTING PERSON

      IN
--------------------------------------------------------------------------------


                                     - 2 -


CUSIP No. 784117 10 3

--------------------------------------------------------------------------------
1     NAMES OF REPORTING PERSONS
      I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (entities only)

      Thomas N. Tryforos
--------------------------------------------------------------------------------
2     CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP                   (a) |_|
                                                                         (b) |X|

--------------------------------------------------------------------------------
3     SEC USE ONLY

--------------------------------------------------------------------------------
4     CITIZEN OR PLACE OF ORGANIZATION

      United States
--------------------------------------------------------------------------------
                      5     SOLE VOTING POWER

     NUMBER OF              7,336
      SHARES          ----------------------------------------------------------
   BENEFICIALLY       6     SHARED VOTING POWER
   OWNED BY EACH
     REPORTING              5,755,014
      PERSON          ----------------------------------------------------------
       WITH           7     SOLE DISPOSITIVE POWER

                            7,336
                      ----------------------------------------------------------
                      8     SHARED DISPOSITIVE POWER

                            5,755,014
--------------------------------------------------------------------------------
9     AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

      5,762,350
--------------------------------------------------------------------------------
10    CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES

      Not Applicable
--------------------------------------------------------------------------------
11    PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

      5.5%
--------------------------------------------------------------------------------
12    TYPE OF REPORTING PERSON

      IN
--------------------------------------------------------------------------------


                                     - 3 -


CUSIP No. 784117 10 3

--------------------------------------------------------------------------------
1     NAMES OF REPORTING PERSONS
      I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (entities only)

      Scott J. Vassalluzo
--------------------------------------------------------------------------------
2     CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP                   (a) |_|
                                                                         (b) |X|

--------------------------------------------------------------------------------
3     SEC USE ONLY

--------------------------------------------------------------------------------
4     CITIZEN OR PLACE OF ORGANIZATION

      United States
--------------------------------------------------------------------------------
                      5     SOLE VOTING POWER

     NUMBER OF              0
      SHARES          ----------------------------------------------------------
   BENEFICIALLY       6     SHARED VOTING POWER
   OWNED BY EACH
     REPORTING              5,755,014
      PERSON          ----------------------------------------------------------
       WITH           7     SOLE DISPOSITIVE POWER

                            0
                      ----------------------------------------------------------
                      8     SHARED DISPOSITIVE POWER

                            5,755,014
--------------------------------------------------------------------------------
9     AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

      5,755,014
--------------------------------------------------------------------------------
10    CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES

      Not Applicable
--------------------------------------------------------------------------------
11    PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

      5.5%
--------------------------------------------------------------------------------
12    TYPE OF REPORTING PERSON

      IN
--------------------------------------------------------------------------------


                                     - 4 -


ITEM 1.     (a)   Name of Issuer:

                  SEI Investments Company

            (b)   Address of Issuer's Principal Executive Offices:

                  1 Freedom Valley Drive
                  Oaks, PA 19456-1100

ITEM 2.     (a)   Name of Person Filing:

                  (i)   Thomas W. Smith

                  (ii)  Thomas N. Tryforos

                  (iii) Scott J. Vassalluzo

                  The filing of this Statement shall not be deemed to be an
                  admission that the filing persons comprise a "group" within
                  the meaning of Section 13(d)(3) of the Securities Exchange Act
                  of 1934, as amended.

            (b)   Address of Principal Business Office:

                  The following is the address of the principal business office
                  of each of the filing persons:

                  323 Railroad Avenue
                  Greenwich, CT 06830

            (c)   Citizenship:

                  Each of Messrs. Thomas W. Smith, Thomas N. Tryforos and Scott
                  J. Vassalluzo is a United States citizen.

            (d)   Title of Class of Securities:

                  Common Stock, par value $.01 per share.

            (e)   CUSIP Number:

                  784117 10 3

ITEM 3.     If this Statement is filed pursuant to Rules 13d-1(b) or 13d-2(b) or
            (c), check whether the person filing is a:

            Not applicable.

            If this Statement is filed pursuant to Rule 13d-1(c), check this
            box |X|


                                     - 5 -


ITEM 4.     Ownership

            (a)   Thomas W. Smith - 7,703,638 shares; Thomas N. Tryforos -
                  5,762,350 shares; Scott J. Vassalluzo - 5,755,014 shares

            (b)   Thomas W. Smith - 7.3%; Thomas N. Tryforos - 5.5%; Scott J.
                  Vassalluzo - 5.5%

            (c)   Each of Thomas W. Smith, Thomas N. Tryforos and Scott J.
                  Vassalluzo has shared power to vote or to direct the vote and
                  shared power to dispose or to direct the disposition of
                  5,755,014 shares. Thomas W. Smith has the sole power to vote
                  and dispose of 1,948,624 shares, Thomas N. Tryforos has the
                  sole power to vote and dispose of 7,336 shares and Scott J.
                  Vassalluzo has the sole power to vote and dispose of no
                  shares.

ITEM 5.     Ownership of Five Percent or Less of a Class

            Not applicable.

ITEM 6.     Ownership of More than Five Percent on Behalf of Another Person

            Messrs. Smith, Tryforos and Vassalluzo in the aggregate beneficially
            own 6,610,974 shares in their capacities as investment managers for
            certain managed accounts. The managed accounts have the right to
            receive dividends from, and the proceeds from the sale of, the
            managed accounts' shares.

ITEM 7.     Identification and Classification of the Subsidiary Which Acquired
            the Security Being Reported on By the Parent Holding Company

            Not applicable.

ITEM 8.     Identification and Classification of Members of the Group

            Not applicable.

ITEM 9.     Notice of Dissolution of Group

            Not applicable.

ITEM 10.    Certification

            By signing below, I certify that, to the best of my knowledge and
            belief, the securities referred to above were not acquired and are
            not held for the purpose of or with the effect of changing or
            influencing the control of the issuer of the securities and were not
            acquired and are not held in connection with or as a participant in
            any transaction having that purpose or effect.


                                     - 6 -


                                    Signature

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

Date: February 17, 2004

                                                  /s/ Thomas W. Smith
                                           -------------------------------------
                                                    Thomas W. Smith


                                                  /s/ Thomas N. Tryforos
                                           -------------------------------------
                                                    Thomas N. Tryforos


                                                  /s/ Scott J. Vassalluzo
                                           -------------------------------------
                                                    Scott J. Vassalluzo


                                     - 7 -


                             JOINT FILING AGREEMENT

      The undersigned agree that the foregoing Statement on Schedule 13G, dated
February 17, 2004, is being filed with the Securities and Exchange Commission on
behalf of each of the undersigned pursuant to Rule 13d-1(k)

Dated: February 17, 2004

                                                  /s/ Thomas W. Smith
                                           -------------------------------------
                                                    Thomas W. Smith


                                                  /s/ Thomas N. Tryforos
                                           -------------------------------------
                                                    Thomas N. Tryforos


                                                  /s/ Scott J. Vassalluzo
                                           -------------------------------------
                                                    Scott J. Vassalluzo


                                     - 8 -