<TABLE> <S> <C>

<PAGE>
 
<ARTICLE> 6
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM THE
STATEMENT OF ASSETS AND LIABILITIES, THE STATEMENT OF OPERATIONS, THE STATEMENT
OF CHANGES IN NET ASSETS AND THE PER UNIT DATA AND RATIOS CONTAINED IN THE
FINANCIAL STATEMENTS OF THE FUND TO WHICH THIS SCHEDULE RELATES AND IS QUALIFIED
IN ITS ENTIRETY BY REFERENCE TO SUCH FINANCIAL STATEMENTS.
</LEGEND>
<CIK> 0000878375
<NAME> ABA MEMBERS/STATE STREET COLLECTIVE TRUST
<SERIES>
   <NUMBER> 0
   <NAME> STRUCTURED PORTFOLIO SERVICE-CONSERVATIVE FUND
       
<S>                             <C>
<PERIOD-TYPE>                   9-MOS
<FISCAL-YEAR-END>                          DEC-31-1998
<PERIOD-START>                             JAN-01-1998
<PERIOD-END>                               SEP-30-1998
<INVESTMENTS-AT-COST>                       20,475,501
<INVESTMENTS-AT-VALUE>                      21,505,575 
<RECEIVABLES>                                  225,361
<ASSETS-OTHER>                                       0
<OTHER-ITEMS-ASSETS>                                 0
<TOTAL-ASSETS>                              21,730,938
<PAYABLE-FOR-SECURITIES>                       225,381 
<SENIOR-LONG-TERM-DEBT>                              0
<OTHER-ITEMS-LIABILITIES>                            0
<TOTAL-LIABILITIES>                            226,606
<SENIOR-EQUITY>                                      0
<PAID-IN-CAPITAL-COMMON>                             0
<SHARES-COMMON-STOCK>                                0 
<SHARES-COMMON-PRIOR>                                0
<ACCUMULATED-NII-CURRENT>                            0
<OVERDISTRIBUTION-NII>                               0
<ACCUMULATED-NET-GAINS>                              0
<OVERDISTRIBUTION-GAINS>                             0
<ACCUM-APPREC-OR-DEPREC>                             0
<NET-ASSETS>                                21,504,130
<DIVIDEND-INCOME>                                    0   
<INTEREST-INCOME>                                    0
<OTHER-INCOME>                                       0
<EXPENSES-NET>                                  12,771
<NET-INVESTMENT-INCOME>                       (12,771)
<REALIZED-GAINS-CURRENT>                     1,893,931
<APPREC-INCREASE-CURRENT>                    (644,704)
<NET-CHANGE-FROM-OPS>                        1,038,456  
<EQUALIZATION>                                       0
<DISTRIBUTIONS-OF-INCOME>                            0
<DISTRIBUTIONS-OF-GAINS>                             0
<DISTRIBUTIONS-OTHER>                                0
<NUMBER-OF-SHARES-SOLD>                        741,410
<NUMBER-OF-SHARES-REDEEMED>                  (495,864)
<SHARES-REINVESTED>                                  0
<NET-CHANGE-IN-ASSETS>                       4,276,312
<ACCUMULATED-NII-PRIOR>                              0
<ACCUMULATED-GAINS-PRIOR>                            0
<OVERDISTRIB-NII-PRIOR>                              0
<OVERDIST-NET-GAINS-PRIOR>                           0
<GROSS-ADVISORY-FEES>                                0
<INTEREST-EXPENSE>                                   0
<GROSS-EXPENSE>                                      0
<AVERAGE-NET-ASSETS>                        20,623,453
<PER-SHARE-NAV-BEGIN>                            12.97
<PER-SHARE-NII>                                 (0.01)
<PER-SHARE-GAIN-APPREC>                          0.70
<PER-SHARE-DIVIDEND>                             0.00
<PER-SHARE-DISTRIBUTIONS>                        0.00
<RETURNS-OF-CAPITAL>                                0
<PER-SHARE-NAV-END>                             13.66
<EXPENSE-RATIO>                                  0.08
<AVG-DEBT-OUTSTANDING>                              0
<AVG-DEBT-PER-SHARE>                                0
        


</TABLE>