ACHIEVEMENT MOTIVATION WAS STUDIED BETWEEN OVER- AND UNDER-ACHIEVING STUDENTS IN THE ELEVENTH-GRADE TO DEVELOP AN OBJECTIVE MEASURE OF MOTIVATION FOR USE IN PREDICTING ACADEMIC SUCCESS OR FAILURE. APPROXIMATELY 800 STUDENTS IN PUBLIC HIGH SCHOOLS WERE SELECTED FOR VALIDATION AND CROSS-VALIDATION SAMPLES. THEY WERE DIVIDED BY SEX AND ACHIEVEMENT. EACH WAS ADMINISTERED TEST ITEMS DESIGNED TO MEASURE INDIVIDUAL DEMOGRAPHY, INCLUDING REFLECTED SELF-CONCEPTS, PERSONALITY TRAITS, AND PREFERENCES FOR CERTAIN TYPES OF OCCUPATIONAL CHARACTERISTICS. ANALYSES OF THE RESULTING DATA WAS PERFORMED TO IDENTIFY THE SUBITEMS WHICH DISCRIMINATED BETWEEN OVER- AND UNDER-ACHIEVING STUDENTS IN EACH SEX AND THOSE WHICH DID NOT DISCRIMINATE (VALID ITEMS). COMMON SUBITEMS RELATING TO EDUCATIONAL-OCCUPATIONAL STATUS AND MOTIVATION, APTITUDE, AND GRADE POINT AVERAGE WERE MUCH MORE PREVALENT FOR THE OVER-ACHIEVING SAMPLE, UNDOUBTEDLY DUE TO THE HIGH DROPOUT RATE OF THE UNDER-ACHIEVING SAMPLE BETWEEN TENTH AND ELEVENTH GRADES. ABOUT 75 PERCENT OF THE SUBITEMS WERE VALID FOR BOTH SEXES, BUT VALIDITY PROVED MORE FOR MALES THAN FEMALES. THIS INFORMATION PROVIDED THE GROUNDWORK FOR A RESEARCH INSTRUMENT WHICH, WHEN DEVELOPED, COULD ADD UNDERSTANDING TO THE MOTIVATIONAL COMPLEX. (JH)