THE CONCEPTUAL AND EMPIRICAL STATUS OF ACHIEVEMENT MOTIVATION WAS EVALUATED WITH RESPECT TO ESTABLISHING AN OBJECTIVE, QUANTIFIED, PREDICTIVE MEASURE OF SCHOOL PERFORMANCE FOR MENTALLY RETARDED CHILDREN. COMPARATIVE ANALYSES WERE MADE AMONG 3 SUBJECT SAMPLES--(1) A CONTROL GROUP OF 60 NORMAL CHILDREN, (2) AN EXPERIMENTAL GROUP OF 42 MENTAL RETARDATES, NOT IN SPECIAL CLASSES, AND (3) A SECOND EXPERIMENTAL GROUP OF 47 RETARDATES ENROLLED IN SPECIAL CLASSES. THE MEAN AGES OF THE GROUPS RANGED BETWEEN 15 AND 16 YEARS. MEASURES OF ACHIEVEMENT MOTIVATION, DERIVED FROM PROJECTIVE MEASUREMENTS IN INDIVIDUAL INTERVIEWS, AND MEASURES OF INTELLIGENCE AND ACADEMIC PERFORMANCE WERE OBTAINED AND ANALYZED. FINDINGS SHOWED THAT ACHIEVEMENT MOTIVATIONAL MEASURES WERE NOT READILY APPLICABLE TO THE PREDICTION OF ACADEMIC PERFORMANCE, EVEN WHEN CORRELATED WITH AN INTELLIGENCE MEASURE. RECOMMENDATIONS CALL FOR FUTHER RESEARCH ON THE FACTORS OF STUDENT BEHAVIOR, CHILD-REARING PRACTICES, AND STUDENT PERSONALITY RELATIONSHIPS AS EACH MIGHT RELATE TO SCHOOL ACHIEVEMENT. (JH)