THIS STUDY SOUGHT TO COMPARE THE EDUCATIONAL CHANGES OF EDUCABLE MENTALLY RETARDED CHILDREN ENROLLED IN THE EXPERIMENTAL TWO-TRACK PROGRAM WITH THOSE CHANGES OF MATCHED EDUCABLES ENROLLED IN A ONE-TRACK PLAN. ABOUT 1,800 PUPILS IN CLASSES FOR THE EDUCABLE MENTALLY RETARDED PARTICIPATED IN THIS STUDY. THEY HAD IQ'S RANGING FROM 50-75, WERE FROM 6 TO 18 YEARS OLD, AND WERE DRAWN FROM VARYING ETHNIC, CULTURAL, AND SOCIOECONOMIC LEVELS. PUPILS WERE DIVIDED INTO ONE-TRACK AND INTO TWO-TRACK CLASSES. UNDER THE TWO-TRACK PLAN, EACH PUPIL WAS PLACED EITHER IN A CLASS FOR HIGH ACHIEVERS OR A CLASS FOR LOW ACHIEVERS. UNDER THE SINGLE-TRACK PLAN, HIGH ACHIEVERS AS WELL AS LOW ACHIEVERS WERE PLACED IN THE SAME CLASS AND TAUGHT BY THE SAME TEACHER. IN COMPARING THE EFFECTIVENESS OF THE TWO PLANS, BOTH OBJECTIVE AND SUBJECTIVE DATA WERE USED, AND THE MATCHED PAIR TECHNIQUE WAS EMPLOYED. IN FIFTEEN STUDIES, NO DIFFERENCES IN ACHIEVEMENT WERE FOUND BETWEEN HOMOGENEOUS OR HETEROGENEOUS GROUPING, AND NO HARMFUL EFFECTS FROM HOMOGENEOUS GROUPING. ON THE OTHER HAND, 13 OF THESE STUDIES FOUND DIFFERENCES FAVORING HOMOGENEOUS GROUPING, AND 5 REPORTED RESULTS PARTIALLY FAVORABLE AND PARTIALLY UNFAVORABLE TO HOMOGENEOUS GROUPING. (GC)