ONE MAJOR PROBLEM IN EDUCATION HAS BEEN TO FIND A METHOD FOR CLASSIFYING STUDENTS THAT WOULD RESULT IN THE GREATEST POSSIBLE GAINS FOR THE STUDENTS AND FACILITATE THE BEST TEACHING TECHNIQUES. EDUCATORS SEEKING ANSWERS TO THIS PROBLEM HAVE EXPERIMENTED WITH DIVIDING CLASSES INTO GROUPS OF A MORE HOMOGENEOUS NATURE, USUALLY ON THE BASIS OF INTELLIGENCE OR ACHIEVEMENT TEST SCORES. ABOUT 30 DIFFERENT EXPERIMENTS IN ABILITY GROUPING WITH AND WITHOUT CONTROL GROUP OF HETEROGENEOUS GROUPING, AT THE ELEMENTARY, JUNIOR HIGH, AND SENIOR HIGH SCHOOL LEVELS FOR STUDENTS OF SLOW, AVERAGE, AND RAPID LEARNING ABILITY ARE REPORTED. IN SOME STUDIES RESEARCHERS TRIED TO KEEP THE METHOD OF INSTRUCTION CONSTANT BY USING THE SAME TEACHERS FOR ALL SECTIONS, BOTH HOMOGENEOUS AND HETEROGENEOUS CLASSES. OTHERS MADE DELIBERATE ATTEMPTS TO ADJUST THE COURSE CONTENT, MATERIALS, AND METHODS TO LEVELS APPROPRIATE FOR EACH SECTION. IT CAN BE CONCLUDED THAT CONTROLLED EXPERIMENTAL STUDIES COMPARING THE EFFECTIVENESS OF HOMOGENEOUS AND HETEROGENEOUS GROUPING, AS EVALUATED BY STUDENT ACHIEVEMENT, SHOWED A GREAT VARIETY OF EXPERIMENTAL DESIGNS AND NO CONSISTENT PATTERN OF RESULTS. MANY EXPERIMENTS FAILED TO CONTROL THE TYPE OF TEACHING AND TO PROVIDE DIFFERENTIATION ACCORDING TO ABILITY LEVELS. OTHERS OVERLOOKED MOTIVATIONAL FACTORS AND ATTEMPTED TO CONTROL ONLY A FEW OF THE POSSIBLE VARIABLES AFFECTING THE LEARNING SITUATION. IN EXPERIMENTS THAT PROVIDED FOR DIFFERENTIATION OF TEACHING METHODS AND MATERIALS, AND ATTEMPTED TO PUSH THE BRIGHT HOMOGENEOUS CLASSES, RESULTS TENDED TO FAVOR THE HOMOGENEOUS OVER THE HETEROGENEOUS GROUPS.