THE INTELLECTUAL DEVELOPMENT, ACADEMIC ACHIEVEMENT, AND SOCIAL AND PERSONAL ADJUSTMENT OF EDUCABLE MENTALLY RETARDED CHILDREN ENROLLED IN SPECIAL CLASSES WERE COMPARED TO THOSE OF PEERS IN REGULAR GRADES. ABOUT 125 CHILDREN, BEGINNING FIRST GRADE AND HAVING A MEAN IQ OF 75 (STANFORD-BINET SCALE), WERE DIVIDED RANDOMLY INTO AN EXPERIMENTAL GROUP AND A CONTROL GROUP. A SERIES OF INTELLECTUAL, ACADEMIC, AND PERSONAL ADJUSTMENT MEASURES WAS ADMINISTED TO ALL THE CHILDREN ANNUALLY FOR 4 YEARS. DURING THIS PERIOD AN ATTRITION OF ABOUT THREE-FOURTHS OF THE ORIGINAL SAMPLE TOOK PLACE. THIS, HOWEVER, DID NOT SIGNIFICANTLY AFFECT THE STUDY RESULTS. THERE WERE NO STATISTICALLY SIGNIFICANT DIFFERENCES IN IQ GAINS BETWEEN THE SPECIAL CLASSES GROUP AND THE REGULAR GRADES GROUP, AND SEVERAL SOCIAL FACTORS WERE FOUND TO BE RELATED TO INCREASES IN IQ. THE ANALYSIS OF ACADEMIC ACHIEVEMENT INDICATED THAT THE SPECIAL CLASS IS BENEFICIAL TO CHILDREN WHOSE IQ'S ARE 80 AND BELOW, BUT THAT IT IS NOT NECESSARILY AN EFFECTIVE EDUCATIONAL SETTING FOR SIGNIFICANTLY IMPROVING ACADEMIC ACHIEVEMENT OF CHILDREN USUALLY CLASSIFIED AS BORDERLINE OR SLOW LEARNERS, WHO HAVE IQ'S ABOVE 80. FINDINGS ON PERSONAL ADJUSTMENT SHOWED THAT SPECIAL CLASSES ENCOURAGED THE RETARDATES TO DISPLAY ORIGINALITY AND FLEXIBILITY IN THEIR THINKING. (JH)