THE MAJOR HYPOTHESIS OF THIS PROJECT WAS THAT TRAINABLE MENTALLY RETARDED CHILDREN ATTENDING SCHOOL PROGRAMS, WHETHER LIVING AT HOME OR IN AN INSTITUTION, WOULD SHOW GREATER INCREMENTS OF SOCIAL COMPETENCE OVER A PERIOD OF TIME THAN COMPARABLE CHILDREN NOT ATTENDING SUCH PROGRAMS. IT WAS ALSO SUGGESTED THAT PARENTS OF RETARDATES WHO ATTEND PUBLIC SCHOOL CLASSES IN THEIR COMMUNITIES WOULD SHOW GREATER INCREMENTS OF ADAPTABILITY THAN THOSE WHOSE CHILDREN DO NOT ATTEND SUCH CLASSES. FROM ABOUT 180 CHILDREN, 4 GROUPS WERE FORMED--(1) COMMUNITY CONTROL, (2) COMMUNITY EXPERIMENTAL, (3) INSTITUTIONAL CONTROL, AND (4) INSTITUTIONAL EXPERIMENTAL. THE EXPERIMENTAL GROUPS ATTENDED PUBLIC SCHOOL CLASSES FOR TRAINABLE CHILDREN WHILE THE CONTROL GROUPS DID NOT. RATINGS ON THE CRITERION MEASURES WERE OBTAINED AT THE INITIATION AND CONCLUSION OF THE 2-YEAR EXPERIMENTAL PERIOD. PARENTS OF THE COMMUNITY GROUPS WERE VISITED AND INTERVIEWED FOUR TIMES DURING THE PROJECT PERIOD. ANALYSIS OF FINDINGS SHOWED SIGNIFICANT INCREASES IN THE SOCIAL COMPETENCY DEVELOPMENT FOR THE COMMUNITY GROUPS AND COMPARABLE DECREASES FOR THE SAME IN THE INSTITUTIONAL GROUPS. DEVELOPMENTAL DIFFERENCES BETWEEN THE SCHOOL AND NONSCHOOL CHILDREN, WHETHER LIVING AT HOME OR NOT, WERE INSIGNIFICANT. IT WAS THEREFORE CONCLUDED THAT SCHOOL PROGRAMS FOR TRAINABLE MENTAL RETARDATES WERE INADEQUATE IN FOSTERING SOCIAL COMPETENCY DEVELOPMENT. ALSO, THE ENVIRONMENT OF A HOME APPEARED TO BE MUCH MORE STIMULATING FOR THIS SOCIAL DEVELOPMENT THAN THE INSTITUTIONAL ENVIRONMENT. PARENTAL ADAPTABILITY APPEARED NOT TO BENEFIT WHEN CHILDREN ATTENDED SCHOOL, POSSIBLY BECAUSE OF LACK OF PARENT-TEACHER CONTACTS AS WELL AS INADEQUACY OF THE FEW CONTACTS THAT OCCURRED. (JH)