Mentally retarded children were studied for their conceptual development and movement from the ability to perceive persons as separate entities but not in significant interaction (aprasia) to group activity. A quasi-projection technique was used to test six groups of 20 boys each, including institutionalized and family-based normals (aged 6 and 12) and retardates (aged 12, with IQ's to 65 and mental ages 6 to 7). Each child analyzed one group and then synthesized another in the settings of home, play, work, and school to solve a problem. Evaluation considered whether the following group characteristics were present and how abstract they were: the identifiable unit, social structure, role behavior, reciprocal relations, normative behavior, common interests, common goals, and continuity. Results indicated a greater incidence and degree of aprasia among retardates than normals of the same chronological age, and a greater degree among the institutionalized than those in a family setting in comparable groups (p=.001 for both); little or no difference between retardates and normals of the same mental age; more difficulty in synthesizing than in analyzing a similar situation (p=.02 to .001); and poorer scoring on comprehension of role, normative behavior, and group identification. (Author/SN)