A study was conducted to examine social behavior by one-year-old boys over the course of a three-month playgroup experience. The "clusters" chosen for examination consisted of temporary groups (often less than a minute) the toddlers formed to focus on a single activity. Socially directed behavior is defined here as vocalizing, laughing and manipulating a toy while looking at another child. The five Ss ranged in age from 13 to 15 months at the first session. The playgroup met for about 2 1/2 hours each Monday and Friday in a room containing a variety of toys and play equipment, with parental supervision. The playgroup was videotaped for one hour each Friday morning. Behavior was analyzed by locating all clusters on the videotapes, coding their duration, participation, and then searching each cluster for measures of social intent. Results showed that: (1) clusters did not vary significantly across months in frequency, duration or number of children participating; (2) type of play activity did not relate to month or cluster duration; (3) despite a significant increase in clusters forming about inactive children, those forming around active children remained in the majority in month 3; (4) vocalizations and toy manipulations did not increase as expected; they were frequent even during the first month; and (5) the extent and complexity of social behavior increased during the three-month period. (KM)