This study tested the predictive links between children's interactions with peers in early elementary school and their social and emotional adjustment at the end of elementary school. A sample of 231 boys starting kindergarten and first grade were observed during this longitudinal study, on three separate occasions: kindergarten and first grade, first and second grade, and finally, fifth and sixth grade, respectively. Data were collected using peer-, teacher-, and self-report methodologies at each time. Play group observational data were also recorded in observations 1 and 2. Composite measures of four central social behaviors (aggression, disruptive behavior, withdrawal, and prosocial behavior) were computed for each observation. The results demonstrated that aspects of early peer interaction are important predictors of later social adjustment outcomes, and highlighted the importance of starting intervention efforts in the early elementary school years. In particular, boys who had been consistently rejected demonstrated several social adjustment problems after the 5-year interval. (AA)