A 7-year, longitudinal study of children's social development from kindergarten through sixth grade was designed to identify unusually prosocial children and characteristics that differentiated them from average and antisocial peers. Another objective was to identify functional socioemotional predictors of changes in children's social adjustment. Data were collected as part of the evaluation of a school-based intervention program designed to enhance students' prosocial development. Subjects were 303 students, primarily Caucasian and middle-class, from 3 elementary schools. A wide range of variables were assessed, many of them repeatedly, by means of a variety of measures and procedures. As expected, children in prosocial, average, and antisocial groups were found to differ significantly with respect to a large number of measures of social attitudes and values, interpersonal behavior, peer acceptance, school-related attitudes and values, and academic achievement. Curiously, no significant group differences were found for measures of social skill except for perceived social competence. Most differences were found when children were in middle and upper elementary grades. Prosocial children of both sexes, and average girls, improved in adjustment over time, but average boys declined in adjustment. In contrast to the relative stability of antisocial boys, antisocial girls greatly declined in adjustment. (RH)