We used a longitudinal data set to evaluate an observational assessment of adolescent competence within a group context. Participants were 40 (21 males, 19 females) ethnically diverse children who had earlier been observed in summer camp (age 10) and preschool (age 41/2), as well as in infancy. A revealed differences task was videotaped as part of an intensive weekend camp reunion at ages 15 to 16. Raters, blind to the adolescents' developmental histories, coded each adolescent on the following behavioral rating scales: enjoyment of the task, involvement, leadership, self-confidence in the task, and global social competence. Both concurrent validity (strong correlations with independent camp reunion counselor ratings and peer sociometric measures) and clear associations with antecedent measures of peer competence in preschool and middle childhood were demonstrated. A pattern of correlations revealed considerable discriminate validity. Neither IQ nor socioeconomic status accounted for these associations. Overall, the results confirm the power of a developmentally appropriate, taxing, behaviorally based assessment of group functioning as a measure of competence in adolescence.