We examined similarities among 45 sibling pairs in Grades 2 to 5 in their social and academic adaptation to the school setting. Measures included teacher ratings and rankings of academic skills, social behavior, and peer acceptance; peer sociometric ratings; and direct observations on the playground with peers and in the classroom with teachers and peers. Comparisons were made with randomly selected, unrelated subject pairs matched on sex, grade, and classroom. Significant correlations were found only among sibling pairs on peer ratings of social preference, teachers' judgments of academic competence, popularity, social behavior and school adjustment, positive behavior with peers on the playground, and teachers' disapproving behavior in the classroom. The results underscore the need for more multiagent and multimethod research on sibling concordant–discordant adjustment regardless of theoretical orientation.