The present longitudinal research demonstrates robust contributions of earl
y prosocial behavior to children's developmental trajectories in academic a
nd social domains. Both prosocial and aggressive behaviors in early childho
od were tested as predictors of academic achievement and peer relations in
adolescence 5 years later: Prosocialness included cooperating, helping, sha
ring, and consoling, and the measure of antisocial aspects included pronene
ss to verbal and physical aggression. Prosocialness had a strong positive i
mpact on later academic achievement and social preferences, but early aggre
ssion had no significant effect on either outcome. The conceptual model acc
ounted for 35% of variance in later academic achievement, ann 37% of varian
ce ill social preferences. Additional analysis revealed that early academic
achievement did not contribute to later academic achievement after control
ling for effects of early prosocialness. Possible mediating processes by wh
ich prosocialness may affect academic achievement and other socially desira
ble developmental outcomes are proposed.