This article describes a school-based study designed to promote social competence and reduce aggressive behavior by strengthening children's skills in processing social information and regulating emotions. Three successive cohorts of 3rd graders (N = 548) from 2 schools participated. In 2000-2001, children received a routine health curriculum; in 2001-2002, students received the Making Choices: Social Problem Solving Skills for Children (MC) program; and in 2002-2003, children received MC supplemented with teacher and parent activities. Compared with children in the routine condition, children in both MC conditions were rated lower on posttest social and overt aggression and higher on social competence. Moreover, they scored significantly higher on an information-processing skills posttest. The findings suggest that prevention programs can strengthen social-emotional skills and produce changes in aggressive behavior.