School attachment is a robust predictor of adjustment in children and youth. Previous research has demonstrated effects of school context on student attachment, but individual-level contributions have not been explored. Our study examined the role of affiliative orientation in school attachment and aggressive behavior in children and youth from Grades 3 through 12. A total of 834 students in three school districts completed self-report measures of affiliative motivation, attachment to school, and frequency of physically and relationally aggressive acts. Results supported the hypothesis that students high in affiliative orientation reported higher levels of school attachment and lower levels of physical and relational aggression. Path analysis indicated that the relation of affiliative orientation to aggression was mediated by school attachment, but that the mediational effect was moderated by sex. Male students, and students of both sexes with low affiliative motivation, may receive special benefit from practices designed to increase school attachment. © 2006 Wiley Periodicals, Inc. Psychol Schs 43: 231–246, 2006.