This study examined how children's aggression and prosocial behavior are related to the preference and popularity of their best friends. Participants were 1,953 fourth-graders (52.2% boys). Measures included peer nominations of friendship, peer status, overt and relational aggression, and prosocial behavior. A total of 334 reciprocal same-sex best friend dyads were identified. The Actor-Partner Interdependence Model (Kashy & Kenny, 1999) showed that best friends' peer status significantly predicted children's behavior. For boys, best friends' preference was negatively associated with overt aggression, while best friends' popularity was positively associated with overt aggression. For girls, best friends' popularity was positively related to both relational aggression and prosocial behavior. The model also revealed high similarity between friends in both preference and popularity. This study highlighted the distinction between two dimensions of peer status in the study of friendship and peer influence in middle childhood. It also demonstrated how individual, dyad, and group characteristics can be integrated in the study of children's social relationships. (Contains 2 tables and 1 figure.)