This study investigates the extent to which teacher-student interactions in fifth grade classrooms are associated with peer behavior in fifth grade, accounting for prior peer functioning. Participants included 894 fifth grade students from the NICHD Study of Early Child Care and Youth Development. The quality of teacher-student interactions (emotional support, classroom organization, and instructional support) was assessed through classroom observations in fifth grade; peer behavior was assessed via teacher report (prosocial behavior, aggression, relational aggression, and asocial behavior) in fourth and fifth grades and classroom observations (sociable/cooperative peer behavior) in third and fifth grades. Multiple regression analyses revealed that children in fifth grade classrooms with higher quality organization interactions had more positive observed interactions with their peers and lower teacher ratings of aggression and relational aggression. In addition, emotional support interactions were related to higher teacher ratings of prosocial behavior. Implications and limitations of the findings are discussed. (Contains 3 tables and 1 figure.)