This study examined the joint effects of the quality of teacher-student relationship support (TSRS) and normative levels of classroom aggression on individual aggression in a sample of 687 second-grade children who entered first grade with relatively low reading readiness skills. Using a prospective design, the present study explored the joint effects of teacher-rated TSRS and normative classroom aggression on both teacher- and peer-rated aggression, controlling for levels of baseline aggression. The study also examined the effect of peer-rated TSRS on teacher- and peer-rated aggression. Furthermore, ethnic and sex differences on study variables and on their relationships were examined. Boys were rated by teachers and peers as having higher aggression levels and lower Time 1 and Time 2 TSRS than girls. African American students were rated by teachers and peers as having higher Time 1 and Time 2 aggression levels. African American students were rated by teachers as having lower Time 1 and Time 2 TSRS than Hispanic and White students. Hispanic students had higher peer-rated TSRS than African American students at Time 1. Furthermore, African American and Hispanic students were more likely to be placed in higher aggressive classrooms than were White students. Regression analyses found that, after controlling for baseline aggression, teacher-rated TSRS predicted peer- and teacher-rated aggression. However, neither normative classroom aggression nor the interaction of normative classroom aggression with teacher-rated or peer-rated TSRS predicted teacher-rated aggression. Peer-rated TSRS did not predict teacher-rated or peer-rated aggression. There was no evidence ethnicity moderated the relationships between TSRS and aggression. Study limitations and implications for intervention are also discussed.