Theoretical models of job stress suggest that teachers' experience with burnout occurs, in part, because of an imbalance between job demands and the resources available to meet those demands. Using a diverse sample of 230 Head Start educators, the present study explored how school-based demands (i.e., class size, behavioral challenges) and resources (i.e., school social supports) contributed to teachers' self-reported burnout. Findings revealed that greater social support, specifically leads teachers' relationship with their assistant teacher (TA), was associated with lower ratings of burnout. There was also a significant interaction between classroom behavior problems and TA relationship quality, such that relationship quality reduced burnout in classrooms with low and average levels of behavior problems, but not in classrooms with high levels of behavior problems. Implications of these findings for preschool teacher well-being are discussed.