The present study examined associations between the quality of teacher-child relationships and behavior problems among elementary school students using data from the NICHD Study of Early Child Care and Youth Development, a study of 1,364 children from birth through adolescence. There were two main findings. First, high-quality teacher-child relationships predicted low levels of externalizing behaviors. Second, high-quality relationships acted as protective factors, helping to prevent children with high levels of internalizing behaviors in early childhood from developing trajectories of long-term internalizing behavior problems. Teacher-child relationships may be proximal phenomena that can be targeted in interventions to help prevent behavior problems in middle childhood.