This study explored the link between classroom-level problem behaviors and teacher-child interaction quality in 307 Head Start preschool classrooms. The moderating role of the classroom’s age composition (e.g., 3- and 4-year-olds versus 4-year-olds only) also was examined. Using a dataset of 852 3-year-old children and 1114 4-year-old children, classroom-level problem behaviors were operationalized using teacher reports of children’s problem behaviors. (author abstract)