This study investigated the impacts of "INSIGHTS into Children's Temperament" on instructional support and math and reading skills in kindergarten and first grade classrooms with high levels of student shyness. "INSIGHTS" is a temperament-based intervention with teacher, parent, and classroom programs. 22 urban elementary schools (randomly assigned to "INSIGHTS" vs. comparison group), 90 teachers, and 435 children enrolled in the study. Multi-level modeling demonstrated larger impacts of "INSIGHTS" on instructional support in first grade classrooms with high levels of student shyness. Analyses also showed larger impacts of "INSIGHTS" on math skills for students in classrooms with high levels of shyness. Results suggest the importance of considering temperament at the classroom-level when implementing temperament-based intervention.