This study investigated the efficacy of the INSIGHTS into Children's Temperament intervention in supporting the academic development of shy kindergarten and first-grade children. INSIGHTS is a temperament-based intervention with teacher, parent, and classroom programs. The participants included 345 children from 22 low-income, urban elementary schools who were randomly assigned to INSIGHTS or a supplemental after-school reading program. Growth-curve modeling showed that shy children in INSIGHTS evidenced more rapid growth in critical thinking and math than their shy peers in the attention-control condition during kindergarten and the transition to first grade. The effects of INSIGHTS were partly indirect through improved behavioral engagement. INSIGHTS enhances the academic development of early elementary school children with shy temperaments.