Existing literature shows promising effects of physical activity on children's cognitive outcomes. This study assessed via a randomized, controlled design whether additional curricular physical activity during the school day resulted in gains for children's fluid intelligence and standardized achievement outcomes. Participants were children (N?=?460) from four urban schools in the Southeast United States. Schools were randomly assigned to treatment and control conditions. Treatment schools received additional physical activity breaks throughout the school day while control schools maintained a typical schedule without curricular activity breaks. Results from the one-year study show positive effects for children's mathematics and reading achievement but no differences across treatment and control groups for children's fluid intelligence scores. Implications for school psychologists in promoting physical activity breaks on a systems-wide level are discussed.