We examined the effects of a 7-month jumping intervention (10 minutes, 3 times per week) on bone mineral gain in prepubertal Asian and white boys (10.3 ؎ 0.6 years, 36.0 ؎ 9.2 kg) at 14 schools randomized to control (n ؍ 60) and intervention (n ؍ 61) groups. Intervention and control groups had similar mean baseline and change in height, weight, lean mass and fat mass, baseline areal bone mineral density (aBMD; g/cm 2 ), bone mineral content (BMC; g; dual-energy X-ray absorptiometry [DXA], QDR 4500W), and similar average physical activity and calcium intakes. Over 7 months, the intervention group gained more total body (TB) BMC (1.6%, p < 0.01) and proximal femur (PF) aBMD (1%, p < 0.05) than the control group after adjusting for age, baseline weight, change in height, and loaded physical activity. We also investigated the 41 Asian and 50 white boys (