Objective: To determine the effect of a twice-weekly, school-based, 10 minute jumping regime on muscle and fat tissue in healthy adolescent boys and girls. Methods: We replaced regular warm up activities with jumping in physical education (PE) classes of early high school students for 8 months to observe the effect on muscle and fat tissue. A total of 99 adolescents (46M, 53F; 13.8 ᠰ.4 years) volunteered to participate. Intervention group subjects performed ten minutes of varied jumping activity, while control subjects performed a regular PE warm-up. Biometrics, Tanner staging, age of peak height velocity (PHV), vertical jump, whole body lean tissue, and fat mass (DXA-derived) were measured at baseline and follow-up. Physical activity was determined by questionnaire. Results: There were no differences in any measured variable between control and intervention groups at baseline. Boys had a significantly older age of PHV than girls (p = 0.02). No group differences were detected for 8-month change in height, weight or maturity measures for the combined sample; however at 8-months jumpers had accrued greater lean tissue mass than controls (p = 0.002). Sex-specific analysis revealed that intervention group boys had gained more lean tissue mass than controls (p = 0.016) and experienced significant fat loss (p = 0.010) than controls, an effect that was not observed in the girls. Conclusion: Regular, short duration, jumping activity during adolescence increased lean tissue mass and boys additionally lost fat mass. Sex-specific and/or maturation-specific factors may explain the disparity in effect.