Some individuals with developmental disabilities and emotional disorders may engage in challenging behavior that can result in the use of aversive procedures and/or seclusion from typically developing peers. They may also engage in low levels of physical activity. One way to decrease challenging behaviors while increasing overall levels of physical health may be to provide access to exercise systematically throughout the day. This study used a multiple-baseline across-participants design to investigate the effects of antecedent exercise on the challenging behavior of three boys with moderate to severe developmental disabilities and an emotional behavior disorder. Each participant engaged in eight daily exercise sessions ranging in duration from 1 to 20 min throughout the entire school day across school settings. Challenging behavior decreased to zero for two participants and near zero for the third participant. (Contains 4 tables and 1 figure.)