The aim of this proposal is to improve our understanding of factors related to brain health and cognition of school-aged children by examining the effects of a 9-month exercise intervention on basic and applied aspects of cognition in preadolescent children. From a basic measurement perspective, event-related brain potentials, MRI, fMRI, and behavioral indices of cognition will be studied during several tasks aimed at assessing various aspects of executive control. Preliminary research has observed faster and more efficient performance in high-fit, relative to low-fit, children and adults using neuroelectric measures that reflect attentional allocation to environmental stimuli and response monitoring processes, along with behavioral measures that reflect response speed and accuracy. These preliminary findings indicate greater top-down attentional control may be associated with increases in physical activity. From an applied measurement perspective, preliminary research has found that children with greater aerobic fitness perform better on standardized achievement tests of reading and mathematics, compared to children with lower aerobic fitness, suggesting that exercise may be related to academic performance in an applied school setting. To date, no causal evidence exists regarding the effects of physical activity on neuroelectric, behavioral, or applied school performance indices of cognition in children. Accordingly, this proposal investigates an aerobic activity training intervention on these measures of cognition using three tasks that require variable amounts of executive control, and on the Illinois Standardized Achievement Test using a randomized control design in which participants are assigned to an afterschool physical activity program or a wait-list control group. Given recent trends identifying decreased levels of physical activity and health status in preadolescents, the understanding of the potential benefits of physical activity on cognition is of great interest. It is imperative that factors positively influencing cognitive function of children be examined to maximize health and effective functioning of individuals as they progress through the lifespan.