Preadolescent children, when compared to young adults, exhibit lower cognitive performance on laboratory tasks, presumably due to the underdeveloped or immature brain structures that subserve various cognition functions. Similar findings have been observed in older adults due to decrements in the central nervous system that accompany the aging process (Kramer, Hahn, & Gopher, 1999). However, research examining physical activity participation in older adults has found that exercise ameliorates, in part, the lower cognitive performance observed in older adults, suggesting a beneficial relationship between physical activity and cognitive health (Hillman et al., 2002; 2003; 2004; Kramer et al., 1999). To date, this relationship has not been examined in preadolescent children. Thus, the relationship between age, physical fitness, and neuroelectric and behavioral indices of cognitive function was investigated by comparing higher and lower physically fit preadolescent children and young adults. Physical fitness was assessed using the Fitnessgram test and cognitive function was measured by neuroelectric and behavioral responses to a stimulus discrimination task. Specifically, the P3 component of the event-related brain potential (ERP), reaction time (RT), and response accuracy were recorded during a visual oddball task from 28 fit and sedentary children (M=9.5 years) and 34 fit and sedentary adults (M=19.5 years) such that approximately an equal number of participants were placed in each of the four groups. The oddball task requires participants to discriminate between two stimuli that differ in occurrence probability. Results indicated that increased physical fitness was beneficial to neuroelectic function associated with attentional and working memory processes in preadolescent children. That is, P3 amplitude was greater for children compared to adults, and for fit compared to sedentary participants. Further, age interacted with fitness such that larger P3 amplitude was observed for fit children compared to the other three groups. Fitness also benefited neurocognitive indices of stimulus evaluation speed (P3 latency) across age groups, and this effect was qualified by task condition such that improved speed was only observed for the more demanding condition. Fitness effects were also observed in performance behavior with improved response speed and accuracy for higher, compared to lower, fit preadolescent children. These findings suggest that physical fitness is related to improved cognitive functioning in preadolescent children.Keyword(s): elementary education, exercise/fitness, research