Recent reviews of the literature have demonstrated that exercise seems to have a positive impact on cognitive performance in both adults and children. One of the mechanisms that has been proposed for this relationship is that exercise increases cognitive inhibition. Cognitive inhibition is the suppression and/or clearing of irrelevant information or stimuli from consciousness, which allows the brain to process information more efficiently. The purpose of this research study was to assess the impact of an acute bout of exercise on inhibition and cognitive performance. Two studies were performed, the first examining the effects of physical education class on inhibition in a sample of third graders, the second examining the effects of an acute bout of aerobic exercise on arousal and inhibition in college-age adults. In Study 1, the effects of 15 minutes of physical education were compared to 15 minutes of regular classroom activities. In Study 2, the effects of 20 minutes of self-paced moderate-intensity running on a treadmill were compared to the effects of a 20-minute sedentary control period. In both studies, cognitive inhibition was assessed using Stroop interference and negative priming tests, and cognitive performance was assessed using digit-symbol substitution tasks. Physical activity levels during the experimental conditions were measured using CSA 7164 activity monitors. Also, in Study 2 arousal was measured using heart rate monitors and the Activation-Deactivation Adjective Checklist. Results from Study 1 showed that the physical education class did not have a significant impact on inhibition or cognitive performance. This lack of significant findings may be due to the methodological constraints of working in a school environment and/or developmental issues that may limit the impact of exercise on the cognitive measures used in this study. In Study 2, a positive impact of exercise on inhibition was found. Specifically, participants showed improved performance on the Stroop interference task (ES=0.26) with no concomitant improvement on the negative priming task. This finding suggests that exercise may lead to increases in inhibition, thus increasing the efficiency with which the brain can process information. Implications of these findings, as well as methodological issues relating to performing research in a school environment, will be discussed.Keyword(s): exercise/fitness, performance, physical activity