Attention-Deficit/Hyperactivity Disorder (ADHD) affects an estimated 2 million children in the United States, making it one of the most common mental disorders among children today (West, 1999). Characterized by inattention, hyperactivity, and impulsivity, children diagnosed with ADHD often struggle academically and socially. The purpose of this study was to examine the effects of physical education class on the behavior of children diagnosed with Attention-Deficit/Hyperactivity Disorder (ADHD). Fourteen male and six female students in grades three through five were observed by their classroom teacher. Of the twenty students, ten were diagnosed with ADHD and ten were not. Classroom teachers rated their students' behavior using the Iowa Connors Teacher's Rating Scale at two different times during the day for nineteen days (Pelham, W. E., Milich, R., & Murphy, D. A., 1989). A higher score indicated greater inattention, hyperactivity, and impulsivity while a score of zero indicated "good" behavior. On seven of the nineteen days, students participated in an organized physical education class between the two observation times. It was hypothesized that students diagnosed with ADHD would receive lower scores on the rating scale during the hour following physical education classes compared to scores during the hour prior to physical education class. It was also hypothesized that the results would reveal a reduction in teacher rating scores following physical education (PE) and this effect would be larger for youth with ADHD than for youth without ADHD. Results from a time x ADHD x PE repeated measures analysis of variance (ANOVA), conducted to determine the effects of physical activity on rating scale scores, supported this hypothesis. Furthermore, a marginally significant interaction was found between time, PE, and ADHD using one-tailed repeated measures t-tests. In the nonPE condition, rating scores increased significantly from pre to post for students with ADHD. Under the PE condition, scores of the non-ADHD children increased from pre to post while scores of children with ADHD decreased from pre to post. Overall, involvement in PE class had a positive effect on the behavior of children with ADHD. Not only did their behavior improve after participation in physical education, but their behavior deteriorated significantly on days without physical education. Involvement in PE class had no effect on children without ADHD.Keyword(s): elementary education, physical activity, research