The purpose of this study was to examine the effects of directed fitness activities and free-play time on sixth grade students in relation to their self-concept, academic grade average, and classroom conduct. Also measured was the effect on aerobic fitness, body composition, body esteem, and attitude towards physical activity. A total of 229 boys and girls received treatment for 30 minutes, 4 days a week for 12 weeks. The subjects were rated as "high-level" or "low-level" students by their fifth grade teachers, based on previous classroom performance. Approximately half of each group received vigorous aerobic exercise during treatments, while the others were allowed free-play time and served as controls. Significant differences were found between groups for their change in total self-concept. Test subjects improved 2.5% and controls fell 3.1%. The greatest changes were in the scores of the high-level students. The same pattern was found in the measurement of body-esteem. Significant correlations were found between self-concept and body-esteem. In the areas of academic performance and conduct there were significant differences in how the groups changed. Test subjects improved 1.2% in academic grades, while controls decreased by 0.2%. Both groups received lower conduct scores, but the control subjects fell by a greater margin than the test subjects. The greatest change in the two classroom measurements came from the low-level students, with the high-level students contributing very little to the group differences. There were no significant differences between the two groups in height gained, but for measurements of weight, skinfold thickness, and body mass, significant differences did develop during the project, with test subjects decreasing in each variable and controls slightly increasing. Activity level was measured by Caltrac accelerometers. Test subjects were found to be nearly twice as active during treatment sessions when compared to the control subjects. On the post-test 12-minute run, the test subjects improved by a statistically significant margin, the control subjects did not. It was concluded that self-concept, academic grades and classroom conduct can be enhanced as a result of aerobic exercise.Keyword(s): curriculum development, middle school issues, physical activity