Obesity continues to be a major health problem for children. Attempts by physical educators to reverse this trend have been only marginally successful. Traditional formats used for class scheduling may not allow for the duration of exercise necessary for significant, healthy body composition changes. In addition to instruction, which is critical to the education process, necessities such as dressing, showering, and administrative activities consume significant amounts of time. The purpose of the study was to examine body fat changes of children enrolled in a five-week summer course, which allowed for a longer period of continuous activity. Tenth grade students, ages 15-16 years, met five days a week for four hours per day. All students (n=28) enrolled in the class volunteered for the study. The daily program included participation in four different activities for one hour each. This course differed from the regular curriculum only in duration of class activity. Results showed a mean fat loss for all students of 1.3% (t=5.20, p<0.05). Students measuring in the higher 50% fat on the pretest lost significantly more fat (1.7%) than those in the lower 50% (t=4.28, p<0.05). These results suggest that the public school physical education curriculum can be effective in reducing % fat in children when the physical activity is of appropriate duration. The benefits appear to be greater for those in greatest need. The findings also support the new curriculum models such as block scheduling which extends the duration of school classes.