BACKGROUND The benefits of childhood physical activity include fitness, weight control, and exercise habits that may carry over into adulthood. School physical education is the primary program responsible for training the nation's youth to be physically active and national objectives call for students to be engaged in moderate-to-vigorous physical activity at least 50% of class time. The purpose of this study was to determine through systematic observation in a regional sample of elementary and middle schools the amount of moderate-to-vigorous physical activity students obtain during physical education classes. METHODS Twenty elementary schools and 7 middle schools were randomly sampled from the 355 elementary schools and 117 middle schools in the 20 school districts in Harris County, Texas. In addition, 9 elementary and 6 middle schools that were identified as having excellent physical education programs were sampled purposively to provide a comparison. Seven systematic observations of student's physical activity were conducted during physical education in each school. RESULTS The average moderate-to-vigorous physical activity in the randomly selected elementary schools was 8.6%, significantly less (P < 0.05) than for the randomly selected middle schools (16.1%) or for the comparison elementary schools (20.6%) and middle schools (24.0%). CONCLUSIONS The average amount of physical activity observed in this regional sample of schools was less than the estimated national average of 27% and far less than the national recommendation calling for a minimum of 50%.