Significance: School-based physical activity interventions require information about children’s typical physical activity patterns throughout the school day. The purpose of this study was to describe the sex-specific patterns of school children’s daily physical activity during activities engaged in before school, during physical education, recess, lunchtime, and after-school as determined using a pedometer. Design: Cross-sectional study of pedometer-determined physical activity during the segmented school day. Eighty-one sixth grade students (28 boys, age= 11.9±0.4 years, BMI=18.8±4.1kg/m2; 53 girls, 11.8±0.5 years, BMI=20.2±4.6kg/m2) wore pedometers (Walk4Life LS2500, Plainfield, IL ) at their waist during waking hours for 4 school days following a brief familiarization period. Research staff were present throughout monitoring days to prompt children to record the number of steps accumulated at distinct time points during the day (e.g., arrival and departure from school, pre- and post-recess, lunchtime, and physical education class). At night children wrote their day-end pedometer values in provided records. Independent t-tests were used to examine sex-specific steps taken during specified segments of the day. The proportions of boys meeting 15,000 steps/day and girls meeting 12,000 steps/day were evaluated as indicative of meeting proposed physical activity guidelines. Results: Boys took significantly more total steps/day than girls: 16421±5444 vs. 12332±3056 steps/day, p<0.001 and more steps during unstructured time (e.g., before school D=1289 steps, recess D=479 steps, lunchtime D=607 steps, and after-school D=1872 steps), but the same number of steps during structured physical education classes (1429±567 vs. 1410±445 steps; p=0.87). Although there was no significant difference in the number of steps taken during recess or physical education for boys (p=0.68), girls took 400 fewer steps at recess compared to physical education (p<0.001). Similar proportions of boys and girls (54.3 vs. 53.6%) met sex-specific physical activity guidelines. These data provide greater understanding of sex-specific activity patterns and the relative contribution of distinct segments of the school day to school children’s total physical activity.