This study was designed to analyze the significance of the recess period and "the effect of its duration" on children's daily physical activity. Thirteen pupils attending school in a rural area were monitored with accelerometers during the study weeks. The intervention consisted of modifying regularly scheduled recess period for a month. Data from two school days during the third week were recorded for analyses. Analyses indicated that, according to the recommended 2 x 15 min recess schedule, children spent on average from 16.9 [plus or minus] 5.7 min to 22.8 [plus or minus] 3.7 min each day in moderate-to-vigorous physical activity (MVPA) at recess; that is, 16.3% to 20.0% of their daily MVPA (comprised between 103.4 [plus or minus] 32.5 min and 113.9 [plus or minus] 32.5 min). This level of activity increased with the increased recess duration. A 1.2% increase of the time spent at recess resulted in a 6.6% increase of their activity (average 23% to 26.5%). It appears that a more appropriate reorganization of school schedule, including recess period and proper physical education classes, may be beneficial for school children to experience adequate amount of physical activity. (Contains 2 figures and 2 tables.) [Abstract provided in both English and French.]