Background and Aims It is clear that measuring physical activity (PA) in children is a major challenge and Accelerometers are useful instruments for this reason. The aims of this study were to measure PA pattern of student by accelerometer and to evaluate differences by gender and age.

Methods The sample for present study comprised 270 children (boys n=119 and girls n=151), aged 6 to 9 years old. The GT3X activity monitor was used as an objective measure of daily PA. Each student was scheduled to wear the accelerometer during the week of monitoring.

Results The mean overall activity was higher in boys than in girls, but this difference was significant only on weekdays (P<0.05). Overall PA was significantly correlated with age both in whole week (P<0.01) and weekends (P<0.001).

Conclusion Our findings are important for a better understanding of PA pattern in students of Tehran city, which is essential for education and health promotion. The results show that boys are more active than girls.