The school setting provides a unique opportunity to promote physical activity in children by ensuring adequate time, appropriate facilities and education guidance is offered. However school uniform design could also limit physical activity. A repeated measures crossover design was used to compare school recess and lunchtime physical activity over four weeks in 64 primary school children (M = 10.48 yrs) when wearing winter uniform or sports uniform. Pedometers recorded step counts during each school recess and lunch break. Perception of the level of intensity of physical activity was also measured using a self-report log book. Mixed model analyses found that girls, but not boys, were significantly more active at recess (p = 0.03), lunch (p = 0.04) and overall (p = 0.006) when wearing their sports uniform compared to their winter uniform. School uniform did not impact the boy's physical activity levels. Perceived intensity of physical activity increased slightly among both girls and boys. A physically restrictive school uniform has the potential to inhibit physical activity among primary-school-aged girls. (Contains 3 tables and 2 figures.)