The purpose of this study was to determine the amount of physical activity in which children engage during physical education classes and factors that mediate their participation. Third and 4th grade students wore pedometers during each 30-min physical education class for one school year. Steps per class were collected daily during structured and unstructured (recess) days, and during inside and outside physical education lessons. Factorial ANOVA revealed third and fourth grade boys took significantly more steps than third and fourth grade girls, and those involved in youth sports accumulated more steps during a 30-min physical education class compared to those who were not involved in youth sports. Dependent t tests verified steps accumulated during classes held outside were significantly greater compared to those accumulated during classes held inside, and steps accumulated on free (recess) days were significantly greater compared to those accumulated on structured days. The results highlight the need for recognition of the contexts of gender and youth sport participation when planning and implementing an appropriate physical education experience for children. (Contains 2 tables and 3 figures.)