Physical activity (PA) promotion for youth has long been thought of as a public health issue. However, with increases in diseases associated with a sedentary lifestyle and the known benefits of PA, increasing the PA levels of children and adolescents has become a major public health concern. To this end, numerous organizations are calling on schools to take a leadership role in youth PA promotion. Prior to developing and evaluating interventions, it is important to understand the amount of PA children accumulate during the school day and across the school year. It is also important to understand the role of season on children's PA, including school-day PA. While some argued that seasonality has a limited role in children's PA levels, others found children are more active when the weather is more conducive to outdoor activity. However, little is known about the impact of seasonality on children's school PA. The purpose of this study was to examine children's number of steps during school and out-of-school in fall and winter. The authors also examined the differences between steps while at school (school steps) and total daily steps on school days (daily steps) during the two seasons. A better understanding of these differences may help better prioritize intervention or school resources to locations and seasons identified as low active. This study was the first to examine differences between school and out-of-school steps. The authors' findings are consistent with previous seasonality research, with children having higher daily activity in fall, when the weather was suitable for outside PA, than in winter when temperatures were much lower. (Contains 2 tables.)