Background: Children’s executive functions develop rapidly during the preschool years and are critical for attending to lessons and meeting classroom expectations. Engaging in periods of outdoor play that have lower regulatory requirements and that provide opportunities for physical activity may help children maintain control over their behavior when they are back in settings with higher regulatory requirements. However, little work has formally examined this proposition in early childhood. Methods: This study used a quasi-experimental design to examine preschoolers’ executive functions following indoor compared to outdoor play. A total of 72 children (mean age = 4.5 years, 46% female, 73% non-Hispanic White) participated in task-based assessments of attention shifting and inhibitory control and in classroom observations of attention and inhibitory control. A subsample of the children (n = 51) was assessed for physical activity using accelerometry to examine the extent to which young children’s physical activity during outdoor play predicted their subsequent executive functions better than their physical activity during indoor play. Results: Children showed greater attention during classroom circle time following outdoor play compared to after indoor play (d = .34). Children’s non-sedentary activity during indoor play was not related to their subsequen task-based executive functions but showed negative associations with their subsequent classroom-based executive functions. Children’s percentage of time spent in non-sedentary physical activity during outdoor play showed a quadratic association with subsequent task-based inhibitory control but linear associations with subsequent classroom-based attention and inhibitory control during circle time. Conclusion: Periods of outdoor play that involve recommended amounts of physical activity may help young children engage executive functions when they return to the classroom. (author abstract)