Preschool-aged children are not meeting national physical activity recommendations. This study compares preschoolers' physical activity engagement during two different physical activity opportunities: outdoor free play or a structured movement session. Eighty-seven children served as participants: 40 children participated in outdoor free play and another 47 children participated in a planned movement session. Children in the movement program replaced their outdoor free play with a structured movement session on 2 days each week. All movement opportunities were 30-min in duration. Physical activity was objectively measured using accelerometers. Results show that, compared to children on the playground, children in the movement program engaged in less sedentary behaviors and more light, moderate, vigorous and moderate to vigorous physical activity. In total, children in the movement program engaged in 15.5 min of healthier physical activity behaviors as compared with children in the outdoor free play. Structured movement time appears to afford children an opportunity to engage in more physical activity than outdoor time alone. Findings support that preschool centers should provide children with a daily structured movement time that includes formalized instruction in addition to regularly scheduled outdoor free play. (author abstract)