OBJECTIVE Physical activity (PA) and fundamental motor skills are important components of current and future trajectories of health in young children. This study examined the effects of a 5-week motor skill intervention on preschoolers' motor skill competence and their PA behaviors while participating in the motor skill intervention or outdoor free play (recess). METHODS A total of 102 preschoolers served as participants and were part of a motor skill intervention group (n = 64) or a control/outdoor free play group (n = 38). Children's motor skills were assessed before and after the intervention using the Test of Gross Motor Development-3rd edition. PA during the motor skill intervention and outdoor free play was assessed using accelerometers both immediately before the start (baseline, Week 0 or Week 1) and end (late, Week 5 or Week 6) of the intervention. RESULTS All children significantly improved their motor skills from baseline to late assessment (p < 0.05). Children in the motor skill intervention demonstrated greater rates of change (p < 0.001) and scored higher on all motor skills at the late assessment compared with the control group (p < 0.001). There was no effect of group (control vs. intervention), but there was a significant effect of sex on children's PA during outdoor free play at baseline (p < 0.05). Similarly, there was no effect of group on PA during days with the movement program (intervention vs. outdoor free play) at either time point, but boys were more active than girls at the late assessment (p < 0.05). Last, children in the intervention engaged in more PA while participating in the intervention toward the end of the intervention than at the beginning. CONCLUSIONS The 5-week motor skill intervention was effective at improving preschoolers' motor skills and rates of change in motor skills were higher for children who completed the intervention compared with children in the control group. Preschoolers in the intervention did demonstrate PA changes while participating in the intervention, but these changes did not translate outside of the intervention setting.