Purpose: The purpose of this study was to explore how parent involvement influenced the effectiveness of a movement intervention targeting gross motor skills and physical activity behavior in preschool-aged boys and girls. Methods: Parents received training at monthly school-based sessions and online to implement the movement intervention once per month at school and once per week at home across 6 months (N = 104; M_age = 48.30 months, SD = 6.90). Children completed the Test of Gross Motor Development-3 at baseline and wore physical activity trackers 24/7 for six weeks during the intervention. COVID-19 disrupted the intervention and prevented immediate post testing. Children (N = 60; M_age = 60.86 months, SD = 6.57) who returned to the center one year later completed gross motor skill retention testing. Results: For each additional school-based session attended by the parents (up to six), children's locomotor and manipulative skills were 1.87 and 1.95 points higher, respectively, at the start of the following academic year. For physical activity, each session increase in attendance at the school-based component of the intervention resulted in an additional 1455 steps in average weekly step count. Conclusion: Increased parent engagement demonstrated greater change in gross motor skills and larger acute physical activity responses. Understanding barriers that impact the level of parental intervention engagement (i.e., dose) also provides insight into why some children learn and others do not within a parent-led intervention. Although the implementation and results of this study were impacted by COVID, these data can help researchers optimize future intervention strategies.