Objectives: Evidence supports that girls are less proficient than boys at performing ball skills. This study examined the immediate and long-term effects of a ball skill intervention on preschool-age girls' ball skill performance. Design: Randomized controlled trial. Methods: Girls (M-age = 47.24 +/- 7.38 months) were randomly assigned to a high autonomy, mastery-based 9-week motor skill intervention (the Children's Health Activity Motor Program; CHAMP, 540 min; n =38) or a control group (free-play; n =16). Ball skill proficiency was assessed at pretest, posttest, and retention test (after 9 weeks) using the object control subscale of the Test of Gross Motor Development-2nd Edition. Treatment efficacy was examined using linear mixed models. Two models were fit: one for short-term changes (pretest to posttest) and one for long-term changes (pretest to retention). Results: Linear mixed models revealed a significantly time*treatment interaction for both models. Post hoc analysis confirmed that girls in CHAMP experienced significant gains in ball skills from pretest to posttest (p < .001) and pretest to retention (p.05) but had significantly higher ball skills scores at both posttest (p < .001) and retention (p < .001). Conclusions: This study demonstrates the positive effects of a ball skill intervention (i.e., CHAMP) on improving girls' ball skills both short- and long-term. Findings suggest that early childhood interventions that focus on the development of ball skills in young girls might be an avenue to improve girls' ball skill performance. (C) 2016 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.