The aim of this study was to determine the extent to which guided throwing practice volume influenced gains in throwing competency in young children during exposure to a mastery motivational climate physical play program. Fifty-four preschool children attended 13 biweekly 30-minute motor skill sessions over 7 weeks. Pre- and post-test throwing competency was measured in three ways (Test of Gross and Motor Development–Third Edition [TGMD-3], developmental sequence for throwing, and throwing velocity). Throwing practice behaviors (visits, time, and trials) were then coded for each participant using video recordings. Paired-samples t-tests revealed significant gains in throwing proficiency by the children from pre- to post-test on all three measures. Results from multiple hierarchical linear regressions highlighted that pre-test scores and guided throwing practice volume (a principle component analysis of throwing visits, time, and trials) accounted for 19% (TGMD), 52% (developmental sequence), and 60% (velocity) of the explained variance of post-test throwing competency, respectively. Results also revealed that although boys spent more time practicing throwing than girls, gender only appeared to be a significant predictor in the TGMD regression model. These findings provide empirical evidence of the importance of guided practice during mastery climate programs.