This study tested a novel approach to capitalizing on the benefits of play for informal math learning. Two experiments evaluated a platform called "Fraction Ball," that provides an embodied, playful, and physically active learning experience by modifying the lines on a basketball court to support rational number learning. In the Pilot Experiment, 69 fifth-sixth graders were randomly assigned to play a set of four different Fraction Ball games or attend normal physical education (PE) class and completed rational number pretests and posttests. After strategic improvements to expand the intervention, the same protocol was implemented in the Efficacy Experiment with 160 fourth-sixth graders. Playing Fraction Ball for four PE class periods (Pilot Experiment) improved students' ability to convert fractions to decimals. Playing a revised version of six different Fraction Ball games for six PE class periods (Efficacy Experiment) significantly improved children's rational number understanding as reflected by higher scores in overall accuracy, with positive impacts on several subtests. Fraction Ball represents a low-cost, highly scalable intervention that promotes math learning in a fun and engaging approach.