This study investigated whether 6 weeks of basketball combined with mathematics once a week in physical education lessons could improve children's motivation for mathematics. Seven hundred fifty-seven children were randomly selected to have either basketball combined with mathematics once a week or to have basketball sessions without mathematics. Children in BM and CON motivation for classroom-based mathematics were measured using the Academic Self-Regulation Questionnaire before and after the intervention. Among the BM, levels of intrinsic motivation, feelings of competence, and autonomy (...) were measured using the Post-Experimental Intrinsic Motivation Inventory questionnaire acutely after a basketball session combined with mathematics and immediately after a session of classroom-based mathematics. BM had significantly higher acute levels of perceived autonomy, competencies, and intrinsic motivation during basketball sessions combined with mathematics compared to when having classroom-based mathematics. A significant decrease in the mean for intrinsic motivation was observed from T0 to T1 for CON, but not for BM. BM had a more positive development in intrinsic motivation compared to CON from T0 to T1, meaning that BM had a positive influence on children's intrinsic motivation for classroom-based mathematics. This study indicates that basketball combined with mathematics is an intrinsically motivating way to practice mathematics, which also has a positive influence on children's general intrinsic motivation for mathematics in the classroom. (shrink)