The purpose of the present study was to test a Self-Determination Theory (SDT) process model in relation to involvement in physical activity and competitive performance among students (N = 190). In this model, perceived autonomy support from teachers and coaches was expected to be positively related to autonomous motivation, perceived competence, harmonious passion and action orientation, and that they would be positively related to involvement in physical activity and competitive performance. In using LISREL to test the model, autonomy support was positively linked with perceived competence, autonomous motivation, and action orientation. In turn, perceived competence (through harmonious passion), autonomous motivation, and action orientation were all positively associated with involvement in physical activity, whereas perceived competence and autonomous motivation were positively correlated with competitive performance. (Contains 3 tables, 2 figures, and 1 footnote.)