The purpose of this study was (a) to test a hypothesized model of motivation grounded in the Self-Determination Theory within the context of conceptual physical education (CPE), and (b) to explore the strength and directionality of perceived competence for physical activity as a possible mediator for health-related fitness knowledge and actual physical activity behaviors. Participants were 280 high school students who were at the end of a CPE course. Participants completed the Behavioural Regulation in Exercise Questionnaire–2, the Godin Leisure–Time Exercise Questionnaire, the Perceived Competence Scale, and a Health-Related Fitness Knowledge Questionnaire. Structural equation modeling analysis was used to explore the relationships between the variables of health-related fitness knowledge, perceived competence, motivation, and physical activity. The analysis resulted in a modified model that showed a relationship between perceived competence and physical activity, mediated by introjected and identified regulation. Implications and recommendations for physical education professionals are made.