Background: School-based physical education has been associated with a multitude of potential learning outcomes. Representatives of a public health perspective suggest that promoting physical activity in and outside the context of school is an important endeavour. While the importance of behavioural skill training to improve (motor) learning is well documented in both general and physical education, the promotion of behavioural skills to foster physically active lifestyles constitutes a rather neglected area in physical education research. Purpose: To examine whether a standardized physical education-based behavioural skill training program has the potential to positively impact on adolescents' self-reported exercise and sport participation, as well as cognitive antecedents involved in the regulation of exercise and sport behaviour. Research design: Cluster-randomized controlled trial. Methods: A sample of 143 secondary school students (50% girls, aged 14-18 years) attending academic high schools in German-speaking Switzerland were assigned class-wise to the intervention (behavioural skill training) and control condition (conventional physical education lessons). Data were assessed prior and after completion of the 7-week intervention program, which was composed of four 20-min lessons and two reflection phases. Exercise and sport behaviour and cognitive antecedents (exercise/sport intention, motivation, implementation intentions, coping planning, self-efficacy) were assessed via self-reports. A multilevel mixed effects linear regression procedure was used to test the main hypotheses. The regression analyses were adjusted for clustering of school classes, and controlled for baseline levels of the outcome measure and potential confounders. Results: Compared to a control condition, the intervention program resulted in significant improvements with regard to introjected motivation (p < 0.05), coping planning (p < 0.001) and self-efficacy (p < 0.01). The intervention also had a positive impact on adolescents' self-reported sport/exercise behaviour (p < 0.001). Improvements in exercise/sport intention (p < 0.05), coping planning (p < 0.01), and self-efficacy (p < 0.01) were associated with increased levels of self-reported exercise/sport participation. Conclusion: Behavioural skill training as part of compulsory physical education has the potential to improve cognitive antecedents of exercise and sport behaviour and to foster adolescents' exercise and sport participation. Enhancing behavioural skills might be one way in which school physical education can contribute to the creation of more physically active lifestyles among adolescents.