Objective: This study tested effects of changes in the psychological constructs of the trans-contextual model (TCM) on changes in adolescents’ outside of school moderate-to-vigorous physical activity (PA) measured using self-report and accelerometer-based device. Design: A three-wave longitudinal design was used. High school students (N = 331) completed measures of all the TCM constructs at Time1 and at Time2, five weeks apart. Self-reported PA behaviour was measured also at Time3, five weeks after Time2. PA was measured using accelerometer-based devices for seven days following Time1 and Time3 for a census week. Results: A structural equation model using residual change scores revealed that perceived autonomy support from physical education (PE) teachers positively predicted autonomous motivation in PE. Autonomous motivation in PE positively predicted autonomous motivation in leisure time. Leisure-time autonomous motivation was positively and indirectly related to intention, mediated by attitude and perceived behavioural control. Intention positively predicted self-reported PA, and mediated the effect of autonomous motivation on self-reported PA. There were no effects on outside of school PA measured by accelerometer-based device. Conclusions: Results provide qualified support for the TCM in the prediction of change in adolescents’ leisure-time autonomous motivation, intention, and self-reported PA, but not change in PA measured by accelerometer-based device.