This paper aims to test the direct predictors of the theory of planned behaviour (TPB), action planning and coping planning as predictors of changes in physical activity (PA) in 157 adolescents (mean age: 12). TPB measures, the Action Planning and Coping Planning Scales (APCPS) and the International Physical Activity Questionnaires were measured at baseline, 2- and 5-month follow-up. Hierarchical regression analyses were conducted regressing PA at Time 2 or Time 3 onto TPB and APCPS at baseline or Time 2, respectively. Past behaviour accounted for a significant 25-51% of the variance in PA in Step 1 of all three analyses. In Step 2, TPB accounted for an additional 3-10% with intention as a significant predictor. While no main effects for action planning or coping planning (Step 3) were found, all three analyses resulted in a significant amount of incremental variance accounted for by the interaction of action planning and coping planning (Step 4). Results suggest that the combination of high levels of action planning and coping planning is associated with increases in PA. Implications for theory of behaviour change in adolescents are discussed.