The purpose of this study was to investigate the associations among predisposing (perceived competence and enjoyment), reinforcing (social environments), enabling factors (motor skills, fitness, physical environments) and physical activity among 288 children, and to identify the age and gender differences among participants. The children completed previously validated questionnaires assessing their perceived competence, enjoyment, school social and physical environments, and physical activity. Physical fitness was measured by FITNESSGRAM fitness testing. Students' motor skills were assessed by PE Metrics. The results indicated that perceived competence and enjoyment predicted physical activity for boys, while perceived competence was the only predictor for girls. Age effects for fitness and skill were significant, as were gender differences for skill, social environment and perceived competence. This study suggests the importance of supportive teachers who provide enjoyable physical education that builds perceived competence for children to improve fitness, motor skill development and physical activity participation. The results support associations between predisposing factors and self-reported physical activity as theorized within the social ecological model