Recent research has suggested that the effects of sport on well-being are mediated by psychological characteristics such as physical self-concept, instrumentality and positive body images; in addition, sport was found to be related to these psychological benefits for high school girls. However, physical self-concept played a central role by mediating the sport -body image and sport instrumentality relationships. Positive body image and instrumentality, in turn, predicted greater psychological well-being. The purpose of this investigation was to replicate earlier studies, and to examine these relationships with non-sport physical activity. Sport and physical activity were expected to contribute to higher physical self-concept, which in turn, would contribute positively to instrumentality and body image. Further, instrumentality and body image would be positively related to psychological well-being. Participants were 355 9th (n = 170) and 10th (n = 193) graders and they completed measures of involvement in sport/physical activities, physical self-concept, instrumentality, body satisfaction, self-esteem, satisfaction with life, depression, and demographics. Structural equation modeling was utilized to analyze the data. Overall, for both sport and physical activity, the models fit the data well (sport model: NNFI=.95, CFI=.96, SRMR=.08, RMSEA=.09, physical activity model: NNFI=.96, CFI=.97, SRMR=.08, RMSEA=.09). Specifically, sport participation was positively related to physical …