The purpose of this study is to analyze the mediating effects of sense of community on the influence of satisfaction with youth activities on school adjustment among adolescents from the eighth grade to the 11th grade in a longitudinal manner. The study aimed to confirm the longitudinal effects of youth activities on the school adjustment of adolescents and provide basic data for practical plans in the field of youth activities. For these purposes, the investigator made use of the data of the Korean Children & Youth Panel Survey(KCYPS) from 2011 to 2014. Total 2280 eighth graders of 2011 were analyzed in the study. The findings were as follows: there was an increasing trend in the satisfaction with youth activities, sense of community, and school adjustment of adolescents over time with individual differences in the degree of changes. In the early days, sense of community had partial mediating effects between satisfaction with youth activities and school adjustment. In the growth process, the changing rate of sense of community had full mediating effects between that of youth activities and that of school adjustment. These findings point to a sequential process in which satisfaction with youth activities will lead to the cultivation of sense of community, which will in turn promote their school adjustment through its mediating effects. The study also compared boys and girls in differences and found that they shared the same process of sense of community having mediating effects between satisfaction with youth activities and school adjustment. The present study is significant in that it clearly demonstrated the greater importance of a stepwise process of maturity, in which satisfaction with youth activities would affect school adjustment via the mediating effects of sense of community, for growth and change regardless of gender rather than direct relations between satisfaction with youth activities and school adjustment. These findings imply it is important for adolescents to cultivate their sense of community through satisfaction with youth activities for their school adjustment. The present study thus proposed a couple of measures for institutional improvement and program practice for the cultivation of their sense of community.