This study focused on adolescents who are studying in middle schools of the Gyeongnam region, aims to provide methods for improving school adjustment among adolescents through the enhancement of family strength. It will examine the effect of family strength on adolescents' school adjustment verify the mediating effect of social support in the influential relationships of school adjustment. The summarizations, obtained in this study are as follows: First, an analysis of the results of the effect of family strength on social support demonstrated that family strength had a positive effect on social support. That is, as family strength was higher, social support increased. Second, an analysis of the results of the effect of family strength on school adjustment show that family strength would have a direct effect on school adjustment, which is positive. Where family strength was higher, school adjustment of adolescents was also higher. Third, the results of the effect of social support on school adjustment when controlling family strength demonstrate that social support would have a positive effect on school adjustment, however, family strength did not predict school adjustment. Therefore, the complete mediating effect of social support in the relationship between family strength and school adjustment was identified. In conclusion, it was identified that family strength had an indirect effect on school adjustment, but not a direct effect. Therefore, it is indicated that indirect intervention through the social support system as well as direct intervention for the improvement of adolescents' school adjustment is required. In addition, it was confirmed that family strength and social support would be more important variables than control variables, which reflect the characteristics of adolescents and family in terms of school adjustment. Therefore, the recognition that the responsibility in adjusting to school is the common role of families, schools, and community going beyond the individual responsibility of adolescents is needed.