The purpose of this study was to examine the effects of a class-wide conflict resolution program on fifth-grade students in a primary school, focusing on changes in selfefficacy and school adjustment. The conflict resolution program comprised five 45-minute sessions. We believed compact program is suitable for school education in Japan. The results showed that (1) the program enhanced participants' self-efficacy, especially in those with lower initial levels of self-efficacy, and (2) the program improved only one factor of school adjustment, "greeting." In addition, the hypothesis that the program's enhancement of self-efficacy would promote improvement in school adjustment was examined using regression analysis. we also found more factors of school adjustment were affected by selfefficacy at the post-test compared to the pre-test. These results shows hypothesis was partially supported. We discussed not only the effects of peer mediation program compact but further research would be needed to clarify the mechanisms underlying these effects.