The purpose of this study was to examine the mediating role of classroom climate between teacher attachment and school adjustment. Moreover, it also investigated peer attachment’s moderated mediating role. In particular, we aimed to expand and test a moderated mediation model by adding peer attachment as a moderating variable not only in the relationship between teacher attachment and classroom climate but also between teacher attachment and school adjustment. For this study, 505 sixth-graders (260 male, 245 female) from a metropolitan area completed self-report questionnaires and their data were analyzed. First, classroom climate partially mediated the effect of teacher attachment on school adjustment. Second, the moderation effect of peer attachment was only valid on the relationship between teacher attachment and classroom climate. Finally, it was confirmed that as the level of peer attachment increased, the indirect effect of teacher attachment on school adjustment, mediated by classroom climate, became stronger. This study integratively verified the major school variables affecting elementary school students’ school adjustment. Based on these results, we discuss the implications and significance for education and school counseling, and offer suggestions for future research.