School climate is the quality and character of school life and reflects the norms, goals, values, interpersonal relationships, teaching and learning practices, and the organizational structure of a school. There is substantial literature documenting the negative association between positive school climate and adolescent delinquency, but little is known about the moderating and mediating mechanisms underlying this relationship. The aim of this study was to examine whether the direct and indirect pathways between school climate and adolescent delinquency would be moderated by effortful control. A sample of 2,758 Chinese adolescents (M age = 13.53 years, SD = 1.06) from 10 middle schools completed anonymous questionnaires regarding school climate, effortful control, deviant peer affiliation, and delinquency. After gender, age, geographical area, and socioeconomic status were included as covariates, the results revealed that school climate was significantly associated with adolescent delinquent behavior. This direct association was moderated by effortful control, such that the negative relationship between positive school climate and delinquency was only significant among adolescents low in effortful control. Moreover, the indirect association between school climate and delinquency via deviant peer affiliation was also moderated by effortful control. Specifically, the moderating effect of effortful control was not only manifested in the relationship between school climate and deviant peer affiliation, but also in the relationship between deviant peer affiliation and delinquency. These findings contribute to understanding the mechanisms through which positive school climate might reduce delinquent behavior and have important implications for prevention efforts aimed at diminishing adolescent delinquency.