This article addresses the ethical and motivational dimensions of punishment in schools, focusing on the idea of a just school community. Lawrence Kohlberg's account of a just school community is examined and systematically revised to reflect advances in psychology and a more adequate conceptualization of justice. A eudaimonic conception of justice is articulated with respect to five distinct dimensions of a just school community. This is informed by Self-determination Theory (SDT) and an account of the basis of educational authority over minor children. The resulting account of a eudaimonically just school community clarifies the limited value of punishments as motivators and the importance of needs-support to enlisting students' cooperation. It resists the growing reliance on criminal justice responses to student misconduct and holds that discipline and punishment in schools should be diagnostic, educative, restorative, and community building.