The purposes of this study were to determine whether two forms of moral reasoning commonly found in early elementary school, self-oriented and psychological needs-oriented, are related to both current and future aggression. A total of 132 students participated in a study that began when they were in first or second grade and concluded 2 years later. Concurrent and longitudinal relations were found for overt aggression, and for both reactive and proactive functions of aggression. Psychological needs-oriented reasoning in early elementary school predicted aggression in later elementary school. Moral reasoning did not moderate the stability of aggression over time, however. Results have implications for school discipline practices and violence prevention and intervention programs. (Published Abstract)