This study examined the developmental trajectories of proactive and reactive aggression from 5th to 9th grade in a sample of 126 children (66% male) screened to be in the top 31% on a measure of aggression. Prospective relations between proactive and reactive aggression and delinquency were also examined. Findings suggested that levels of both proactive and reactive aggression peaked in the 6th grade and declined thereafter. Delinquency was stable from 5th to 9th grade. Neither change in proactive nor reactive aggression were associated with overall levels of delinquency from 5th to 9th grade. However, 1-year cross-lagged paths indicated that proactive aggression predicted increases in delinquency, not vice versa. (Contains 3 tables, 2 figures, and 1 footnote.)