This study examined the development of adolescent self-reported instrumental-overt, instrumental-relational, reactive-overt, and reactive-relational aggression during middle school ("N" = 384; 12-14 years; 53% boys). Growth modeling indicated average increases in instrumental-relational aggression, and decreases in reactive-overt and reactive-instrumental aggression over time. Further, overt and relational aggression driven by reactive reasons (functions) predicted gains in aggression driven by instrumental reasons, and overt form of aggression predicted increases in relational form of aggression across time.