Violence in Australian schools is perceived to be on the increase and most of this violence is said to be caused by boys. The traditional view is that males are the more aggressive sex. Recent research in Scandinavia (Bjorkqvist, Lagerspetz and Kaukiainen, 1992; Bjorkqvist, Osterman and Lagerspetz, 1994a) however, has questioned this gender polarised view of aggression in suggesting that gender differences may be qualitative rather than quantitative. This paper reports a study of gender and developmental differences in aggression among students in South Australian schools. A modified version of a peer estimation technique, the Direct and Indirect Aggression Scales (Bjorkqvist et al., 1994a), was administered to students across four year levels (years 2, 6, 9 and 11) in two Catholic high schools and four Catholic primary schools. Boys were found to be more physically and verbally aggressive than girls but girls used more indirect aggression at the higher year levels. The practical and research implications of these results are discussed.