Disruptive behaviour disorders are much more common in boys than girls (Office of National Statistics, 1999); in contrast, gender differences in normative problem behaviours are poorly understood. To address this issue, 228 6-year-olds (134 boys, 94 girls) were each observed playing a board game with a same-gender friend. Ratings of aggression, disruption, arousal and negativity were used to index problem behaviours. Multiple-groups confirmatory factor analyses demonstrated that the latent factor had the same metric for boys and girls, but a mean that was approximately half a standard deviation higher for boys than girls. In addition, the association between the latent factor and teachers' ratings of total difficulties was significantly stronger for boys than girls.