Aggressive behaviour of children aged 6-11: gender differences and their magnitude.

A total of 72 boys and 72 girls, of six age groups from 6 to 11 years, was observed in the school classroom over eight 5-minute periods, under conditions of low structure, non-directive teaching; aggressive and other categories of behaviour were recorded. There were no overall gender differences in aggression, but boys showed significantly more physical aggression than girls (overall effect size d = 0.36), whereas girls showed significantly more verbal aggression than boys (overall effect size d = 0.66). The physical aggression difference was variable both in direction and magnitude across the age categories and included a large reversal at 9 years. Boy's higher levels of physical aggression were not associated with higher levels of activity or more time spent in social interactions. The gender difference in verbal aggression was consistent in direction and magnitude across age categories, but in the opposite direction to the majority of previous findings. There were no gender differences in other categories of verbal behaviour.