Equally, I don’t believe that in principle it must be the case that misbehaviour levels must necessarily be equal. We know that in many animal species there are different behaviour patterns for males and females, and this is surely genetically determined. So it is at least in principle possible that there could be similar differences in human behaviour. Of course human genetic differences are overlaid by differences in socialization in the home, and so behavioural differences between girls and boys at school, if indeed they exist, could equally well be determined by prior experiences.
The arguent about fairness is, of course, quite different. One could say that the same offence should be dealt with by the same punishment, on grounds of fairness, even if one accepts that there are significant differences in behaviour between boys and girls, or indeed between any other well-defined groups of children.