Because there are schools and school systems where the treatment of girls was much closer to the treatment of boys than others. If it was true that schools would have been better off treating girls and boys identically, these schools and school systems would have achieved better outcomes than the ones where different treatment was in use. Instead the opposite was true.
I think it took more than a couple of years, there was over a decade to compare decline before CP in private schools ceased.
No, it didn’t take more than a couple of years. The decline can be seen in data two years after abolition.
Parenting, Social conditions, children’s rights and the schools themselves , have changed considerably; all have an impact on children’s approach to authority and behaviour.