That’s nothing to do with boys being more badly behaved, it’s as I’ve said before – sex (and race) discrimination.
I agree with those Headteachers who say that fines would only penalise pupils remaining at the school, the answer is to make the individual (Head)teachers responsible for their own actions by fining or gaoling them.
When schools are being run by people who clearly have no respect for the law, nor even basic human rights, it’s not surprising when their students develop a similar attitude.