To think that the school cannot enforce this uniform rule?

[ReanimatedSGB]

DS started back at school on Friday and has come home with an annoying student handbook full of various pissy instructions and threats of hour-long detentions.
One thing I noticed was that 'boys' hair must be no longer than collar length. DS has long hair. While I completely understand a regulation that long hair must be tied back for school, isn't it actually illegal for them to insist that boys can't have long hair? IE sex discrimination?

let the school get on with teaching.
That's the point - they are taking time away from teaching to fetishise authority. Generally whilst making a big noise about respect and not showing any for either students or parents.