Looking at a current thread on AIBU there seems to be a huge problem in some secondary schools in terms of access to toilets generally, whether sex-segregated or not.
www.mumsnet.com/Talk/am_i_being_unreasonable/3808579-to-think-this-school-policy-is-really-odd?
This is not just the school mentioned in the OP as other parents and teachers are reporting similar issues, ie.
- toilets being locked either during lesson times or during break times and lunch time;
- pupils only being allowed to go to the toilet during lesson times if they have a medical condition;
- pupils having to be accompanied by a member of staff to use the toilet during lesson time (by the Head Teacher at times!)
- only being allowed 2 minutes to use the toilet as standard.
In the OP post school, other posters have worked out that at lunch time there are only 4 toilets available for 600 girls. (I think similar for boys.)
Another poster worked out that the restrictions on access outside of lesson periods and the ratio of toilets to pupils means that if you only allowed 1 minute per toilet visit that 2/3 pupils would not have access to toilets at all during the day.
The reasons for supervised access to toilets mentioned on that thread by teachers include: vandalism, bullying, knife crime, drug taking, "prostitution", sexual assaults.
There is a bit of discussion about gender neutral toilets (both for and against) but the main issue is severely restricted access and that, although bad for both, that this is affecting girls more than boys.
I did not see anyone on that thread sharing the information on standards and legislation that has been brought to this thread.
It might therefore be that it is only when issues of sex-segregation are raised, as in this thread, that problems with access to toilets generally in a school are brought to light and dealt with properly. Along with attention to the worrying issues that are leading to restricted access??