Honestly, I have no clue whatsoever.
I will duck out of this and observe from a distance. Interesting points put forward so far though.
It's much easier for them to just use disabled toilets or the facilities of the gender that they present as. My friend has worn the male uniform and used the male facilities all the way through his transition at 16.
When I asked him on chat ages ago he said that "As a guy I want to use the guy's toilets not the girl's or special toilets. I'm passable so it shouldn't be a problem. There's always the disabled facilities if someone has a problem with me being there."
Most people on here are probably cis-gender, we should probably be asking trans people what they would prefer instead of trying to decide for them and make decisions based on assumptions of what they want.
I feel like we've fallen into a habit of going very far out of our way to be "accommodating" to people with various first world problems, and it's bordering on being unhealthy. An important part of life is you learning to adapt to your environment rather than vice-versa, and when something isn't quite to your specific standards, to be resilient enough to just "deal with it" yourself instead of putting everyone else out.
I'm not saying that it's a bad thing for a school to cater for its pupils, but it should be proportionate in terms of cost and effort for the school, the number of pupils who will benefit from it, and the extent to which it is truly a necessity.
For example, it's great to have disabled access for people who would otherwise be literally unable to enter the school building. It's not that difficult for a school to have a vegetarian lunch option for the 1 in 20 people who don't eat meat, so they don't go hungry. But insisting that a school goes through the cost and inconvenience of physically constructing new changing facilities or toilets just because one or two pupils out of thousands feel uncomfortable about their gender seems unreasonable to me.
Schools need to raise pupils, not to be overly sensitive and pampered, but to have a balanced give-and-take relationship with the world and remember they're not that special. But recently, it appears that the our culture is shifting towards one of entitlement, where the whims and feelings of the individual are prioritised above all else. The more we continue indulge this, the more people will start to milk it and the more high-maintenance they'll become.
It is easy & done to tell a trans person to go to the changing room according to their gender (e.g if they transition to a female, go to a female bathroom) but there are people who are agender (don't class themselves as any one gender) and people who consider themselves to be both gender - having sex separate bathrooms could make this a really difficult/awkward experience for them, so I'd say a unisex bathroom to make their experience a lot more comfortable
Perhaps unisex able-bodied stand-alone toilets as well as accessible stand-alone toilets and the usual male and female communal toilets?
Would cater well to those that like a bit more privacy when doing their business - me included.