The thing is, if half the boys said they identified as girls, where is the line drawn? One boy to change with the girls, apparently fine. Two boys, still fine? Ten?
It's great this boy is being supported with his feelings. I work with a boy who wears a skirt to school and says he's a girl, he's year 3. We are careful to allow him to choose if the class is being split into boys and girls for some reason (not changing, I think they're still together for changing atm). But when they go swimming next term? I can't imagine he'll be changing with the girls.
What would the school do if a parent insisted their daughter, who wears trousers to school and likes "boy things", wants to change with the boys? I cannot see them allowing her to change under a poncho in the boys' changing room.
At the end of the day, regardless of who wants to get changed where, you will never be able to please everyone.
So surely it makes sense that the school looks to please the girls in this scenario (15 of them?) by keeping their changing room girls only, and if this boy genuinely doesn't want to change with the boys for fear of bullying, he changes in a separate cubicle, therefore his feelings are being acknowledged.
Just wanting to change elsewhere does not mean it should happen. I've taken school groups swimming and some children don't want to be in a room with other children to change full stop. But if you make allowances for one to change in a cubicle, you'd have to do it for all.
This is making an allowance for one but not considering others and just saying "This is how it'll be so tough". That's not acceptable, regardless of the fact we're talking about sexes.
(Sorry, just thoughts on a page - this has really got me thinking!)