This is one of the most concerning aspects of the current trans campaign for me.
I remember how embarrassing I found it as a teen having to change in front of my female peers. Having a male in there, however trans identifying, would have been a weekly horror. I'm not sure I'd have been brave enough to opt out on my own as I wouldn't have wanted to offend the person.
Have anyone's kids experienced this with a school following Mermaids type advice to let the trans child choose, and if so what did they choose? If transgirl chose to share with girls, did many girls then ask for alternative changing?