I don't care about the bathroom aspect, as there are stalls for privacy. But the locker room aspect troubles me. Not all locker rooms have stalls. DD is in a dance group which has 35-50 girls changing at one time in a single room with mirrored walls. They all turn "butt out" for some semblance of privacy, but if you look up and see the mirror, you get a full view of everything, because they disrobe completely. Totally naked. Some of them have no trouble with modesty, and some are still very uncomfortable and just struggle through it. And that is with all females in the room. So far, a boy hasn't tried out for the team, but one could since there are no rules against it. And other locker rooms like this one exist for sports. Big old open locker rooms with no privacy stalls.
It is not practical to provide a private changing area to the modest girls/boys. They will outnumber the (probably) single transgender student. Schools don't have the space or money to add all those changing rooms. If 20-30% of the class decides they want to have privacy and there is only one privacy stall, they may never get changed and ready for class on time. In any other scenario, someone of the opposite sex exposing genitalia to minors would be a crime, but now it's all good? We need to stop and take a breath on this one and think. A compromise is in order and in this case, a separate changing room for transgender students is the most practical solution, even though the Dept. of Education says otherwise.
It's not that I don't have sympathy for transgender students. But tolerance runs both ways and the modest students who don't want to change in front of someone of the opposite sex (not gender) are not unreasonable. They should not be made to feel like they are awful if they are less than enthusiastic about the new policy.