Let's try this:
Let's say someone in the boys' locker room had a horrible skin condition - makes his back break out in awful, pustule-filled boils that make anyone who looks at them want to vomit.  Literally vomit.  Doctors, nurses, members of the opposite sex, and any boys/men in a locker room with him.  Does he have the right to use the locker room?  And in so doing, is he interfering with other people's right to not be upset and/or vomit by being in there?
		
		
	 
I think in this case the child wouldn't be going to school.  I think that qualifying as a sick day.....
		
 
		
	 
Nah, constant skin condition.  Can't be helped.  Always activated.  Looks awful.
		
 
		
	 
Well, thank god we are discussing things that are not the outliers.  Just to check, the people only feel like vomiting, but not actually vomit.  If people actually vomit, that would be an environmental hazard and the school would have a duty to make sure the spread of disease would not occur.  Now, if we are talking about "
feeling like vomiting" the the school could make arrangements for either the student to change elsewhere, or have the other students that have issues change elsewhere.
Now I am sure you will bring the argument back to "what if this was just because the one student was black and the other students feel X."  Totally different situation.  Normal people do not feel sick because of another person's skin color.
Riddle me this... A thirty-ish year old man, for some reason 
thinks he is a 15 year old girl that should be going to school.  He wears a wig and dresses in that damn sexy Catholic School Girl white top, plaid skirt and the Tucker + Tate shoes with the canvas upper and lining with a rubber sole (extra description for Arizona Ron).  He even says "like" waaaaaay too much.  Does he get to go to school and change in the girls locker room?