Ridiculous, I've worked as a teacher for 10 years and we have had many ways of changing in different schools but I would not expect children of that age to get changed in front of the opposite sex.
School 1 - I taught Year 5. School had a new hall with fancy changing rooms. The boys went into the boys changing rooms, the girls into the girls changing room while I stood in the hall. Any messing around that child or children were sent to the toilets to change by themselves.
School 2 - I taught Year 6. Older building so no dedicated changing rooms. I worked this a couple of ways. The first couple of years children went in small groups and got changed in toilets the preceding lesson. (Obviously at a time when children were working quietly).
Later on my partner teacher was a male and we both did PE between break and lunch on the same day so all the girls would come into my room and the boys would go into his room and we would stand at our respective doors in the corridor and chat with a foot in the door so it was still but the children felt comfortable.
Current school. I now teach Year 1 so different kettle of fish but in this school the children just come in in their PE clothes on their assigned PE days. Usually have PE in the afternoon (especially the older classes) so they can go home and change after after activity. By far the best system. Children are comfortable, no learning time is taken up with children getting changed or the inevitable drama.
I know it's a long message but my main point is there are many ways around this and children that age have so much going on in their heads the last thing they need to worry about is getting changed in front of their peers of the opposite sex