but 'provision where it is needed' seems to depend on the individual child/or their parent making a personal appeal to their teacher or the head. Many children would be too embarrassed to do this.
Who are you to decide about 'the majority of cases?' This thread has numerous examples, starting from the OP onwards, who have said that their child/their classmates do feel awkward or embarrassed about the situation. Others (including myself) remember being unhappy about it from our schooling years ago, which suggests it was upsetting enough to stick in the memory.
Several of these posters said that either the children have not mentioned it to their parents, or that they have, and then raised it with the school, but nothing has happened. Obviously anecdote is not evidence, but this does suggest that there are lots of children out there are very unhappy changing but are too embarrassed to mention it.
and incidentally I have been in a number of modern classrooms over the last few years - ranging from old Victorian, to tiny 50s pre-fab style, to purpose built, and yes, while they have been overcrowded, I think I could have fit a screen/two in there. I'm sorry if I'm not describing the type of thing I mean clearly, and of course some classrooms could be exceptionally crowded, but the point I keep repeating is that, for the majority of cases, these issues could be worked around IF the teachers wanted to. However it seems that some posters refuse to see that it is an issue, so, I guess we'll never agree.