My equivalent of elementary school was primary school, which at the time was grades 1 through 7. I was in diapers through grade 2 and training pants through grade 3 (late potty training), and then I was in diapers from about the second half of grade 6 through the end of primary school.
What did your friends and classmates think of your diapers? When I had friends, they didn't seem to think much about them either way. My classmates were usually horrible about them, but it was more of a general horribleness toward me than a specific "persecute the kid in diapers" campaign.
How did everyone feel once you finished training? I dunno, everyone seemed pretty happy. The first time I was out of diapers, between grade 3 and grade 6, I was fine with it too because I had pretty solid continence. (The second time I got out of diapers my continence wasn't as good, and I was super aware of it, which is ultimately what led me back here.)
Were you accommodated in any way? I don't know if "accommodated" is the word. I was provided with support facilities, but I did have to make sacrifices to access them; I had to go to the school nurse to get changed, and generally I had to either sacrifice some break time or some class time. I was also exempted from some things, like swimming, but I think that was more because they couldn't find an OH&S-compliant way to accommodate me at the time. The two really notable accommodations I got were being able to leave class to be changed whenever it was necessary, and being able to take exams alone.
How did your parents feel about sending you to school in diapers? How did you feel about wearing a diaper? By the time I got to school I had long since failed toilet training (the first time) and there was pretty much an assumption that I was never going to develop continence. I have other developmental disabilities (which I can mask, but couldn't at that age) and I think my parents just counted themselves lucky that I was somehow in a mainstream schooling environment. I was vaguely aware that not many other kids were wearing diapers and that it was weird, but I couldn't really relate that to myself because, like my parents, I just assumed I was never going to leave diapers.
When I had to go back into diapers, my parents, again, assumed it was permanent and seemed pretty chill about it. They did use it as a form of leverage over me but they weren't specifically pissed off at me being incontinent and how "disgusting" it was, just about how much "time" and "energy" I took up (because of circumstances and a dynamic they created). That time, I felt pretty bad about having to wear diapers to school because I had been proud of being toilet-trained and didn't want to have to deal with losing my independence again.
Did you have any classmates who also needed diapers? At the school I was at in grades 1-3, yes, one. At the school I was at in grades 6+, no.