When you’ve gotta go, you’ve gotta go. It’s so true that it’s become a cliché. Our bodies don’t work on a tight schedule, and sometimes you have to head to the bathroom, even if you’re in the middle of a very important calculus explanation. Your teacher might want you to stick around, but they probably don’t want to have to deal with a puddle in the middle of their classroom.
As much as teachers and school boards would like everything to run like clockwork, they’re dealing with human beings, and even less predictably, juvenile human beings. Why not just make it easier on everyone and let kids pee when they need to, instead of shaming a perfectly normal bodily function? It turns out even teachers need to learn some manners.