I never went to an air conditioned school, and the hallways outside the classroom were lined with lockers. Sounds like the scenario you're describing. Unless there's something really weird going on there, except for early school year and late school year when outside temperatures get to 80 or 90, 90 degrees still sounds awful hot, even if you have a locker near the ceiling. (We had two-tier lockers - one set two or three feet high, a divider, the next set another two or three feet. I had upper-tier lockers a few times.)

And even then, bagged lunches were edible. In grade school, there was no option - there was no cafeteria, no food served. If they had a poverty program back then, those kids got sandwiches and cookies-n-stuff just like the rest of us brought to school.