We also didn't have A/C in our schools, but I was miserable and lethargic from the heat and humidity a few months of the year. Needless to say, my schoolwork was not up to par during those times. On extremely hot/humid days, I'd come home from school feeling nauseous. Some kids dealt with heat better than others.
During summer vacations, I'd spend a lot of time in the basement of our house, because that was the coolest spot in the house. My mother used to try and get me to go outdoors and play, but it was too hot for me. If my little pals wanted to play with me, they had to come to the basement!
(P.S.: It was a finished basement, with a tv, toys, books, and a sofa.)