School didn’t start until after labor day and ended in May. We also had a wall of windows that the teacher would open out. I don’t remember it ever being hot in class. The buildings were designed for better ventilation IMO.
Even in September and May, it can still be pretty hot but you’re right, I don’t remember ever suffering. I guess we had our minds on other things back then :-)
In the house, we had two window units. We usually only ran the one at night on the east side of the house that cooled the bedrooms. I don’t remember many times having them both going.