Yeah I mean it was a mile to school for me and I started walking there in kindergaten with my brother as the supervisor. He's almost 2 years older than me, so we were kike 5 & 7. All the kids we knew would walk to and from school, if they brought a bike they'd have a lock fot it and obviously have to remember their house keys everyday, you can't just leave the house unlocked everywhere (depending on the parents). Where I was at schools were constantly expanding do to population growth, so there were always portables ("temporary" classrooms outside the main buildings that were essentially cheap manufactured homes).

I can 100% see a teacher giving spare keys to whomever they thought was going to get their first so they could turn down the AC because they weren't supposed to keep it at moderate temperatures all afternoon/night. Extremely hot temperature days in portables were the worst. To be honest though I seem to remember that the portable I had in 5th grade you just pulled the door witg or without the key and it had enough flex on the door/wall that it would just pop open. (Think someone skimped out on some fasteners).