"I study geography in school."
Translation:Jag studerar geografi i skolan.
Thanks for your reply. However, på skolan does have much wider use than quite literally on top of the school roof. Some examples from the web:
Fest på skolan
en konlikt ... på skolan
Det var rena kriget på Fredens skola
Han fick skulden för konflikt på skolan.
Nu sitter vi pa skolan
Föräldrarna stoppade yoga på skolan.
Nya chefer på skolan för Informations- och Kommunikationsteknik
Boende på skolan
But none of these have anything to do with what you're learning at school. That always seems to be i skolan. (Or, vid universitetet...) That's the clearest dividing line I've been able to figure out so far.
Oh, I beg your pardon. I completely misunderstood what you meant. Your question was perfectly clear; I don't know what I was thinking.
It's actually occasionally possible to use på for learning as well. For instance: jag studerar kemi på/vid universitetet.
I've never quite considered this myself, but I'm wondering if "in school" doesn't generally correspond to i skolan, while på skolan is for the more definite sense of it. That way, it doesn't really matter exactly what activity is taking place. At least it is consistent across your examples.