On Windows they are in AppData/Roaming/RenPy/SchoolGame
To get there press Win + R and then type %AppData% and hit Enter. You'll also find saves for other games in that RenPy folder if you ever need them or want to clear them out.
In case you cannot find them, try AppData/Local/RenPy (this depends on your user permissions).
On other platforms I'm not sure where they are stored. :(