I've written before about how Koreans never wear their shoes inside. They believe that outside shoes can carry diseases, and are terrified of becoming sick. This idea carries over into the schools. Students literally take of their shoes at the door and walk in their socks, carrying their outside shoes up to their classrooms. Outside each classroom are these shoe cubbies (that's a fun word) that house their school slippers.
So, during the school day, the cubbies are filled with their outside shoes...
And after school is out, they are re-filled with their school slippers.