Why do orphans not like 1st-5th grade teachers?
Because they have a home room.
Listen up, buttercup. See, orphans don't have homes, right? And teachers have a "home room" at school. So the joke is that the orphans are sad because the teachers have a home and they don't. It's dark, but like, you wouldn't get it. You probably still watch Teletubbies and smear food on your face.