This will normally happen once you hit middle school/junior high.
One student pokes his or her head into the classroom sees you at the desk, beside the desk, under the desk, on the desk (ok, hopefully you aren't under or on the desk) instead of their teacher. They ask if you are their substitute teacher (I'm assuming at this point you say that you are or you know you could come up with some hilarious made up story as to whom you are) and they run out of the room to spread the word to all their friends, friends friends, and even their biggest enemy.
Suddenly you became Ms (or Mr) popular.
You are the talk of the hallways.
You are all that.
And a bag of potato chips.
Wondering where I found the cartoon?