My cousin’s class had one of those ceilings where you can lift up a panel and there’s an empty space between the ceiling and the next floor. So one day in Adar they put an open popcorn popper up there, right above the teacher’s desk, and turned it on just before the teacher came in.
I heard a rumor also about a class who brought in a CD player with a CD that said “Help, help” on it and kept repeating it, and then hung a stuffed pair of pants with shoes off the windowsill of a classroom on the nest floor. I don’t know if it really happened but my cousin swears it did.
And of course, there’s the old trick of Saran wrapping the secretary’s desk.