A really good one is to get some tins of tuna, or some other fish, find yourself an air vent in some of the more popular rooms, open it up, and stick the opened fish in there!
Takes ages before the smell comes through, and by that time, they don't know what hit 'em!
It's brilliant!
It works especially well if your muck-up day is just before the break. So the class rooms are locked up over the hollidays, and then everyone but you gets to go back to a nice stinky classroom
Another good one is to go get yourself some gnomes ( by any means necessary
), get some super-strength, quick-drying cement glue, and the night before, glue the things onto the top of a wall at the front of the school.
The one we did it to was we have a fence all the way around, and then where the gates are for the car-park right at the front there's brick pillars, and a short stretch of brick wall with the school logo on it.
It worked a treat, and they even had to break some of the gnomes to get 'em off in the morning
Ahhh, good times!
Anyway, as you've probably guessed, I don't go to school anymore... Now I'm a poor Uni student!
Jess.
[EDIT]
Sorry for those spelling mistakes... my brain's fried from doing assignments all day
[/EDIT]