...have you a common room for year 12's at school? Something i've heard about to trash it for next year's lot, is hide raw fish around the place. If you have suspended ceiling tiles, then hide the odd whole makrel above them. Within a few hours, the place will stink.
For a wider area affect, look into emptying a can of tuna in brine water into the air conditioning/ventilation system of the school.
...unscrew assorted chair legs around the school, so that when people sit on them the chairs collapse.
...Other things to put in exhaust pipes for cars include eggs (which should fire out th eback) and, if you are in a particularly vengful mood, use pollyfiller to expand in the exhaust pipe, and blow the engine.
...one of my most entertaining (yet childish) games at school, is, for when someone leaves the class for a short period of time, to turn upside down everything on their desk: books, pencil case, chair, computer keyboard and mouse.
This could easily be transformed to a larger scale. With a small group of friends, pick a classroom, then turn over everything you can. Chairs, desks, tables, even filling cabinates and shelves if you can. The beauty of this, is that you leave it as neat as you found it. Its not about destruction, its about confusion.
