I go to a boarding school in England, and traditionally, the oldest grade takes part in 'Fun week' after exams are over. However, last year, some people in my grade helped the older kids too
Some pranks included:
-Bringing live chickens into the dining hall
-Filling a boy's room with balloons from ceiling to floor (He had a phobia of balloons)
-Filling another boy's room with half-full paper cups all across the floor
-'Flatpacking' another boy's room i.e taking out all of the furniture
-Sticking a young boy to a wall with extra-strong tape
-Antiquing, i.e covering people in flour when walking past
And some ideas for this year include swapping everything within two boys' rooms, a massive nerf gun fight, and making our own artificial beach for a hawaiian party!!
But of course, the teachers are not told before hand