Where do I start
The usual mundane putting chalk inside the black board rubber, hiding the waste paper bin in the roof of the classroom (we had a poystyrene roof tiles), drawing a chalk line behind the dangling cord of the overhead projector screen that hangs down in front of the blackboard. But on a different level....
Mixing concentrated sulphuric and hydrochloric acid in a test tube and placing a length of rubber tubing in it then inserting a lighted spint down the middle which explodes and shoots the rubber tubing onto the ceiling where it sticks!
Making Potassium iodide crystals and sprinkling them on the floor so that loud explosions occur when anyone walks on them.
Taking the fuse out of the overhead projector plug so that the teacher thinks the machine is broken and has to go and find another.
Devising a system with farmers children whereby 4 piglets are taken to school marked with the number 1, 2, 3 and 5 and setting them loose.
Setting up a walkie Talkie under the teachers desk and then giving them instructions as they write on the board.
Is this why I didn't take up teaching as a career!!!