Senior Prank, 2K4
Alright, the idea here is to confuse as many people simultaneously as possible and shut down the upper-school for a few minutes. Each participant will wear a hooded sweatshirt, glasses, and a not yet decided symbol.
I'm going to measure out and make 4 sets of rope/cable harnesses. At one end of each harness will be a handcuff-style lock, and at the other end a 90-degree metal bend that will fit in the crack between the lockers and the wall. At a pre-determined time, 2 (or 4) accomplices, each with a set of harnesses will lock the end of the harness onto a door handle in the upper school, slide the clip into the wall, and then tension the harness. This will be practiced and should take only a few seconds per harness.
Once all the doors are 'locked,' they can only be opened from the outside (the doors open in). At that point we set off the 'alarm.' No, we will not pull the fire alarm that's stupid, unoriginal, and illegal. I will have placed a loud obnoxious alarm of my own in 2 hidden places in each hall, and once all the doors are ready I'll trigger it. Sure should make for some confusion when people try to get out of the rooms :-)