I came here expecting a list of ways to piss people off in school.
So far no one's given any good class trolling techniques
If you're looking for pranks, I can think of several, but the OP generally gave an impression of looking for something on roughly the level of fart jokes. If you want something a little classier, just off the top of my head:
Standard senior class pranks:
* Used auto tires cost money to be disposed of. If you go to a mechanic that installs tires, very often they're very happy to give the used ones to you. Get a truckload of them and loop them onto the school flagpole. All the way to the top.
* Or, much easier, far more likely to generate a reaction, and more difficult for the janitor to remove: get a nazi flag and duct tape it to the top of the pole.
* On the day of finals, or national testing, bring a blowtorch and weld the doors shut with everyone inside.
* Most school lockers have slots in the doors wide enough to slide paper into. Print out political propaganda, photoshopped pictures of the principal's head on somebody's naked body, etc. and put them in everyone's locker.
Pranks that can be done solo: * Get a laser pointer. Hide it in your hand, and draw smiley faces on the walls while the teacher is at the chalkboard. Everyone will laugh. When the teacher turns around to see why, turn it off. Repeat. Hold it in your holds in front of you close to the edge of your desk so you can push it into your lap and instantly show that your hands are empty.
*
Bang snaps. With practice you can flick them with a finger with enough force to detonate them on a wall.
* Teachers often leave their classes unlocked during lunch. Get an alarm clock and plug it into the outlet underneath their teachers desk. Set it to go off during class. Bonus credit: get enough alarm clocks to put one under every teacher's desk in the building. Get friends to help. Synchronize your watches so you can set them all to go off at the same time.