Sometimes you make it to school in the morning, and you just don't want to be there. I'll be a senior in the fall, so needless to say, over the past eleven years I've gotten pretty creative and tweaked my system until it was flawless. So here it is, the method that never fails...
Best of Luck! This method has sent me home many times, hopefully it will do the same for you.
Step 1: Go to the bathroom.
Like all other good ways to go home, a trip to the bathroom sets the mood. Go to the bathroom, bring your cell phone, sit down on the toilet, and enjoy 7-10 minutes of your favorite game. If you're going to play some games, make sure your game settings are on silent.
If you don't bring your cellphone, just chill in the stall for a while. Or you can make a quick stop by your locker and get your calculator, TI-83/TI-84. I have a bunch of games on mine. Just relax and burn up some time.
Step 2: Head back to class.
Go back to class. With any luck your teacher will be sitting at their desk and not standing there teaching. DON'T SIT DOWN. Go straight to the teacher's desk and say: "Hey, my stomach isn't feeling too hot, may I go to the nurse please?" (Or the office if the nurse isn't there.) Without doubt I always get "Sure Eric, head on down".
Step 3: Talk the talk...
Once you get to the nurse or office, stay confident and serious. Just say you've been to the restroom a few times this morning, and your stomach isn't feeling good. Say you have been making frequent trips to the restroom and want to go home. Something along those lines, just get the idea of mad diarrhea across. Do not tell them you have a stomach ache, if you do they'll just give you some tums and tell you to wait it out. Let it be known that you're about to explode. More than likely they'll tell you to call your Mom, and then you're home free.