There's always at least one class that never goes by quick enough. Here are some tips to help the class go by faster.

[edit] Steps

Listen carefully to the teacher and follow along with the lesson.
Daydream. Imagine what it'd be like to go out on a date with that hot girl or cute boy next to you. Or how it would be to meet a celebrity.
If you have friends in the class, throw stuff at them. Do this when the teacher's back is turned. Only throw little things, like gum wrappers or little pieces of paper. Or, just for the heck of it, throw stuff at the kid sitting in front of you without them noticing. See how many paper balls you can get stuck in the kid's hair before she notices.
Write a note to your friend. If you have no friends, write a random note to stick in some kid's locker when the class is over.
Write the lyrics to your favorite song or create some new lyrics. This is a good one because it'll look like you're working.
Play MASH, DKMS, or TAPICO by yourself. These are pretty time consuming.
Write up wikihows.
Text message your friends. Make sure to hide your cell phone beneath your desk.
Get a head start on another classes' homework. Try and be discreet though, don't have your protractor and ruler out in your history class.
Play matchmaker and see who would look cute together in your class. Imagine what their babies would look like. This might cause you to burst out laughing though, so be sure to bite your tongue.
Learn to spin a pencil over your thumb. Your friends will be impressed.
Pretend your teacher is giving the class a sex talk with badly chosen metaphors. This works best in science class.

[edit] Tips

Spin your pencil when the teacher isn't looking, but in plain view of a classmate. After awhile, they will probably try to copy you. When they fail their pencil will go flying and it'll either hit the teacher, another student who might yell out in pain, or just fly out of reach of the student. Whatever happens usually the teacher will notice a pencil flying across the room and when she does the thrower will get in trouble.
Always do these when the teacher isn't paying attention to you.
Don't do any of these if you sit in the front row.
Try and pay attention to the class once in a while. You don't want to fail.
Don't always space out during class. After a while your teacher's bound to notice. And your grades will probably show that you haven't been paying attention also.

Not paying attention in class may cause you to fail drastically.
Do these things at your own risk. They might get you into trouble
If you choose to try and spin a pencil or pen around your thumb, remember that you usually drop your pen several times trying to learn. This may make noise causing a distraction to the class.
These things might get you into detention.
Some of these things are known as bullying. Do them at risk of your reputation