The Teeter is a very scary obstacle for most dogs. It's a plank that rests over a swinging base in the middle
The dog has to run up on it from the side that's on the ground, cross over the center point causing it to tip, wait for the other other end to hit the ground, and then exit down the side that's now on the ground (opposite of starting end).
Like the other contact obstacle, the Teeter has a sandpaper-like surface, and also has the yellow contact zone on both ends. The dog has to touch the contact on both ends before entering/exiting the obstacle. The dog must also wait for the exit end to touch the ground at least once before exiting - it's okay to jump off while the teeter bounces back up, but not okay to jump off while it's descending for the first time.
Most dogs are not very fond of falling to the ground together with the board and are often tempted to jump off to the side as they feel the board to begin moving. The banging sound of the board hitting the ground can be scary too.
The preferred performance is for the dog to run well past the center of the board, causing it to tip very quickly, and then exiting off the board. The problem with this though is that it causes the board to move fast and make a lot of noise, which is very scary. Hence, many dogs prefer slowly crawling to just the point where the board will gently slope to the other side, but that's a big waste of time.
The first thing to do when teaching the Teeter is getting the dog used to the bang sound. Usually, you would hold the dog next to the Teeter, and move the board down with your hand, letting them see and hear it. Start off gently, and as the dog gets confident move up to slamming the board down as hard as you can (making sure you don't hit the dog of course). Once the dog gets used to the motion, it's time to get the dog on the board. It's best to start off by holding the Teeter motionless, letting the dog go up towards the high end, and slowly moving the board down as to not scare the dog. Even this exercise can prove to be very scary, but with lots of patience (and yummy treats), the dog should eventually learn to stay on. After that, it's just a matter of getting them to go on their own, letting go of the board earlier and earlier, until you no longer need to hold it at all. Keep in mind that you want the dog to go far up and get the board moving fast. The crawling method is best discouraged as it would be a very hard habit to break in the future.
Another thing to remember is that the bigger (and heavier) the dog is, the faster it will get the Teeter to move. Smaller dogs are at a disadvantage, but at least they tend to be a little braver of going farther up :)