Using vocabulary from the week's lesson, I bar the door with my body. No one may enter before the tardy bell unless she/he can define, explain or give an example of what I am asking. If a student gives a correct answer, in s/he goes. Others must wait. Soon there is a group at the door, so if two or three give correct answers at the same time, I let them in. I use this once every seven to 10 days. At first there are unbelieving looks — ‘you have to know something to get in?’ Always there is someone who responds: 'Forget it. I'll just leave.' S/he has always come back. After a few times blocking the door, it is fun to see the happy complaining faces and hear the words, 'Oh no. Here we go again.' When the bell rings, all enter. However, I shout into the room. 'Everybody in here stand up if you want a chance for an extra credit point.' The standing students watch and make sure all the others (who came in at the bell without answering correctly) sit. Next, we decide heads or tails. I flip a coin. If it comes up correct, all the standing students rush to the board and write their names. (I make sure there is plenty of chalk.) I have one of them copy all the names for me. On the next test, all on the list get an extra point. I am always amazed how the chance to get one extra point motivates.