In my computer classes I have two plastic cups on each computer -- one red and the other blue. The two cups sit upside down, one inside the other. When the blue cup is on top it means 'Everything is Cool.' When students have questions they quietly reach up and put the red cup on top of the blue cup. That means they need my help. They can continue to work and figure out the problem. The students do not need to keep their hand in the air or call my name. It works like a charm. When I start the year, I am very strict about not answering questions from students who don't use the cup. In about a week they are all used to using the cups and like it. It is also a conversation piece at conference time when the parents ask 'What are the cups for?'