Show your thumbs: a quick check for understanding

A quick way, I can check for understanding, is by having the students do thumbs up, thumbs down or sideways to a given student answer.

I will give a practice problem and after the students work it out, I will have student either verbally give the answer or write it on the board. Then I will ask class, if they agree with the answer. I will say on the count of three, give thumbs up if you got the same answer, give thumbs down if you got a different answer, and give thumb sidewise if you got stuck and did not finish the problem.

This gives a quick way to see, if I need to go over the problem again or work out more examples.