One benefit to grouping students in homework centers is that it frees up the Classroom Leader to focus on those who need extra help. However, there's a drawback to this strategy.  Namely, one student does all the work while the rest of the group copies their answers. Here are two games designed to check student comprehension.  They both work by breaking the answers down by steps, and are a lot of fun!

Hat Rack

1.  Go around to each group and tell them that you're going to ask them to explain one of their answers.

2.  The students must be able to break down the answer into three steps. 

3.   Ask them to imagine they have three hats, each holding one of the steps; as they answer encourage them to dump out the answer and then hang their hat. For example: "I wrote down 9x9," and then they tip the hat and put it on the rack (younger students can have fun pantomiming the gesture).  "That means that you add 9 to itself 9 times," dump hat #2.  "9, 18, 27, 36, 45, 54, 63, 72, 81!" And there goes #3!  

4.  Try this for different subjects.  Remember the idea is to get students to strategize simple steps that explain how they solved the problem.

Horse

1.  Ask the group to stand up.

2.  Choose an answer.

3.  Ask the first student standing to say the first step for solving the problem; if they can't then they get an "H."

4.  Keep going around until all the steps have been said, or only one student is standing!