Here's one I've made for GCSE Physics:
@k8nowak explains:
Make a worksheet of problems organized in two columns. Column A and column B. The tricky part is the pair of problems in each row has to have the same answer. Obviously some topics are more suited to this than others. (Solving linear systems, easy. SOHCAHTOA, easy. Graphing inequalities, hard.)
Pair up the kids. Decide who is A and who is B. Tell the kids to only do the problems in their column. When done, compare answers to each question number with their partner. And if they don't get the same answer, work together to find the error. That last step is where the magic happens. I know how well I taught the topic by how busy I am while they are row gaming it up.
http://function-of-time.blogspot.com/2009/10/row-game.html