This gets more able pupils to show their working and provokes discussion about different calculation methods.
At the beginning of the lesson, which could be on almost any topic, explain that you will look at the stages in their calculations rather than just the correct answer. For the plenary, I would put up pieces of card numbered 1 to 10 (perhaps corresponding to the numbers of each problem). They mark each other's work and score points if their solution included what is written on the reverse of the card. The cards can be as specific or generic as you like, from "included a labelled diagram" to "y= mx + c"
Frances Watson teaches at Sharnbrook Upper School in Bedfordshire.