An excellent way to engage students in coaching each other is an ask ask trade activity. Here are a set of ask ask trade cards for expanding single brackets:
The idea is that you give pupils a card each which contains a question on one side and the answer on the other. They walk around the room and find another person to form a pair. One student shows the other the question on their card and waits for them to answer it. Then they compare the other student’s answer to that on the back of the card and have a discussion about where they went wrong if they did. The same thing is repeated the other way in the pair. That’s the ask ask done and then they trade by swapping cards. They then go and find someone else to ask ask trade with.
The idea is that knowledge gets passed around the room between all pupils, rather than just sticking within just pairs. You can circulate and give our merits/ credits/ praise to pupils who give the best feedback when their partner got an answer wrong.