Student work in partners (you can divide how you best see fit). They identify themselves as either partner A or partner B. They then take turns solving problems. While partner A is working out the problem partner B is checking the work and coaching them along if they need help or make a mistake. When complete they trade the paper and in doing so trade tasks, with partner B now solving the problem and partner A coaching and checking the work.
Partners work well if you have one who is just a bit higher than the other but not way above the others level. Not your highest student with the lowest student, but instead a high with high middle and low with low middle. You know your students best of who will work with who and do the activity correctly. This is an excellent cooperative learning and student engagement activity.