The activity is called Solve 'N Switch, and it is done in partners. Each pair of students is given a stack of task cards (I gave each of my students 8). Each partner takes a card and solves it. Then, they switch cards and solve again. Once both students have done the same two cards, they share their answer and decide whether they agree on the answer or not If the answers didn't match, the students used a dry erase board to walk through the problem together. They repeat the process 4 times (for a total of 8 cards). It is fabulous, meaningful practice, and they are working together while engaged in math conversations! What else could you ask for?
I loved this format because it's so easy to differentiate! In this case, I chose to partner a strong student with a struggling student so that the strong student could help explain errors and processes. In other instances, I might choose to put similarly achieving students together and give them a different set of task cards based on where they are in their understanding of a concept. Perhaps some of the students could be working on two digit divisors while the others are still working on mastering those one digit divisors.
Here is an example of the pages they turned in when they were complete. I was able to take a quick glance over them to see how each student did (in addition to my roaming the classroom as they were working). You'll notice the student on the left circled the check marks for each problem. He got them all correct. The student on the right, however, missed the second problem he did, so he put a slash through the check mark.
You can download a free set of instructions and the recording sheets you see above at Laura Candler's TpT store HERE. While you're there, be sure to take a look around. She has TONS of freebies and other great ideas for cooperative learning.