This is a good activity for students to practice something without you having to grade a bunch of papers.
Each student gets a card and they have to complete whatever task/problem you give them. Once they have it complete, they raise their hand to have it checked by the teacher. Once everyone has it right, they are the master of their card. You then start the activity.
I set my desks up so students are facing each other. You set students across from each other. They then switch cards and perform the problem. Once they are finished, they ask their partner if their answer is correct since they already have the correct answer. If it is, they switch back. If not, their partner is responsible for helping them arrive at the correct answer.
Once all partners are correct, you then choose which partner will rotate. One thing that I do to make this easier is select two different colors of cards to distribute. Then I just pick a color and that partner will be the rotating one. You continue to do this until you either run out of time or they get back to where they started. This is great for several reasons:
1. It promotes collaborative learning in your class
2. All students have experienced success
3. You don't have to continuously check answers and answer questions
4. Students are responsible for their own understanding
Here are some pictures of my class doing this.