This is an activity that I created for my students to find the mistake in rational number problems that have been solved incorrectly. I used common errors when creating this to help them see the mistakes I see when I grade papers.
I had the students work alone to find the errors first, and then share with their groups. If there was a discrepancy, they looked in the answer folder on their tables to see the correct answer. It was terrific to see the discussions that were going on! This really worked well!