This is an activity that I created for my students to find the mistake in the proportionality problems that were solved incorrectly. I used common errors when creating this to help them see the mistakes commonly made. This would also be a great review activity before the final proportion test. All of my products are common core aligned.
I had the students work alone to solve the problems first, and then share with their groups. If there was any discrepancy, they looked in the answer folder on their tables to see the correct answer. I rotated around monitoring and helping as needed. It was terrific to see the discussions that were going on! This really worked well!