I used this as a review for my students after they had taken a quiz over simplifying expressions. I used the questions they missed the most and made a matching expressions activity. I also created a second set of "wrong answers" that was made up of their mistakes. The students had to mach the expressions, prove they were equivalent by substituting in a given value, then they had to find the wrong answer and explain why it was wrong. If they finished before time was called there is a matching expressions practice I copied to the back of their answer sheet.