I posted 15 add/subtract fractions with unlike denominator problems all around the room. The students were given this worksheet to fill out. Students were instructed to go to a problems, work it and then come back to me for a conference. I signed it and gave a check (correct) or an x (incorrect). At the end of class students added their checks for bonus points.
This was a great opportunity for me to see where the struggles still were. For the most part the struggle is still remembering to simplify.