I basically broke the kids up into groups of 4 (I had my classroom set up that way for another activity in Trig class - Add Em Up by Function of Time [Exponential/Log Equations Version], which of course the kids loved as well). In each group, I had a Jack-O-Lantern filled with Tricks (Incorrectly solved problems) and Treats (Correct problems, which I explained are treats to a teacher because there is less for us to fix... they soon realized this to be true).
As Simplifying Radicals said, basically it awesome to hear the kids talking and trying to find the error. The best part, that I added, was having the kids come up with questions they could ask this student. Because of course, we had to have the conversation that you can't just write, "you're dumb" on this person's test.
If you can't see it in the back, I have my Masterpiece Window with names in Window marker! They love it :)