Using a student document as the answer key

When we do worksheets on the computer, I like to tell the students that we will use one of theirs as the answer key. They tend to really try to be that first person to get it done and all correct.   When all are done, we go over it as a class and project it on the screen.  If the "key" person makes a mistake, I fix it as a teacher and make it sound like it was no big deal to make that mistake.  Everyone else has to fix theirs as we go over it, but the key person does not have to, since I am doing it on the screen for them.  Works well in Accounting and other classes.