I think this is one of my favorite idea. Children think of everything as a competition, so by allowing them to see the good behavior of their peers would make them tighten up. I think this idea is a clear Way to let the kids know when to stop and what is going to happen if they don't.
I use this project when I start my multiplication unit to teach repeated addition, groups of, commutative property, and arrays. You could also replace one with a multiplication word problem and picture.