So, instead of redos, I let students correct their tests/quizzes. I do have very strict requirements, though. 1. The corrections must be on a separate sheet of paper. 2. The new answer must be right (obviously). 3. They must EXPLAIN why the new answer is right or what they did wrong the first time around. If they meet those three expectations, they can get half credit back. The half credit makes it worthwhile for them to fix their answers, but also doesn't just hand them an A either.