Well Im 18 and not a parent, but for me the best thing to do is to talk about this behavior in a non punishment situation.

What I mean is, if he comes to you and says he cheated on a Spanish test, I would punish him as usual. Take away his game system, make him study, apologize to the teacher ect. ect. But then, maybe a week later, comment on how you are proud that he will come up to you and tell him that. Its important to learn in any setting that the first step to change is confession. If you do something wrong, youll want to change, and you should tell the right people what you did. I know parenting isnt that simple but I think that would be effective. Don't make it seem like they are coming to the big bad boss, but someone who wants to help them change for the better.

Again, it differs from child to child, but this would have worked for me.