Even if there's a good reason that you couldn't study, something you can't and shouldn't ignore for example, you should tell the authority and take the test later on. Even when a later date isn't an option, doing your best is better than the 0 you might get if you get caught and no one will even listen to you after that.
I think this is a really bad sample to the children. Because that will not help you to learn something when you are doing some difficult things. When you start to cheat. You will think "I will do this only one time!I will do harder next time",but next time you will still cheating. So,cheating is really not a good thing! It will forming a vicious circle