"My third grade class all got perfect scores on the standardized test. Yes, I did have them each copy my correct answers, but I don't volunteer that information because it's much better for me if people believe I'm a great teacher."
"But that's cheating!"
"No it's not. What were the kids supposed to do when I gave them all the answers? Not use them?"
Is your primary goal to punish/incentivise the teacher, or to accurately determine how smart the children are?
If the latter, you would ignore the 'cheated' answers and judge them on everything else; you wouldn't mark the 'cheated' answers as incorrect.