I quickly caught onto how to do it but still felt it was a waste of time. I would use words say what the student was really doing that our director wouldn't know, and odds are the parents too. Sometimes I would slip in the plain truth and see if it got past the director.
At one hole I worked at we weren't allowed to send any mark home that was below 70%. So you would have siblings going home with different size envelopes. The good one would have a thick envelope of tests and assignments all graded. The bad one would have an almost empty envelope. The parents weren't amused and the director would of course blame it on the foreign teacher not giving assignments or tests.
The last hagwon I worked at was great. We were actually allowed to say the truth in report cards. In one case we were painfully honest and it worked. For whatever reason within 2 weeks of getting the report card the student changed and became a good student. Unfortunately those days are done. I am at one that wants you to sugar coat or lie. What the kimchi? Why get worked up. Just play the game.