Last year D15 and I were discussing an exam that had not gone as well as expected. Somewhat ironically, I pointed out that just because she knew something didn't mean that the teacher KNEW that she knew. And that the point of most of her assignments is to prove that to the teacher, so actually TELLING WHAT SHE KNOWS is good. D looked flummoxed. Somehow in all her years of schooling, she had missed this... She said, "But it feels so stupid to tell the teacher material that THEY ALREADY KNOW". And wouldn't that be boring for them to grade so many assignments on material they already knew??
She did accept this new (to her) viewpoint, and has pretty much played along with it since. Resulting in a definite improvement in her grades

But she itches to work on something her teachers don't know... Just thought you guys would understand this story better than anyone else I know.