How do you look a kid with a 4.0 and say, "I think you need to work harder!"?
Perhaps you're looking at this the wrong way. Maybe he needs to work
better.
If he understands everything so well, why is he getting Cs on quizzes and tests? And why do his As on his homework result from doing the assignments but not necessarily getting the answers right? (This question may not be a simple one.)
What do you know about the quality of teaching and the quality of his textbook? Have you looked closely at his book? Is it a classical book (e.g. author = Richard Brown, but there are others), where each section has a lot of explanatory text and lots of problems of increasing difficulty? Or is it a new book with constant distractions like lots of
LOUD COLOR GRAPHICS and fluffy examples about Geometry in Real Life! and little text?
What do the homework assignments and exams look like? Do the kids have to write proofs from scratch or fill in blanks in a partially completed proof? Do things like the word "postulate" count for points, as in "Side-Angle-Side" is an incorrect answer but "Side-Angle-Side
postulate" is correct? My very mathy son got a C on an exam last year because of multiple point losses due to this kind of thing. He should have scored 100.
If kids are writing proofs from scratch and the difficulty of problems in each section increases, it sounds to me like your son doesn't understand the material, in spite of what the teacher said (teachers can be wrong). If he's getting a C because "SAS" is wrong and "Side-Angle-Side postulate" is correct, the entire problem is, IMO, moot because he's not being taught real geometry anyway, and learning how to score high on fluff is pointless (this is why my son is homeschooling this year).
A lot of kids end up in remedial math during their first year of college. IMO, part of the problem is that they got As and Bs in marshmallow math courses starting way back in grade school, and reasonably believe that they can do math. Yet colleges are still unforgiving this regard, and I suspect that the students are at a loss to understand how they could bomb a placement test when they did so well for all those years.
