I saw this very clearly when I was in school. Grades don’t reflect your aptitude, intelligence, or understanding of the subject matter. You don’t need to actually learn much useful material to get good grades. (And many of those who learn exceptionally well don’t get good grades.)
via Marco.org – School grades are hopelessly broken. Yet another in the long list of people for whom grades don’t matter and are worthless measures of ability. The larger problem isn’t that grades as they exist are a broken system, but that we don’t have any good concept of something that can scale to deal with millions of students and yet still capture exactly how much knowledge a single student actually captured and is able to apply years later.