Grades and exams don't actually tell how well a person would do later in life. Especially in many US schools, since most of the contents for exams are just memorized and then later forgotten. Subjects like biology, math, etc. shouldn't be memorized but understood why it is that way, not because someone said so. Also grades usually discourage farther learning for many, making them think they're simply not good enough, and exams cause unnecessary stress. If the way things are taught were to change then grades could become more affective at determining students who are motivated to learns and understand and those that need to try harder.