They should just do away with grades entirely.
For the student, it would significantly reduce stress, and so if a student was so inclined to learn, they would likely learn more/better. For the the non-inclined to learn student, yeah, not good, but then again, the non-inclined-to-learn learner probably is going to do well anyway.
What i do think it would do is cut significantly down on the "i hate school" emotion, and "i hate learning" action. Kids probably would like learning more. And to me, anything you can do to get people to enjoy learning, even just a little bit, is a win.