First, I would eliminate letter grades altogether. In a system based on mastery learning, there is no need and no place for them. Students advance only when they demonstrate clear proficiency with a concept, as measured either by the ten-in-a-row heuristic or some future refinement of it. Since no one is pushed ahead (or left behind) until proficiency is reached, the only possible grade would be an A. To paraphrase Garrison Keillor, all the kids would be way above average, so grades would be pointless.
