The "what if the kid wants to be a teacher" was not an arbitrary question, but very specific to this thread. Most advanced black belt ranks qualify you as a teacher of the art. There are many reasons to promote a kid to the next grade in school, even if he's behind in reading. He might be good in every other area, or it might be social (i.e. you don't want an 11 year-old 2nd grader to hang out with all the 7 year-olds). The point at which that student will hit a wall is probably college. At that point, there are stricfer entry requirements. It's a lot harder for a C student to get into college than an A student. However, this is a little bit different than martial arts, where you typically stay at the same school. I went to 2 different elementary schools, and then a new middle school, new high school, a college, and a university. Yet, my TKD career from white belt to 3rd dan has all been the same school. I didn't have to apply to a new school after getting my black belt, 2nd dan, 3rd dan, etc. There is no barrier for entry of the application process, other than internal validation in the form of testing. That application process tends to reset progress based rank, and focus instead on your skills and qualifications. And if a school wants their advanced ranks to meet those standards, then at some point they need to simulate that application process.