I am going to refresh this thread by reposting much of what I said in post #47.
In post #47 I mentioned how it was it was pointed out, on this forum, that a main difference between an A and a belt in the martial arts such as black belt, aside from the A being applied to academics and the black belt being used martial arts, is that an A is a one time performance, its a mark of performance on a test a student takes. Lets say a student takes a math test and gets an A, that A is just for that one test and so it only measures the student's performance in that one test. A belt of rank such as a black belt, on the other hand, is a result of accumulated knowledge and skill over years of hard training, it is not based on a student's performance in one test the way an A is.
Therefore comparing a belt to a grade a student gets on one test is probably not the best comparison and a better comparison would be to compare a belt to the grade a student gets for an entire class. In academic school, at the end of the year you get a grade for each class based on your average performance in the class. All the tests and grades you got are averaged out for your overall grade. So instead of comparing a belt to an A that a student gets on a math test it would be better to compare it to the grade the student gets in his math class at the end of the year. A student who gets an A in a math class as an end of the year grade that measures their overall performance in the class would work better as an academic equivalent to a black belt than an A in just one test. So that's how they're similar.