Well 6 or below is bad for school because they want you to know everything, ideally. I think that's fair. If 50% knowledge of your curriculum was a passing grade that'd be kinda silly.
But school isn't "rating" something either. No point in condensing the scale like that for a rating.
--
I tried to have a fierce rivalry with SuperNiceDog, but he made me look worse than a GameFAQs Contest!