If you read my comment slowly, you'll notice that I do not rate teachers in absolute terms, or on a scale at all — I actually hate that (and, yes, I have grave

If you read my comment slowly, you'll notice that I do not rate teachers in absolute terms, or on a scale at all — I actually hate that (and, yes, I have grave concerns with your “2%” or “90%” because of that). What I did write was that some teachers, no matter how great, come with details (unmeasurable in most cases) that are problematic: their accent is the most common one; details that can be easily fixed (ask Pigmalion), but that rely on intelligent feedback. No numbers. I don't like numbers.