// Unfortunately teacher grading and 'mocks' are notoriously wrong.//
This is often cited, and I don't quibble with it per se, but I think there's a basic lack of discussion about *why* they are wrong. With maybe some exceptions, it isn't because teachers are just being nice for no logical reason, or because they are making things up. It's also because exams themselves are a pretty terrible way of assessing how good somebody is at a subject, so predicting the result is not just about how well that student knows their stuff but also about how they'll cope under time pressure -- which, itself, may be due to random factors utterly beyond the teacher's ability to predict or control for. And, even setting aside, the exceptional, what is the "correct" prediction for someone who has produced work graded as BBABBBBCBB in their last ten papers? I'd assume it would be "B", given they hit that grade 8 times out of ten. But the student showed themselves capable, on a good day, of hitting an A, and on a bad day of getting a C. Was the exam sat on a "good" day or a "bad" one? The teacher can't know. Is it the teacher's "fault" for being optimistic (or pessimistic)?
The idea that reducing a summary of a student's ability to a single letter could ever have been effective is a conceit, one that society really ought to abandon.