My son took his A levels last year where his predictions, based on his teacher's assessment and mocks, were 3 A*'s and an A. In the final exams, he only got 2 A*, an A and a B. To me, they were still excellent grades but he was gutted. All the way through his education he was encouraged to do his best, particularly for mocks because you never know when you are going to have to rely on them if you miss your finals. He feels very slightly cheated that this year he could have probably have had the predicted grades on his certificate.
Meanwhile, his very last minute merchant, highly intelligent friend is really worried. His mock exams were very poor because he was relying on his finals to excel as he had always done in the past.
There is a very big lesson to learn here and maybe exams at the end of the first year of A levels would have worked better here.