My personal miracle is my English Language GCSE exam, both papers. Predicted a C, which I was not particularly impressed with, as I needed at least a B to do Medicine, which is what I wanted to do, and so I convinced him to put me in the higher tier. My coursework was allright, so I was quite sure of a B, even if I did mess up the paper. I thought that I'd done fantastically well in the mocks, but turns out that it was a foundation paper... Anyway, in the end, not only did I get an A*, but it was the highest A* they'd ever got, and I got 80/80 and 76/80 in the two papers. One-nil to me I believe!
This has nothing to do with revising however. They were just lucky papers - can't remember what paper 1 was, but paper 2 was writing a book review (I'd just finished a book the night before) and writing a letter to the council complaining about speeding (which I've already done in real life). So that's my personal exam miracle!