FWIW I kept fairly extensive records of DS's development when he was younger (was on a mailing list that had a monthly "what are they doing now?" roll call) and with respect to reading, the thing I recorded that has most often seemed significant since was the first time he sat down with a book that I knew he'd never seen before and read it through aloud (he was 2y10m). That seemed like a watershed: I had known before that he could read loads of words, and sound simple things out, and read/"read" his own books that were familiar, but that occasion when he read a whole book in a sitting that wasn't familiar - glad I noted that :-) (It seemed significant to him too, and maybe it's not too far fetched to say that on that occasion he too realised that he could really read: anyway, he gained confidence very fast after that.)
