Funny follow-up story -- 2 months later, with a whole lot of silent patience & tongue-biting on my part and letting his Montessori teachers do their thing at school, DS is now reading books like Mr. Putter and Tabby, and Frog and Toad books, quite easily and often spontaneously. He still likes to just plain guess at a lot of words rather than slowing down to actually figure them out, but he's gotten better, I think.