This is an incredibly informative and interesting discussion. All the replies have pretty much confirmed what DH and I expected, much to the chagrin of some, I expect! What a strange myth to be perpetuated, really.
I also found the comment about learning/growth being 'exponential vs. linear' both affirming and slightly alarming, lol. Even though it clearly seemed that way, one doesn't necessarily like to assume that their child is going to be THAT far ahead. But in the end, I think the most important thing is to be an advocate for your child, so that he gets the kind of education he needs and deserves.