ETA: re: "catching up" socially from earlier in this thread: if we had waited for that to happen before letting DS10 advance academically, we'd still be waiting, because he has Asperger's Syndrome. It was much better to make a plan that met his academic needs and kept working on his social needs as we went along, rather than holding him back with peers who had similar social skills to his, because no matter how hard he and we all try, he is going to be asynchronous in this area for the foreseeable future.
And that can be the case for NT kids, too. When DD was in 3rd, I was talking to the mom of a kid I'd pegged as either the youngest in the class or grade-skipped. Nope, oldest in the class, having repeated K to let him catch up socially. He was still way, way asynchronous.
