We've never had any problems with DS12's grade skips -- everybody knows him, and they know how he is, so it's been a non-event all the way around. Fortunately he's in e-school at home now, so the fact that he's in high school at 12 (turning 13 in a couple of weeks) isn't as noticeable as far as the puberty thing goes. He is doing cross-country for the local high school, and of course woefully behind the bigger kids even though he can run the 5k without any walking or stopping -- his legs just aren't as long as the others' are. But still, they know him. It may get interesting when he gets to a meet.
To answer the question, I'd endorse the other opinions here -- foist it off as a school decision as much as possible, and you should be good.
