I'd also like to point out something that we've found to be more damaging than the more obvious social issues that teachers/administrators tend to think about and caution parents about. My DD found that being with academic "peers" who were 3-7 years older than herself, in a non-differentiated setting, actually made her feel LONELY and ALIEN. MORE lonely and alien than a non-differentiated setting with agemates did. Of course, it wound up (for us, anyway) still being a matter of least-worst placement, but we did shift things into the higher "honors" track as often as we could... which helped, but didn't entirely eliminate the problem.
Why? Well, I don't know for sure, but the explanations that DD has given indicate that she was able to process her differences from agemates as "I'm older in my brain development." Until she encountered those older peers, and then it became painfully obvious that THEY aren't her peers either. Not really. She still has to hide a great deal of her ability on a daily basis for social reasons. Ergo, she is a singularity, belonging nowhere.
This is a powerful reason, IMO, to not place a child into a non-differentiated and multiply accelerated environment. It's neither intellectually nurturing nor socially so, all too often. The only thing that my DD has gotten out of it (again, generalizing) is being treated like everyone's favorite sideshow or a weird kid sister. She puts up with that rather well, but only a fool confuses being treated like a kid sister with genuine friendship. HG+ kids are nobody's fools, generally speaking. This is most painful in early adolescence.
This has been our experience as well. My son is now accelerated two whole grades and it's still not enough. I am currently trying to figure out if he has any real friends in this placement or if they're just politely tolerating him.
