Like most things, I think this depends on the child. IME, some kids will find a "home" in an HG school, but for various reasons, others won't find the peer group a better fit.
Pros:
1) Kids learn from one another at high levels and smart kids may teach each other a great deal.
2) Work is generally more appropriate, even if not really appropriate.
3) Quirky kids may be more accepting of quirky kids which may help social acceptance of a quirky kid.
4) Enrichment may go farther and be worth more than a typical classroom.
5) Interests are more likely to be shared with a group so a kid reading HP at 6 will other kids doing the same and can discuss interests.
6) Extracurricular activities reflect the peer group and will likely include earlier science fair, math olympiad, chess, scholastic bowl, etc.
Cons:
1) There aren't "herds" of these kids anywhere and an outlier may still be an outlier and still bored.
2) HG programs are taught by elementary teachers. I haven't met one willing to learn enough geometry or algebra or calculus to teach it to a younger elementary child.
3) Acceleration and enrichment and an HG environment doesn't fix the pacing, pacing, pacing issue.
4) Many behavior issues are often attributed to GT issues and a concentration of those kids can have a lot of behavior issues.
5) Schools have a vested interest in preventing real acceleration with the "what will happen next year?" question. Unless teachers are willing to allow a kid to progress, it's still lock-step education with more advanced peers and a more advanced curriculum.
6) Many teachers confuse more appropriate work with more work, so a kid may have much more homework at a young age in order to reach his/her mythical potential.
7) Having a GT or HG program doesn't make a school district any less rigid, bound to procedures, or inclined to make exceptions for exceptions. A flexible, reasonable HG program would be ideal, but I've never seen one.
8) What an HG program claims in presentations and what actually happens in the school may be quite different things. I'd seek info from a variety of families with direct experience of the school.
I believe there are wonderful HG programs in public schools. I'm grateful for them, but there are plenty of examples of kids alone in school districts willing to be flexible and develop what will work for a given situation. Those situations may be better than a rigid HG school. I do not believe that having HG peers solves many issues, especially in elementary school.
