There is a boy in DD's fourth grade class who turned 8 shortly after school started this fall (he was accelerated back in kindergarten or first grade), and I think he has had a lot of problems socially according to his mom. He's probably 1.5 years younger than the other kids, on average. He also dislikes school, presumably because of the social issues. I'm not sure if she regrets accelerating him or not. We accelerated DD one grade but she was close to the cut-off and doesn't stick out as being obviously younger. Before she was accelerated she was a leader in her class and older than the other kids, now she seems average in terms of leadership qualities and how she fits in. I never thought of her as being socially immature, but I think if she was it would be difficult. I don't necessarily buy into the theory that gifted kids will fit right in with the older kids and adapt. I think it depends on the kid and it's an important factor to consider, probably just as important as the academic aspect.