In my own experience, it can be a good thing or a bad thing. For me, skipping several grades was a godsend and opened up a world of learning and making my first friends at school (mostly about 5-7 years older than me). I didn't have to work much academically--even after radically accelerating--but, because the cognitive age difference was less, I could finally connect to classmates. I'm an extravert and had been very unsuccessful at making friends in my class before accelerating, and I wound up having awesome friends who included me outside of class and wanted to work with me in class after skipping several grades.
DC21 would not have been able to do that. Intellectually, he was several years ahead. Academically, he was about a year or two ahead. Socially, he struggled with other children due to severe 2E issues. Any classroom, especially one including some of the older bullies, was not a great situation, but having him ahead academically gave him more confidence about himself as a whole.
I think each situation necessitates social, academic, and intellectual considerations and input on what has been working and what hasn't been working.
