Our DD skipped 6th grade and joined middle school in 7th (around here middle schools are 6,7,8). I have often said one of the best things about that skip was giving DD one less year of middle school. Even the school principal, in our acceleration meeting, flat out said, "Middle school sucks, even for non-accelerated kids."
It took our DD a few months to finally get accepted into a group. Until then she kind of toughed it out, mostly hanging out with the kids the guidance office had asked to take her in (in addition to the acceleration, our DD was also new to the district). Now she is a junior in high school and her groups have completely changed since middle school.
Did your DD's acceleration plan include any monitoring and/or follow-up from the school to see how things are going for her? Having the school keeping an eye out for our DD, and getting involved in extra-curriculars (swim, band, jazz band, tennis) help quite a bit.
It was a tough time for my wife and I to see our DD not immediately thriving socially after her second acceleration, but looking back now (~4 years later), we are (and she is) so happy with both the academic and social fit and (other than a little ribbing) most of her friends don't even think about her being younger.
Best of luck,
--S.F.
