FWIW, getting to middle school a year earlier has been one of the best things about a grade acceleration for my DD, who was 10 for the entirety of her 6th grade year. The larger student body, increased freedom, larger number of teachers, ability to chose electives, ability grouping, and increased executive function requirements that came with middle school made her a much happier 6th grader than she was a 5th grader.

Seventh has been better than 6th, so far.