We've had the same experience w/ dd9 this year. We planned to pull her to homeschool and told the school as much. The GT coordinator went way out of her way to make things work better for dd including subject accelerating her in math and offering to let her work on EPGY in school in lieu of the curriculum if that didn't work.
At this point, we've seen the following:
MAPS test scores, which have been wildly erratic (ranging from the 50s to the upper 80s to mid 90s depending on the subject) have both gone way up. Her reading MAPS was at the 57th percentile at the end of last year. They just retested and she's now at the 94th. Reading is not her strength.
Her social group has completely changed. She had been hanging out with kids who were a bit of struggling students some of whom resented dd being in accelerated literacy last year. She was rather lonely and lacked rapport with anyone. She has a totally different group of friends and seems much happier.
Her grammar and speech have improved dramatically. I had long felt that she was intentionally dumbing down to fit in. I came out of a shop w/ dd12 (just turned!) the other day and dh said to me, "[dd9] just said 'whereas' and used it in context!" Her vocabulary has twice come out on the WISC in the 99th+ so we assume that it is there, but it is nice to see her speech not being limited to words and patterns that she thinks look "normal."
I'm glad that a few of us are having the same experience

!