Tigerle points out what I was thinking as I thought about your post this morning, Cola.
That is, acceleration is generally not a good solution for HG/HG+ students when used as a SOLE means of accommodation or differentiation.
The reason is that using multiple modes of accommodation simultaneously is often a better way of getting a truly adequate balance between finding true academic peers, gaining an authentic social experience with a peer group, etc.
So sure, a PG student at 7yo might be academically best off if placed with 7th or 8th grade cohort, but socially? Not-so-much-- this is probably putting it mildly, come to think of it.
So the other strategies are also important when you're talking about higher LOG:
a. Acceleration, sure (probably unavoidable, but ideally just a year or two)
b. compacting/telescoping
c. deeper/richer/differentiated work/assignments
d. enrichment outside of regular curricular offerings
For example; my DD COMPACTED K through 5 into just about 3 years, then was tracked into the "gt" course offerings in middle school, which included literature electives, math acceleration and higher level instruction/assessments, etc. etc. She was also just 9 years old and in 7th grade-- so accelerated 2y (or was it 3 already? I forget). Her peers were high-achievers and MG kids 2-4y older than she was. This was a more or less adequate peer group until she was about 12-13 and in AP high school coursework, and then she started to outstrip them again, at which point we encouraged extracurriculars to take up the slack, because we didn't want to accelerate her any further due to the age disparity and her "under construction" status with executive function. We spent some of that extra energy hot-housing executive skills in the 3y run-up to college.
I still think that was a reasonably good series of compromises, if imperfect. Perfect didn't exist as an option for her.
