Yes, schools do not suggest whole-grade acceleration lightly as it results in the child leaving the school one year sooner, which may translate to a loss of funding for that one pupil for that one year. As you mentioned, schools tend to suggest whole-grade acceleration when they have no idea what to do with a child.
THIS.
If the
school is suggesting it, that tends to mean that the child is probably EG/PG.
I know that it was NOT in my best interests to remain with agemates-- I was friendless my last three years in K-12, and this had profound consequences later in life. It was also possible for me to pass all of my AP/college prep coursework while having a 30%+ absenteeism rate, and I was plenty clever enough to make sure that my mom never KNEW that I was skipping school that much. Oh, and when I
was there I wasn't...
all there, if that makes sense. Yeah, being impaired definitely made things better in those (seemingly) remedial classes, that's for sure.
^ just wanted to drive Deacongirl's point home.
I think it is important to understand that not skipping is not a benign choice. There might be good reasons not to skip, but I believe it is crucial to understand how not skipping could cause much more profound problems (crippling perfectionism, imposter syndrome, underachievement than friends driving a year earlier. (My dd will be in this situation next year and she really doesn't care--she is thriving with the skip. While I will not be thrilled for her to go to college a year early she, at 12, is already very excited about the prospect of being done with her masters and working in her chosen field sooner.)
Looking back, (I have a PG DD14) I really don't think that we COULD have kept DD grouped with agemates. Even the most able of them (and they are her friends) tend to be
years away from her academic interests and abilities.
What I will say, though, is that with an accelerated student, it is very important to LET that child be his/her chronological age OUTSIDE of school. Seek out mixed age groups, and let him/her gravitate where s/he will. The upshot is that my DD doesn't regard AGE
as a qualification for friendships.
She's friends with people based upon shared interests and values, and upon the ability to enjoy one another's company.
Most of her classmates are either 18 or will be turning 18 soon. They drive-- though not all of them do. She doesn't. This really doesn't bother her.
The one major issue that has cropped up in having a precocious high school senior is that she probably isn't ready to "go off" to college. She WILL be living with a parent for that transition at 15yo. But we didn't limit her to the local college. She chose that on her own, on the basis of the connections she has in the community, and on the strength of one of the specialty programs at the institution, plus the fact that, for undergrad, it probably isn't THAT critical
where you go. It'll be more or less free for her to attend undergrad. Sensible, right?
Anyway, I think that the only way that we could have avoided skips (we've done 3) is to have homeschooled using something really peculiar. None of us had it in us, honestly. One thing that has made the age less important is that we're with a virtual school-- so DD doesn't spend ALL of her time immersed in an "older" kid-culture.
I agree that for the most part "in-class differentiation" simply doesn't work. I wish that it did.
I am familiar with acceleration up to three grade-levels with additional coursework and projects in areas of interest sought out and successfully completed independently by that child. (An acceleration of 3 grade levels alone did not provide enough intellectual stimulation for that child.)

This is what we've done with our DD. She still finds the graduation requirements for HS to be utterly inane, but she has a LOT of other things in her life that she enjoys.
It makes me very sad that school is generally something that she sees as a pain in the rear end, and something that most frequently
gets in the way of learning, rather than facilitating it...
but she's had a lot of OTHER enriching things in her life, and so we're minimizing the relative impact of that setting.
I don't actually think that most school
can fit PG kids-- not even with regular radical accelerations in the picture. We didn't understand that fully either. What I
wish we had done:
Gr 1-2 DD4-5 (homeschool)
Gr 3 DD6 (virtual school)
Gr4 (GT) DD7
Gr5 (GT) DD8
Gr 6+7 (GT) DD9
(Up to this point, this IS more or less what we did-- we just didn't formalize the last acceleration until the end of 9th grade)
Gr 8 (GT) DD10
Gr 9 + DD11
Gr 10 + dual enrollment DD12
Gr11 + dual enrollment DD13-- graduation.
The last couple of years have been
really bad as far as fit goes. Visiting college campuses (and working on one over the summer in a research internship) has made the ill fit all the more apparent to my DD. She's SO done with this. She
is in dual enrollment and AP course work.
It's not enough. The ONLY classes that even feel "real" to her are things like AP physics and dual enrollment English composition. They aren't hard, either-- just closer to what she needs.
I did
not want to have a 14yo high school graduate. No way. If anyone had asked me 14 years ago what I wanted for my DD, I would have ticked "normal" as the trajectory. I wanted to have my career, have my DD go to a public school like every other kid, etc. That's not the hand that she was dealt, and it's therefore not the one that we got, either.