It's possible to undo a skip, but that process doesn't come without pain.
That is true, but neither does lock step schooling come without pain, immense pain for some children. The problem is that there is no problem free approach.
I think that this is an area that is DEEPLY impacted by what AEH says about many of the issues that happen with acceleration stemming from schools not being accustomed to accelerating children.
One of the cases I was most struck by in Miraca Gross's book was of the child who completed yr11 twice and then yr12 twice. Not to hold them back, not because they hadn't done exceptionally well (they had), but because earlier acceleration had bought them TIME. Time which they could use to fully study twice as many subjects at a yr11/12 level as is typically done.
This is a marvelously flexible approach to allowing a child to progress out of primary school as they need to, but not necessarily leave school as fast as they left primary school. It certainly won't work for everyone, but it's a great option. Options like this can ONLY work when a school is incredibly supportive and really embraces the process with teachers and student body.
If they look, talk & walk like, and are otherwise indistinguishable from, older peers at the time acceleration is considered, it’s likely to work out.
This has probably been a significant factor in things going well for our accelerated child. It's not without issues, but no-one thinks things would be better without the skip (and it has been discussed more than once).
She sailed through school and I still remember the high school principal’s shock when, at the end of eighth grade he congratulated us on raising ‘such an incredibly mature 14 year old’, we told him she was 12.
I went to collect my child from a specialist music lesson and both child and teacher regaled me with the teacher's complete inability to hold my child's age in mind (which teacher did know).
Teacher reported how he had said: "Now I know I am being VERY hard on you for a 14 yr old. These are tiny technical details I don't usually get into until much later, but I think you are ready for this."
Child: "But I am not 14..."
Teacher: "Well very hard on you for a 13 yr old! But you can do this!"
Child: "I am 12."
Teacher: "We can still do this!"
This was the most extreme version of this conversation, but we regularly had to correct the age perception. Especially with regard to the emotion of pieces. ("It's very hard for a 14yr old to get the full emotion into the playing of this piece" "Twelve yr old").
Music is an interesting situation, because it is completely acceptable to progress at your natural pace. It is normal for there to be some VERY young participants in our elite national youth orchestra, which is made up mostly of tertiary and final year high school students. And there ARE conversations about sending your 12/14/16/18 yr old off to a (probably interstate) residential music camp where the age bracket is "Under 25". Most people would have to have a good hard think about sending their middle school daughter interstate to a residential opportunity where the majority of the attendees are in the 18-25 bracket (note that 18 is the legal drinking age here too). And that is very reasonable. But the conversations about these issues have a very different tenor to the conversations about school acceleration.
Obviously you could argue that it all boils down to protecting the child. But there doesn't ever seem to be a developmental argument around music opportunities, that your child will somehow fail to develop normally if grouped with older children/youth of equal ability. It's very much a question of "Is it safe?" and my experience is that it is very gendered (families that would send the son but not the daughter for example, music teachers who recommend girls should not be allowed to attend before 18). And you do see tiny little boys crossing the stage with their instruments at times (some who must be older than they look). I am not sure that my thoughts are leading anywhere useful, but it's an interesting contrast to the advice about acceleration in schools, where being a physically more developed girl is an advantage and a small boy is disadvantage!
