um.. that is exactly how the system works and has always worked.
Kids have always had the ability to skip grades if they were ahead of their peers and had mastered the subject matter.
I skipped a grade when I was in school and I know many people who skipped several grades, it’s fairly common.
Not necessarily.
I have friends and relatives who'd love to have their kids skip a grade or two because they could academically, but the big issue is the social one. The kids would be with (gasp) kids who are not their *peers*.
The schools are very resistant to accelerating kids not only for that reason, but also because they don't want to make the kids who aren't so gifted to feel bad (poor babies).
Maybe it used to be fairly common.....
Um...no it doesn’t and no it hasn’t. In some places and times, yes, but generally not even close to being common. For one thing, the system doesn’t want revenue units escaping.