Its child dependent. ACS makes some good points.
It really comes down to the rate at which someone learns. If a child is going through a year's worth of learning in a month ( I could read most textbooks in a night), then how much value will be that education be if they spend 90% to 95% of their time twiddling their thumbs?
I was happiest when I was radically accelerated, when it did occur. Looking back, my education from 5th grade to 11th grade was a time of extreme boredom and great isolation. I filled it up by reading heavily and my own interests, and I learned very little during that time period from the school system.
Once I was put in AP-level classes, it was finally interesting, but not a challenge. I wasted 75% of my day instead of 95%. IMHO, an accelerated curriculum at a 6:1 ration through 8th grade material and then a 4:1 ratio to HS vs the normal pace would have been perfect. It would have been fast, but would have given me time to indulge in other things as well.
Having said this, I do know of MG kids who are with age-peers at local private schools that have highly intelligent student bodies. The one other PG adult I know, who went to the same school as the kids I know, was radically accelerated by 4 grades and then stayed with that class to graduate at age 14.
