There is a survey of early college students summarized here:
early college survey It seems to me that subject acceleration works great for kids who do not need radical acceleration in all subjects. If a child is well-served with most subjects and needs extra challenge in math, it makes sense to just accelerate the math. If the child needs to skip several grades in every subject including writing, literacy, social studies, science, and math, then subject acceleration has serious limitations and cannot hope to meet the needs of the child.
I suspect there are few parents who look at their 5 or 6 yo and plan for early college at 10. I think most parents who end up with children in early college or doing very radical acceleration in all subjects make that choice when their children are 10, ready for college, and miserable doing anything else.
