In our case our child was testing many levels out prior to the beginning of calling anything schooling and that continued through home/unschooling. So, I'm not sure I can really answer the question.
I have heard parents of gifted kids who were removed from school for homeschooling/unschooling, comment with absolute shock how fast their kids started progressing at that point. Part of it was probably that the kids were already past grade level. The other part was once all of the time wasting parts of school (line up, busy work, stuff that was not at the right level, etc.) stuff is removed kids who are engaged can progress very rapidly.
I couldn't have said this better, and I too thought that a few of us had helped answer your question. This is exactly our experience. The large part of why we incorporate "unschooling" into our homeschooling is to try and slow down the speed at which he keeps accelerating every year. Our certified teacher is shocked at how much we accomplish in a homeschool day, even when compared against other HS children. This, and we're not even a family who sits down for hours at end with school. Today, DS has been up and doing other things (grocery shopping, his novel, playing swords in the backyard), and still managed to complete an entire chapter in math, 4 handwriting pages, 2 spelling pages, latin, science, a geography activity, and 20 minutes of EPGY grammar in 2 hours of applied schoolwork. Other than handwriting, it's all 2-4 years ahead of grade level.
Uhhh.,..edited to clarify that "playing swords" means waving his plastic Griffyndor sword around while playing Harry Potter with his 2 year old. Just to be clear that we're not totally insane! LOL!
