Would it be fair to say taht a 500 on the SAT would represent solid Pre-Algebra skills but no mastery/training in Algebra?I think that makes sense. Last year, a 500 was, as you thought, right in the middle at the 47th%-ile. My ds12 took it in January of last year at age 11, halfway through a 6th grade pre-Algebra course. He scored a 590 and we did no prep. I think he easily could have done Algebra last year, but that wasn't an option through our school.
Is your son at a traditional school or home-schooled? For me, I probably wouldn't accelerate much past Algebra in 5th or 6th, simply because there wouldn't be a lot of options where we live and I wouldn't really know at that age whether my child had enough of an interest to really want to do that kind of high-level math later on (but we're more laid-back than many parents of gifted, I think). Our younger son had a principal more open to acceleration and he is on track to do Alg in 6th, which will put him at Calculus in 10th. I figure if he does Calc III and AP Stats in HS, that will be more than enough. If he wants to major in math or engineering, he'll probably want to take anything beyond that at his college. I also want my kids to have "the college experience" - older dd is graduating in three years from college without much effort at all due to lots of AP, and honestly, she's a little disappointed (and being young to begin with, she's had a few age challenges when looking for work and/or internships). Anyway, I know that my view is WAY down the road and you're probably not even thinking about those things, which I completely understand. However, having two older ones now (dd21 has graduated and is working as a biochemist, dd19 is a senior in college), I do tend to take the long view.
However, all that said, if your ds is dying to advance in math and is really motivated and excited, I certainly wouldn't hold him back.
