momm2boyz, you might try a site search of math curricula and math acceleration/trajectory in particular. That's a question that is discussed fairly regularly here.
I'll also add that in my own admittedly brief experience with Saxon's pedagogy/approach, it was pretty much anathema to my HG+ DD's way of doing things. LOADS of repetition and drill, and very little concept exploration.
While the school may tout the rigor associated, that is not the same thing as saying that such a curriculum is a good fit for most HG+ students.
You'll probably find a lot of different opinions here re: the "right" path forward in terms of math acceleration. Personally, unless your DS is already in middle school or showing a need for extreme acceleration, I'd pick whatever seems to offer the best fit
overall rather than what seems more "rigorous" from the perspective of not yet being enrolled.
Much depends on the relative strengths/interests of your child, too. There are many other academic subjects besides math, after all. Neglecting those does not seem like a good trade just to get in-house math instruction two years beyond the other option.
What
would a child beyond Alg1 do at the other school? Does the school have a policy about that? I'd ask.
