Have you read Richard Ruscyk's article on the Calculus Trap? https://artofproblemsolving.com/articles/calculus-trap

Or his talk about the pitfalls of the standard curriculum for math-talented kids?
https://mathprize.atfoundation.org/...ntation_at_Math_Prize_for_Girls_2009.pdf

If you have a kiddo who already thrives on the AOPS approach of engaging a mathematical mindset and developing a problem-solving skillset, then radical SSA to a middle school algebra class sounds like a wrong turn, in my humble opinion. Not that I don't have a lot of sympathy for the dilemma of having the student spend useless class time and then have to carve additional learning time out of their free hours to make up the difference. In my own child's case, I'm working to make the elementary school hours more interesting. It's certainly not easy to have a little person who's so far outside the typical mold of what the elementary school is capable of working with. :\

Good luck. Oh, and I would leave the Saxon placement test out of the conversation. I don't think it's terribly relevant.