Good luck to you, I hope this placement is as successful as it sounds!
Other than your son being young-for-grade, this dilemma sounds extremely familiar. I definitely have a thread in this forum about figuring out my son's math placement as he entered middle school.
In the end it turns out that our school, while small, has an honors track for middle school, and they readily offered it to both my children. This put them in honors prealgebra for sixth and honors Alg I for high school credit, with a middle school teacher, in seventh. They weren't the only ones in their classes with that arrangement either. In fact I would almost go so far as to say that, if you are "school shopping," that a school that doesn't offer Algebra for eighth graders at all, might not be as good a fit as it seems otherwise?
And I'll also add the caveat that this level of SSA is still not an opportunity, at least for my children, to learn study skills. My 9th grader (who has since accelerated once more and now in Precalculus) was just lamenting about this recently. He longs to know what it would be like to have to study, LOL.
I guess I'd also add that if there's any chance that your son will be interested in competitive math, or a problem-solving career path, or certainly if he'd be the type to consider advanced mathematics in college, then that might raise the merits of AOPS as a flipped classroom scenario. This is actually what we did in 8th grade for Geometry. We started the year fully remote, so we just homeschooled with AOPS. When they went back to in-person, he took a study hall period to sit and do work that I assigned. So, I think that after that experience, I'd advise that prior exposure to AOPS at the Alg or even pre-Alg level, and maybe also having actual live AOPS instructors (instead of a mom who winged it with lesson prep the day before, LOL), would have made it even more successful. Just a thought.
