NEVER try to push more advanced math than your child can handle. The normal sequence for HS math is for freshmen to take algebra one. My son’s district found that even some who had done 8th grade algebra (one year ahead of the norm) were best off repeating the course as HS freshmen. It is best to get a solid foundation, not attempting any shortcuts.
Is your son ready for algebra 1? Needing extra help in his math now may mean he should still be in a prealgebra class- but it doesn’t seem as though your district offers that.
The regular sequence for HS would likely be algebra 1, geometry(trig), algebra 2, perhaps advanced math as a senior if a student really wants it. Some students may benefit from more prealgebra before starting the algebra 1 class. This would still get one through algebra 2 if desired.
Mom- will your son still need special ed services in HS? If he is eligible for them take advantage of what your HS offers. It may be that your son is unable to do math as well as most students. It is better to meet his needs than to try to fit him into regular classes. I know of a girl, now grown, who slipped through the cracks because of doing mainstream math and never could learn it like she might have if they had identified her special need in this. The fact that the school is currently helping your son means he should continue to get the help he needs to learn what is useful for adults. Sometimes extra help during the growing years makes a huge difference- consider the various reading problems. Math learning differences may not be as recognized.
Finally- you need that discussion with his guidance counselor and perhaps teachers involved in his math class. They know him like we cannot and they know their system.