Between San Jose and San Francisco, 15%-30% of kids are in private school (it's 30% in SF where the public schools are extra dysfunctional). That's far above the California statewide average of 8% in private school.
Among our peers, somewhere between 1/4 and 1/3 of kids are doing advanced math outside of school, typically either Russian School of Math or Art of Problem Solving. This group only partially overlaps with the private school group. This is happening despite the fact that both public and private school teachers strongly discourage math outside of school!
So by decelerating math in the public school, incentives were created for privileged parents to take matters in their own hands and put their kids into programs that accelerate math education far beyond what public schools used to do. We now have a system that is creating even wider disparities in outcomes. It stands to reason that it's producing far less equitable outcomes, too, given that extremely bright kids who happen to be in lower-resourced schools have fewer opportunities. Universal screening for giftedness, advanced public school math courses, and the SAT -- all avenues for advancement regardless of background -- were all eliminated.