By proposing a math curriculum that requires teaching all students the same material, regardless of their ability, with the aim of increasing social equality.

I'm OK with that aim; but I know from my own experience that trying to teach calculus to someone that's not ready for it isn't just a waste of effort, it's disastrously counter-productive (I totally fell out of love with maths when I was taught integration, failed to "get" it, and my well-regarded teacher didn't get why I didn't get it).

My understanding is that nowadays in UK state schools, maths is largely student-paced, using worksheets; they've given up on trying to get a whole class of students to all understand the same stuff. That's partly because a set of worksheets is much easier to come by than a good maths teacher, of course.

I'm not a maths teacher, and I don't know enough about the California curriculum arguments to have a view.