> The system is full up at the moment and you can't really add anything without removing some things.

Middle school seems rather un-full to me. Right now students start learning about fractions in 4th grade. They don't move on to algebra until 9th grade. What is there in the middle? Not much, in my experience.

Maybe instead of having a giant no-math gap during middle school, they could move everything down and free up some space later on.

I doubt it. Local math programs tried to jam those things down sooner, but it doesn't do much good and may do harm. While I understand Piaget is not necessarily the last word in human development, using his terminology, real mathematical education can't really proceed until the formal operational stage is attained. Prior to that all you can really expect is extremely concrete things (in the aptly-named concrete operational stage) like arithmetic. Only single-digit percentages can handle simply moving that stuff earlier into the curriculum. The local conversation on that is distorted by HN having a lot of those single-digit percentages in question, but it's not the normal case.

While I didn't lay it out in my curriculum discussion, I also extremely, extremely strongly support using computers to provide personalized curricula to students designed to probe them for when they are ready to start more advanced math, leading to the complete destruction of the unbelievable awful cohort system in use today, and giving those single-digit percentages the ability to proceed onwards at their own pace, however much faster or slower it may be than anyone else's. But if my curriculum is goring a sacred cow, this idea is goring an entire herd of them at once. The field of education's resistance to computerization has been incredibly effective, to their personal benefit but to all our children's detriment.

Where the heck are they teaching algebra in 9th grade? Here in California that's 6th-7th grade curriculum.

Huh, Australia had (many years ago when I did it) algebra in year 7, and if you were in any kind of accelerated/gifted-and-talented class you'd see it even earlier.