However, many of these problems are related, and I do not think we can solve one in isolation. Thus rather than try to say when I think the whole problem of school mathematics has been fixed and is working well, I think it is sufficient to look at one problem there and see when it has been solved. The one which is easiest to look at is the problem students taking calculus have with algebra. Some have tried to attack this problem by redefining calculus, just as they have tried to attack the problem of poor arithmetical skills causing problems in algebra by changing what algebra is. Neither of these will work, and we need to go back to fundamentals and solve these problems directly.
Elementary school is the most important.
While this is not true universally, I am afraid it is an accurate description of far too many classes. Many calculus students have told me that they wish they had studied in high school, but no one else did, so they did not either. Some of this talk is for show, but far too much of it is accurate. When students no longer say this, then significant progress will have been made. This must not only include the mathematics being taught, but mathematics which is taught for the next few years, for how something is taught should partly be determined by the desire to point students in the right direction to learn later material.