By the time an ambitious student finishes high school, they will have learned some manipulations in linear algebra and calculus by rote but they won't have any real understanding. If they enter college and study some further mathematics, the first task of their professors will be to undo the damage.

We don't need to teach more, we need to teach better. We should not chase nominal accomplishments such as whether students have "covered" differential equations and discriminants by high school's end. There is already too much of that. The same is even more true for the foundational material taught in middle school. If you skate across the basics in an effort to cover more, earlier, you risk serious damage to the students' development in mathematics and science.

The problem all comes down to 10% curriculum and 90% teachers. Curriculum only seriously concerns me when it overconstrains good teachers and prevents them from doing their job.