>In an ideal world, every student can be accommodated in the learning ecosystem[...]We would also pace what they're being taught to their competencies and give each student personalized learning and testing material[...]But we are nowhere near being able to do that

I only did up to my first year of high school in the US but there is something like this with AP classes. This is especially prevalent in Math, where the year in which people would start Algebra would vary from 6th grade to 9th grade. You could be paced based off of your level.

I remember moving to France after 9th grade and realising that I already knew basically everything that would be taught to me for the rest of high school in Math, because I was able to have such a head-start thanks to my pre-AP Math classes.

I think that shows that the American HS system is in fact well adapted to fast learners, as well as accommodating to slower people (the bar could be set pretty low for the baseline classes because the strongest students were in different classes).

A corollary to this is that the standardised testing was a joke to the set of students who were in the advanced classes. The biggest waste of time ever.

I only experienced Northern Texas' version of this, and from what I heard my understanding is that most school districts in the US could not afford to run programs like this. Thinking back on it, I'm pretty sure Texas has a really good educational system (the results compared to other states are really pretty good considering that Texas is the 4th poorest state in the union).