You can say that when your school can provide 2 or more teachers per class of 20 pupils in high school, but as far as I know, in contrast to the schools where I'm from, in the US that doesn't happen.

With growing class sizes, and less teachers, US schools don't have the resources to focus on individual students' needs. The best they can do is trying to get some students through.

They could adopt the more modern concepts, where small groups of pupils get a task they can't do yet "derive a function", each group gets given some hints in which way to try it (each group in a different one — one going via limits, the next doing it numerically, the next graphically), and then each group presenting their concept to the others, and comparing.

Those, more modern teaching concepts, also allow for good teaching for every student with a low amount of teachers (and teach independent understanding, research, etc), but they're rare in most countries.

The resources allocated to education are not infinite.

They don't need to be infinite; education just needs to be taken more seriously. And the public in general needs to understand that social programs they like need to be funded, and that sometimes means more taxes (education is basically a social program).

The US has a very high wealth per capita - if other countries with similar resources can do it, so can the US.