This is a very important distinction to make, however issues with this style of teaching (training rather than deep education) are difficult to see in subjects

This is a very important distinction to make, however issues with this style of teaching (training rather than deep education) are difficult to see in subjects other than mathematics. At a high school level, I doubt any subjects really build on early learnings as much as mathematics. History, biology, and chemistry for example are all easy enough at the US high school level, as little actually builds on top of early concepts. Sure, it helps to have insight into theory behind chemistry, but I can still memorize some elements, molecules, and energy levels of electrons. High school doesn't really go beyond that. Mathematics however, is incredibly abstract, and without a framework of theory to encompass everything, is just a vague sequence of techniques.