Of course, this means that the College Board, ACT, and (to a lesser extent in the US) IBO have become somewhat national curricular guides, at least for most* high schools trying to get their students into college, due to desire to have students do well on the tests used for college admission and placement. But then that could mean culture wars regarding the content of (for example) AP US history and AP US government.
*Other than perhaps a few academically elite schools that choose to have their own advanced curricula, or which cater to students who want more advanced material than the “normal advanced” college frosh level material, or which are academically specialized niche schools.