My high school had one teacher capable of teaching calculus. His seniority allowed him to fob it off on someone who could not. She left the profession entirely a few years after I graduated.

Of course, one may learn calculus from a book, which was what many of us did in that class.

This is a big problem imo. In my experience teaching high school, a lot of elementary school teachers struggle with basic math... And that's where the problems arise that we have to try to fix later on.