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

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.