Consider the "teaching experience" of a retired, Ph.D. chemical engineer, who, by law, is deemed incompetent to teach in the public schools.
He's got 20 years experience as a student in a classroom. As a grad student, he most likely has at least four years experience teaching undergraduate students in basic college chemistry, organic chemistry, and quantitative analysis.
As head of a commercial lab for, say, ten years, he's had to keep up with professional publications and teach the newer techniques to his subordinates.
It is incredible to believe he can't muddle through high school chemistry (or, for that matter physics, algebra, and other math courses).