Well, there’s something in that. My niece teaches algebra to eighth graders, and barely had enough math courses to qualify as a math teacher. But because she is able to get the least promising eighth graders to learn algebra, she is highly valued by her school and district, and won teacher of the year for her district. I’ve probably forgotten more math than she knows, but I could never get anywhere with those kids.
Very little is needed to teach 8th graders algebra. And I mean little as in don’t clutter the kid’s minds with non-relevant crap. Kids need to master arithmetic before algebra. That’s not a lot of knowledge to master and they have 8 years to do it. It doesn’t take a great deal of knowledge on the part of the teacher either. However, it does take the ability to teach.