~10-13 mostly comprises the junior high range. By the time the kids are 14, they're plenty old enough to benefit from a "college-prep" educational approach. Sure, some PhDs will be better, others will be worse. But you solve that by throwing out terrible teachers and rewarding the best ones. There's no guarantee that an Education-credentialed teacher with negligible education in the actual subject they're supposed to teach would be any better.

I'm retired from engineering. I did startups / exited / joined difficult technical domains for the funsies / etc.

I have taught 5 years at a private school. I do not have a teaching credential.

Knowing the stuff you're teaching is the easiest part. And I say that despite teaching in an environment with far better behavior, student buy-in, family support, and academic accomplishment than most places.

I thought that when I launched a student team doing spacecraft design (selected for orbital flight on the basis of the quality of their mission, btw, not their age) that the hard part would be teaching kids about power budgets, radiation aging, and the thermal environment.

Turns out the hard part is helping them figure out how to navigate the social dynamics of talking to each other, organizing their work, realizing what other people know, and coping emotionally with setbacks. Kids will teach themselves the stuff if you have buy-in and the culture in the room is right.