It depends on the grade though: no degree would probably be fine for a kindergarten teacher, but I'd be a little concerned if a high school math/science teacher had zero post-secondary experience, especially if this were at a school where most students are planning on attending university.

My mother was one of those teachers that had questionable qualifications. This was a problem from time to time as different government edicts and local authority changes made teachers effectively reapply for their jobs.

Eventually she did get a degree, albeit with my father writing up most of the assignments, however, I was underwhelmed by this. I felt that it was quite an indulgence for just a piece of paper.

Subject matter does matter. My mother was teaching art which might as well have been craft. What she brought to the class was experience, experience in crafts and experience existing as a money-making artist. She also knew a few people.

Few in academia could match her skill set and there were no complaints. It didn't matter that she was practically illiterate when it came to writing.

Fwiw, in 1900 my grandfather taught school in Washington State. He was 16 years old.

I don't know how good he was, just saying it wasn't so long ago.