Studying the subject academically in any real capacity.
Among current K-12 teachers in the United States, what would you estimate is the median number of academic/research papers related to education or adjacent fields that they have read in the past 24 months?
in the US, every teaching degree requires
"There are thousands of effective teachers without teaching degrees."
I doubt it. And there are countless thousands more that are terrible and whose kids are very behind.
How is this different from "I went to teachers' college so I know how to teach"?
I'd imagine there are approximately zero homeschoolers who are managing a classroom of 20 kids.
The skills, knowledge and behaviors required to obtain and keep a job as a public school teacher are not the same as those required to homeschool your own kids.