Personally, I liked teachers that were enthusiastic about their subject matter more than anything else. Learning how to teach must be important, but someone that has enthusiasm and a skillset could surely pick that up as they go.
1. https://www.mhec.org/sites/default/files/resources/teacherpr...
A 18-year-old has typically spent 20-25% of their waking hours in formal education, depending on what you count. That's a substantial fraction of their life so far. Formal education is particularly important for less fortunate kids who don't learn many useful things from their friends and family. If you want such people to have rights and responsibilities, they must be given a chance to prepare. Otherwise the society will suffer.
Sounds like the early days of Teach For America where enthusiasm will mostly get you between a few days and few years of service.
I think it’s pretty complicated to measure the effect of teachers in lots of context, let alone with respect to educational attainment.
The exception is at the intervention level: Teachers who learned X technique for improving Y skill improved Y skill at a higher occurrence than teachers who did not learn X technique.
Even for interventions you need to develop understanding of childhood/adolescent cognitive and emotional development in order to communicate effectively. Maybe enthusiasm gets you there organically through experience, maybe you quit.
Certainly in an otherwise pristine learning environment, enthusiasm for learning itself is a baseline desirable trait.
My experience is that the people with the best natural teaching ability are not teachers. They end up in random industry jobs because dealing the career ladder of teachers is super unappealing.
In contrast, the teaching profession is full of people who were good students. So requiring more degrees does not do a good job of separating the wheat from the chafe.
In my experience, the best teachers are people in their 50s or 60s who have a ton of diverse experience and still chose to teach. But the median teacher is someone in their 30s who has only ever been a teacher.