Are public school teachers generally worse than private school teachers in the US?
Based on my experience with both, if I had to come down on one side or the other, I would have a hard time deciding.
Public schools teachers are typically better paid with better benefits so there is a natural draw there for top talent. Lots of teachers teach in private schools so they can send their children there tuition free (or at least at a steep discount).
Also, public school teachers have to be certified to teach. Teaching in and of itself is a real skill. Private school teachers do not have to be certified or trained to teach. We had this very issue with my son's high school world history teacher at a private school. Masters in history but no teaching credentials and only one or two years in the classroom at a different school. It was a disaster. In fact, the department head had to sit in on her class to observe her teaching. As anyone in academia can tell you, if this occurs (outside of student teaching) it's a serious problem. On the other hand, his English teacher was one of the best he's ever had.
Private school teachers also have the advantage of a small school environment and students from high income families. How much of the results are from those factors vs. teaching ability? Hard to tell. Perhaps nothing or perhaps everything.
There are great teachers in both public and private schools. I teach in a public school, but I sent my own sons to a private school for religious reasons. There were mediocre teachers at that private school and I have seen mediocre teachers in schools I have taught. Most teachers, be they affiliated with public or private schools, genuinely want the very best for their students and will go to great lengths to help them achieve their goals. Public school teachers, especially those in urban schools, often have a lot more tools in their tool kit in order to deal with some pretty extreme behaviors.
Generally the contrary. Public school teachers have more qualifications and training than private school teachers. Most Public School teachers have to have a substantial amount of post-secondary education and training, including some kind of hands-on. Private school teachers do not have to have any of that. They also usually are paid less.
The quality of a teacher has far less to do with whether they teach in private or public schools. Rather, it has to do with how they are equipped to do their job, how valued they feel by their administration and finally the passion they feel for their job and their students.
Worse at what? Teaching? Public school teachers in my state are required to have a teaching certificate and a master's degree. Private school teachers don't even have to have a degree in what they're teaching and can remain with a bachelor's degree. You do the math.
Public school teachers are better than private school teachers. Public school teachers have to be licensed by the State. They need to have teaching qualifications and must have at least an undergraduate college degree. Private school teachers do not need to have any qualifications.