My wife (engineer) taught a class called 'Math for Teachers', which was designed to teach elementary school teachers basic math. Not how to teach it, just how to do basic math themselves. A significant number should have failed that class but the administration refused to allow her to fail teachers who were failing for 'reasons'.
Absolutely what I observed as well with SF school teachers. Some were good and knew basic math and basic grade school English but a good number spoke and wrote like dropouts.
Being a teacher is probably the opposite of being a politician.