Just a couple of thoughts.
It’s not unusual for a school to not allow tests to come home. My D’s wonderful HS school had that policy too.
We pulled our D out of the public school system as well (for all of HS) because of issues with AP/honors offering being eliminate with budget cuts, elimination of arts/music, etc… The school turned itself around but as for your student, it would have been too late for our D for it to make any difference.
We absolutely LOVED her HS but I will caution you that even in the best schools, including in college, there are going to be horrible teachers. IMO, the best thing you can do if to stop putting the blame of your child’s lower grades on the teachers, and start focusing on how your son can succeed in his coursework no matter what the situation.
My D’s AP chem teacher her senior year was brand new. She knew absolutely zero, made mistakes daily in class that the students needed to point out to her, put material on tests that was chapters of ahead of what they were covering, etc… (She was demoted after that year and eventually left the school but again, too late for my D). My point is that D ended up in a study group of friends that taught themselves. They used a bunch of online resources, they got help from another science teacher, and elicited help from some college students. They in turn starting tutoring other students in the class. Was it irritating and unfair? Sure. Was it an amazing learning opportunity? Absolutely yes! Those skills have followed her into college where she’s already had a prof that spoke english so poorly no one understood him.
In the end, your child’s grades are his own. He needs to figure out a way to be successful regardless of the teacher/environment. It only gets harder in college (and I too would not use CC courses as a gauge for difficulty. My D’s DE classes were much, much easier than her AP courses, and a joke compared to what she’s taking now in college). There will be no hand holding in college. Students need to seek out their own resources, self advocate, and figure out how to do well. There is no blaming a prof for poor performance.