I had a similar situation.
Straight A student. In my Senior year. Taking Calculus.
There were two pre-Calculus teachers and only one of them also taught Calculus.
If you were unlucky enough to have had the teacher that didn’t teach calculus, you were failing. If your pre-calculus teacher was now your calculus teacher, you were getting A’s.
The calculus teacher had reasons...you will get used to her methods, there was a “trick” to taking her tests...
My dad was a teacher at a different high school. He went to the Parent’s Open House and confronted her in front of all the other parents. After she gave her lame excuses, my dad said...
“I have been teaching for over 20 years. I have two masters degrees in education and enough credits for my doctorate. It is my opinion that this teacher is incompetent and I am removing my son from her class. I suggest you do so as well.”
The class went from 30 students to 13.
Holy crap: We could have been in the same class (you described my situation to a T).
Except my calculus teacher wasn’t female…
Ironic.