Mmzz your experience with maths revision lesson has brought back a memory from my A levels.
We had a nice but not good biology teacher. One of my friends got a tutor (unusual in my 1980s comp) and didn't attend revision sessions. The teacher was furious and told the class
"I have been to the head and told him I don't accept responsibility for her grade."
Of course tutored girl came top of class with a B. My friend and I came next with Ds and the rest of the class got lower. Dreadful.
The three of us that passed went on to do science degrees/careers. Fortunately our other grades were strong and some nice admissions tutors took pity on us. The rest of the class wouldn't have been so lucky.