Context: I am a 17 year old boy, currently in a middle school. I also go to extra coaching classes after school for Mathematics.

Here's the problem: I don't feel good in the coaching centre that I go to. This is because the teacher over there constantly passes comments on me in my absence, as well as when I am present in the class. He also talks about my parents in a very disrespectful way. This all is affecting my mental health and I want to stop going to the coaching. But my parents are forcing me to attend it anyhow.

I told them about my problem, but they say that whatever the teacher does or says is for your good! They just console me and tell me to focus on my studies. But, not only am I not able to focus on studies, but this all is affecting me in a negative way. My term end examinations are appearing in a month. So, I reluctantly have to go the coaching. But I want to leave the coaching now.

How can I convince my parents to make me quit the coaching, and tell them that I can score good grades by self studying?

[I don't know what are the appropriate tags for this question. Someone please fix them.]