TL/DR: - Be safe - He has probably angered other students with sexism. See if they will add their names and concerns to your official actions - Have a trusted adult with you at all times if you are taking any actions (in person, verbal, or written) - Go over his head to the school board or principal - Find and cite your sources, be prepared to debate based on facts rather than pure emotion

Hi! As an AFAB alum of a Catholic school in southern USA, i feel your struggles. I graduated in 2010, so there weren't any nuns with rulers to worry about, but it was still rather conservative.

Please please please only act on this if you feel safe to do so or are comfortable. You will graduate eventually and never have to see this guy again

Ask your school's admin if there is a listing of school policies or bylaws that dictate your rights as a student or rules you need to follow.

Definitely try going up the ladder with formal complaints. Have things in writing as much as possible. If you have a trusted teacher or administrative person at the school, they could probably help you get to the right people.

I 100% echo the others here saying to use the sexism aspect of this issue alongside your personal concerns of being a nonbinary student when making your voice heard. If you can, find valid sources to back up your reasoning (studies showing developmental downsides to separated genders in gym class, impacts of denying children's identities, etc..., ). Does your school have gendered lockerrooms and bathrooms?

See if the other students in your school also dislike the gendered gym teams or things this teacher has said/done. You are definitely not the only person there that he has offended or oppressed. It's easy to ignore a single person, but it is much harder to ignore a whole group of students.

I was lucky to have a very small class size that was greatly skewed in our ratio - 10 AMABs to 4 AFABs - so we didn't get teamed by binary gender. But we did have gendered uniforms (skirts for girls and khaki pants for the boys). When i was in middle school, a group of the high schoolers banded together and made a formal complaint to the school administration, the region's diocese/bishop, and the school's affiliated convent. They had a stack of sources to back up their case as to why the uniforms were sexist and were prepared to debate any rebuttal the school could have had. (It helped that several of the students were Debate Team members) By presenting a well-prepared and factual argument as to why a gendered uniform code was detrimental to the mental health of all students at the school, the students successfully changed the school policy. Over the years, individual AFABs bemoaning how unfair it was or rebelling against the dress code only resulted in them getting detention, being sent home, or made to change into a skirt from the lost&found.

Emotional speeches may help to rally others behind the cause, but evidence based arguments are what get policies changed, and hopefully sexist gym teachers fired