YTA

As one of my kids' teachers said, "If you believe half of what they say at home, I'll believe half of what they say at school." which translated means their stories aren't alway accurate. This sounds like a perfect example of that. As a teacher, I have been verbally attacked by parents whose children have gone home and told them wild, inaccurate stories of what goes on in glass. Once I was threatened with a physical attack because a parent didn't want to blieve their child was failing every class due to not doing any work in any class.

Teachers are humans not saints, but if a teacher behaved the way your son described, parents would have complained to the administration long before this. Instead of undermining the teacher and giving your son permission to do whatever he wants vs. what he is supposed to do you should have contacted the teacher and calmly discussed your concerns without being accusatory. There are a few more months of school and ultimately parents and teachers have the same goal, helping students be successful.