This is a tricky situation, because you want your child to have respect for people who are teaching him, but obviously he knows what's going on. I think he's old enough that you can have a conversation with him about what's going on, but maybe put it in different terms so he doesn't feel like she's intentionally being rude to him, even though she appears to be. Maybe say something like, "your teacher isn't used to working with kids your age, and so she might treat you a little differently, even though she doesn't mean to." I would encourage him to speak loudly and clearly in class, then at least all the other kids will know he gets it, and perhaps he can win over the teacher through the other kids?
I can't see that it can hurt him too much if he likes it so much despite the mistreatment, and if you can explain that not all teachers are like this.
