@jaytcee This might not be popular and I've also upvoted most of the other responses, but this one really had some merit, too. My first grade teacher was AWFUL to me. I hated her, because she hated me. I was too talkative at the wrong moments and quiet at the wrong moments. I had better command of my fine motor skills than all of my classmates and a significantly higher reading level, and that irked her. She picked on me so much that I recently went to visit my kindergarten teacher, who my family stayed close with and my sister had many years after me, and HE remembered how much of an outstanding bitch this woman was to me. Over 20 years later!
But it did teach me to excel in the face of adversity, to not blindly accept authority's opinions of me, and that sometimes I'd have to go along to get along. All of those lessons I learned with my parents' guidance, of course. They framed their responses to many of my complaints that way, validating my emotions but giving me the tools to learn how to deal with it rather than run away. I was also 6. And I'm pretty sure she probably made a similar comment about I could kill her at some point about me with something (I think she was overseeing an assembly when I was in second grade and I wasn't being imperfectly still and it was like if I didn't sit still... said to another adult but within my earshot).
What your son is going through sucks. A lot. But if it irreparably damages him permanently, that's in part because you're not using this opportunity to teach him coping skills and rise above strategies. She's of course still the primary one to blame, but use it as an opportunity to build.