Thanks for all the advice everyone. I am hoping that once the regular teacher returns we'll be a little more settled. When this teacher took over the class she asked to delayed Connor entering into her math class for a week while she "got to know him" in reading (which he had already been in for a month) first. From what I understand she is an older teacher who teaches in more traditional ways than what is common at the school (a charter STEM school)-- i.e. she has been teaching math to the whole group whereas the regular teacher usually splits the class into smaller groups.
I also had a discussion with him about other ways he could deal with his frustration besides getting mad. I tried to suggest that he could raise his hand and ask the teacher when he had a question. His first response was "No, her voice is too loud and it hurts my ears." He has always had sensory issues especially regarding sounds so I don't know if this is legitimately the reason he doesn't want to ask or if he is just making excuses to not ask (he has NEVER liked asking for help). We also discussed the idea that things that are difficult can be very good for your brain. He loves anatomy and can relate to the idea of your neurons making new connections. I am hoping that we can help him find constructive ways to work through this. Any advice on how to help him handle his frustrations better?