Please reach out to his school and ask the school SLP to be involved. He may qualify for an IEP for school based speech therapy, which can include (A) learning about stuttering and speech production, (B) counseling about confidence in communication and learning that his voice is important and how to advocate for himself, and (C) if there are other kids in the school who stutter, he can build those connections. An IEP an also set up useful accommodations that support his learning in a way that lessen his discomfort in class (e.g. no popcorn-style calling to read aloud, options to present to teacher alone instead of in front of the class or to record, etc.).