Just responding here to say that I have been stuttering severely since I was 4 years old (im in college now) and in my experience almost all of my teachers in middle school and highschool were willing and understanding to work with me as well and allowed me to give presentations 1-on-1. I do remember sometimes before the school year, my mom would come in with me and we would explain the situation and find ways to work around it. But i'm sorry you're going through that I can imagine it feels so much worse seeing it happen to your child instead of yourself. However, I would say if your child has accommodations the teacher has to give a work around and can't give a 0 and if they just don't think it's real or want to work with you, if it was me I would speak to a higher up such as the principal and try to figure out a solution from there. Hope it all works out!