Maybe it helps, if you tell him to listen to his anxiety to become tolerant against it. Maybe, if he becomes mad at himself, just notice these thoughts and feelings and realize that this increases his stuttering and then accept and let go or he can learn to stop reacting to his stutter (thoughts), for example, stop becoming mad when he stutters. Instead of focusing on 'reacting' \[becoming mad\], he can focus on the anticipation feelings and the stutter feeling to learn that it's not fearful/true/true intention Old habit: if he anticipates a stutter "I see a stutter coming" > he stutters > he becomes mad New habit: if he anticipates a stutter > observe it but don't react to it, learn that it's not real > he doesn't become mad (because he learns to stop reacting)