I’m a person who stutters (but now has learned how to speak smoothly) and works in early childhood mental health. I had an unpleasant visceral reaction to your description of the “therapy”. The good news is that he is still soo young so stopping this emotionally harmful technique will dramatically reduce its negative impact. Honestly, it sounds like a version of harmful ABA therapy that is used for children with autism. This linked post is geared toward adults, but it’s still useful information, especially the part that acknowledges the trauma from stuttering can absolutely begin in early childhood. Catching it early, *like you keep doing*, is the most effective way to nearly eliminate the trauma response.