Hi, SLT and stammer ally here 🙂 The approach you mentioned is parent-child interaction therapy. In UK it is based on research from the Palin centre. The Lidcombe program has an evidence base but it can cause children to take the message that stammering is undesirable/not good and this can cause more difficulties with confidence in speaking. Some really great resources to read for positive approaches and philosophy of stammering are Stammering Pride & Prejudice book, Chris Constantino, Courtney Byrd, Stamily, Stutter with confidence on youtube, StutterTalk podcast and redefiningstammering.co.uk. You will be a great ally and champion for your son regardless of how his speech flows out 👊🏼