Yes I know that researchers haven't evaluated whether or not voice therapy exercises improve fluency. But if wait for others to find the answers for us, we'll be waiting for a long time. Or we may never solve our issue. We can't just wait for sure fire cure or treatment to be produced by researchers. Unfortunately funding for research into stuttering is low. I suspect a cure or a research backed treatment for speech disorders like stuttering will come from something like stroke or Parkinson's research due them having way more funding and interest from society as a whole. I suggested these exercises because I'd help reduce tension in his vocal chords caused by repeated blocking on sounds as well as strengthen them. Strong vocal chords can help reduce blocking on phonetic sounds that require the activation of vocal chords such as stop constants, vowel sounds and diphthongs. This is just one avenue for self therapy. He can do speech stimulability exercises which do have some research behind it. Or he can read out loud.