Unfortunately because of my stutter and severe anxiety in a negative feedback loop I had an absolutely terrible time in middle and high school. ESPECIALLY middle school because my stutter peaked and the bullying was relentless but I was too small and anxious to fight back. I never joined any clubs, never hung out with any friends (had none at the time because of it), never had a girlfriend (until age18 at my HS retail job where no one knew me so I could reinvent myself), never played sports etc etc. My stutter did go away on it's own when my voice changed at 16 but the damage was done and I was viewed as a total outsider by everyone. The year after that I took up weight lifting, stopped giving a crap and had a real F everyone mentality that might have been more harmful than good but whatever. Yes he's going to have to work through it, yes it'll be one of the hardest things he's ever done. I strongly recommend talk therapy as getting over anxiety made a colossal difference in my stutter but each case is unique and it might not make a difference in his stutter. Even if he doesn't have anxiety someone non biased to talk to can make a huge difference too. The biggest tip for stuttering I learned is to sandwich hard words mid sentence so that the airflow is there and it becomes so much easier to speak (for me atleast). Hope this helps, stuttering as a teen was torture.