My 13yr old son has a stutter and im at a loss how to help him.

My 13yr old son has a stutter and im at a loss how to help him. Brief history. Started around age 6. Got worse (still getting worse IMHO). He stutters almost every word. Its hesitant rather than stammering. He claps, jerks his body, dances, flings his hands, tenses his face until hes beetroot, speaks in a foreign accent. He's a happy soul and says no-one mentions it at school. I cant believe that, we all know what schools are like if you're different. We had a short stint of speech therapy. The lady spoke quietly and calmly, so did he. Leave the room and the stutter returns - he hated it. We went back when he was older, still hated it and to be honest, I felt it was absolutely pointless, however the decision to quit was his. Im sorry but playing Connect 4 whilst whispering to each other would only last so long. He reluctant to deal with people - cashiers etc. School pantos were a trauma. I cried when he got through some lines with too much stutter. A 30 odd year old bald man crying at his sons panto. Sometimes we're in the car, he starts a sentence and gets stuck. Hes stuck for so long I check the mirror to see if hes dozed off. By that time his little brother has usually butted in. Dont even get me started on the Hey Google or online games with his mates, we do have some laughs over it. On occasion hes shouted or sung a full sentence, no hesitation. I had a stutter, it wasn't as bad. I still do but you probably wouldn't tell. I've kind of developed a sense of where i will get stuck and change the wording to suit. This means i'm like a human Thesarus lol. I also use ermm a lot, and deep breaths when i'm calling someone. I just want to do something for him. Something productive, not supportive - he gets that anyway. Something practical that he can call on when he struggles. An hour a week away from everyone, just me and him out walking or sat in Maccies. Im looking for advice what this could be. Happy to consider anything that a 13yr old might tolerate. Many Thanks.