Advice for the mom of a child with a stutter?

Advice for the mom of a child with a stutter? Hi all: My husband and my 12YO son both have fairly severe blocking stutters. My husband has been a lot of help to me in understanding stuttering and helping me to support our son, but they are very different people (introvert v extrovert, not anxious v anxious etc) so I was hoping to get some other ideas here. My son INSISTS that he does not want to go to speech therapy and so far we have honored this request (the school does not provide any support unless the stutter "interferes with learning" which they have determined his does not, though I am not as sure). He has many kind friends and is well liked, plays sports, and says he is not being teased or bullied. He does not seem embarrassed or ashamed of the fact that he stutters (dad has helped SO much with this), but I know that the stutter causes him a lot of frustration, and he often lashes out when he has to repeat something (I have mild hearing loss so unfortunately this occurs rather often), when he is interrupted, or when he feels that he is not being heard or understood. He also talks VERY fast. I also suspect that he is avoiding talking in some circumstances. As someone who has been married to a person who stutters for 30 years, I totally understand where these behaviors are coming from but I would love to help him try to reduce his frustration and especially the lashing out. (Interestingly he has learned that he does NOT stutter when he yells, so this has caused him to start yelling earlier in a conflict than my other son who does not stutter). What do you wish the most that your parent would have done to help you and support you when you were growing up with a stutter?