Speech therapy was a game changer for my son. It didn’t necessarily “fix” his speech but he knows that he stutters and that’s ok. He was taught techniques to talk a bit slower but those just never 100% fix the speech. His school had him see a therapist twice a week and they were extremely good . I am my child’s biggest advocate. He is very smart and plans to be a surgeon ( he is much older than your son but diagnosed a bit later than your son). Look for speech therapist that specialize in stuttering or speech disfluency.