Allow him to make mistakes, don’t rush to interrupt and correct him every time he stutters. The adults in my life interrupted me and made me repeat myself whenever there was disfluency in my speech. This had zero positive effect on my stutter, and a very negative effect on my developing personality. My stutter did not improve until people paid less attention to my speech, and I could attempt to stumble through the blocks without interruption. As an adult the stutter is still there, but is mostly unobtrusive.