Stuttering is very common for young children. The vast majority grow out of it by 7 or 8. It sounds like you stutter as well, so there might be a genetic link. My suggestion would be to continue with speech therapy, and just be as supportive of his speech as you can. The last thing you want is him developing anxiety around speaking, because as we all know, that just compounds the problem. How you go about doing that is something I can't advise on (you're a parent, I'm not, so...), but that's my best advice. Make him comfortable with his own words however they may be formed, and even if he stutters he will be able to manage it emotionally.