Most kids grow out of their speech issues with the proper treatment. My wife grew up poor and there wasn't any proper speech therapy when she was young and despite the support of her family (her dad also stutters - it's genetic) my wife unfortunately still stutters. However she told me that she's convinced if she was taken speech therapy classes and knew techniques of controlling it and eventually overcoming it - she would not stutter now as an adult. Continue sending your son to sessions, be supportive and understanding and I guarantee you that all will work out! :)