Should say "a kid who stutters". Yes, but not to "explain" his stutter, but just to say that he does. I know it would take a lot of courage, but if his teacher and fellow students are laughing, he's got to do something. His teacher would be the ideal person to do it , but if not, it'd be good for him to do it. He needs to stop hiding. One statement I learned in speech therapy and I never forgot it: "Do the thing you fear". Fear holds us back, especially if you stutter! Fear of stuttering, fear of failure, etc. It's hard work, get support, don't give up.