Stuttering

My nephew is in 4th grade and many times, he will shudder at the very beginning of what he wants to say, then he says it. For example he may say, “I I I I .... I know it’s great to be able to do gymnastics!” I know he may out grow this. My brother did the same thing when he was young, and he out grew his studdering. He doesn’t studdering at all now. My nephew’s parents wonder why my nephew shudders... what causes him to studdering? Is there anything he can do to help stop his studdering?