I know a fair bit about stammering as my DH is a severe stammerer and it has held him back a bit and my DS1 sometimes stammers. Usually stammers resolve themselves and don't become an ongoing problem. Does the stammer come and go? My son's Speech & Language Therapist said that if it varies and isn't constantly there that's a good sign that he will grow out of it. Just keep an eye on it, don't interrupt him or try to finish anything he says/ guess what he wants as that will lead to frustration and make it worse. I know of friends whose children have developed a stammer around 6/7 and it has just disappeared over time. HTH.