I dunno. To me, 3.5 seems mad young to be starting therapy. He might well have outgrown his stutter by the time he's 5. Does he notice his stutter? Does he comment on it? When I was a kid, I never realised I actually did stutter until the grown ups in my life pointed it out to me. Honest advice, I'd knock the therapy on the head. Just ignore his stuttering completely. Let him be a kid and just play.