Nephew that stutters

Nephew that stutters I have a 10 year old nephew who stutters and other than me, my mom and sister he doesn’t say much to people he starts speech class this week, but I’ve noticed when he’s playing video games with his friends or just randomly talking to himself about something on his phone there’s no stutter he speaks so clear Only when he’s taking to us about things he likes and needs he stutters I’m so confused.