Well all that you can do is just take it easy because to deal with stuttering in school is very hard, you can't do nothing about this, just if you have magic to cure his stutter but nobody can't, all you can do is to be patient and smile soft when he will start to speak, because is not easy for him to deal with stuttering everyday and to speak with his friends, you speak with him soft and short and make him to feel comfortable, and if he will start to stutter don't stop it because if you do, he will feel even worse, just smile soft and speak with him short, and if u know say a meme to laugh for it, he will feel quiet.