Look into some fun math games and activities. This would not only help you reach the math area you are trying to target, but would also aide the relationship process. I’m a special education teacher with a mild to moderate stutter. I’ve worked with many students of all needs and abilities, and educational games are always a go to. Also, try to find out his likes and interests so you can integrate that into your activities with him. He likes super heroes ? Make a word problem with those names. He likes a certain show? Create a game or a worksheet centered around that show. It can go on and on. Honestly, as a teacher and a person who stutters, I feel that this boy’s stutter is just a small part of who he is, and it just takes some effort to crack that shell. The worst thing you could do would be to finish his sentences or telling him to breath. Just be there, patient, and ready to listen. I really admire your dedication! I’m happy this this boy has a tutor like you who genuinely cares. I wish I did when I was his age. Sounds like you would be a great teacher one day!