Hey, we got the same job! Except I'm the stutterer and I've never came across any student so far with a stutter. Just treat them normally with respect and compassion like you would with any other student. Smile, maintain eye contact and let them finish their sentences without interrupting or putting them under pressure to rush it. When we stutter, it's not always to do with anxiety or nerves so it's often nothing personal against you and no need to bring it up to the student, it can often just happen but doesn't have to be made into a huge deal.