My first thought was that I wish I had your teacher but I can see how that would still sting if it's obvious that he's exuding you. It might be that he thinks he's helping rather than any malicious intent. Maybe try catching him when the class leaves and just saying you don't mind being asked to read? If there's any sort of obvious discrimination going on despite talking to him make sure you or your parents report it. Stuttering is a recognised disability in a lot of countries so it should be taken seriously if it's affecting your education.