As he is a specially-abled person, you can try to make him feel more comfortable. You can try to be friendly with him as much as possible. You can try to protect him from bullying. You can talk to those students who make fun of him. You can make them understand that bullying someone is not correct. You can have a good talk about not making fun of him. And even after that, you can complain about this to your class teacher if they don’t change their behavior.