I have one friend who has a hard time understanding things other people say. While everyone except him understands what someone tried to say, this guy still understands nothing. We always have to explain more and more until he can get it. What can we call him?
It's the same as the student who hardly understands what a teacher says while other students can understand it. (Does not mean he is stupid. He can do the exam well. But the teacher has to speak more than usual.)