How do you deal with know-it-alls when they don't give the cl a chance to learn?

The professor doesn't help the situation. He makes comments in front of the cl how she got all the answers right and she was the first person to hand in her test. It disrupts the cl because the students are trying to catch up. The student doesn't annoy me as much as the teacher because he doesn't know how to conduct the cl. If I was a teacher, I would not make such comments.