Why would a person make A's in Calculus 1A, and then have trouble passing 1B?

Math is not my good point, so I can't help this person. My son had one teacher for Calculus 1A and then a different teacher for Calculus 1B. He can't stand the current teacher, and from what he tells me, the rest of the class is having trouble with the subject and the teacher's attitude. He says no one questions the teacher's ways because it's a prestigious college in California, and this teacher is supposedly some brilliant math professor. We're spending a fortune on the tuition, and my son now feels like a failure though he claims he is studying harder than he did in 1A. This teacher says that he will fail the entire class if he has to in order to make believers of them, in that they have to work harder. Does anyone have suggestions?