tickytock, it helps to do the homework.
Good for you for doing so well on the exam!
Cressida, I'd bet your son has some insight into what the problem is, so I'd ask him first. There is NO excuse for a student who gets As in AP courses to get 1s on the exams (barring illness, etc., of course). If I were in your shoes, I'd first talk to other parents to see whether this is a widespread problem, and then to the school.
I'd want to know the AP pass rate of the different AP teachers at the school (assuming it's possible to get from the school; if it's not possible to get from the school, I'd likely start trying to find out on my own, by asking students for data -- their scores, who taught their class -- and compiling the info myself). I'd encourage the students to start looking after their own interests if the AP teachers they are assigned don't, and by that, I mean by self-studying, going through review books, checking the curriculum taught at the school with the suggested AP curriculum (available on the AP web site), taking practice tests, and so on.
Ugh. How awful! I hope the school at least paid for the test!