My son, a Junior, yesterday received a '5' on his AP practice exam in Calculus BC.
My daughter had a calc teacher that just wanted to be a buddy to everyone, asking what they did over the weekend, what their plans were, etc. Needless to say, that didn't leave much time for teaching CALCULUS! She bought the AP book and learned it by herself.
Only about 5-6% of the students get a 5 on the actual AP test, but she got 5s in all but one of the 8 or 9 AP tests she took (including calculus). She got a 4 in economics.
Best of luck to your son, he has a bright future.
nacl