J.W.
..basically.. your son cannot process all the information coming into his ears at the same time in order to organize it and then reproduce on paper or on a test..you may also want to try a listening program called The Listening Program.. it's classical music that is specially made to filter in and out certain tones to strengthen different parts of the brain and ear. I had CAPD growing up and essetially still have it. However: i am now a pediatric occupational therapist-very successful. the teacher just need to find ways to help him learn in a more visual way. Ie-have teachers give him written oral lectures or let him copy a friends notebook or let him record the class so he can go back and listen to it to pick up things he missed.
the listening program website is www.advancedbrain.com.. also on that website they have a game that helps which helps with digit spans.. look into it.
my mom got me into a program when i was little that she had to implement at home called NACD. www.nacd.org i truly believe this helped me through school and college..
good luck feel free to email me ____@____.com if you want anymore info
J.