I have not taken the casting exam so I won't be able to answer the major part of your question.
I'm assuming that your son may have already found this web site but just in case he hasn't: http://www.virtualflycasting.com/
This is the exam broken down in small video clips.
http://www.virtualflycasting.com/certexam.htm
I could not get it to work with my Firefox browser so if you use that, you will need to look at these in Internet Explorer. The only thing about these videos that drive me a little nuts is that it is strictly video does not come with an audio component. It would be really nice to not only see the cast but to hear an explanation of how to correct the faults.
NEVER MIND!! I didn't have my speakers on!!
P.S. The site was working this morning but it seemed to be having some technical difficulties later in the morning. Don't give up on it if it's not working right now.