Thanks for the replies. It appears its all on him. Is there anything his his POP can do to assist (ie. books for studying,a couple of flight lessons, etc.)?
Waveraider... it is great to hear such interest in the career of your son. ARCO has a book out that is a GREAT study guide (just go to amazon and search ASTB or "military aptitude test"). Some others said to get it done as soon as possible, and I completely agree.
As I am sure you already know, sometimes the military can have other plans for your son. Here is one thing to keep in your back pocket. IF things do not work out (as in my case six years ago), there is a program called Field Accession (or fleet accession).
In TBS I expressed interest in flying, but not enough for my CO. I stuck with my ground contract and put down infantry as my #1 but ended up with artillery. I did over two years in the fleet with one deployment to Iraq. I applied to the board (which will come out in a MARADMIN) and got accepted. That was over three years ago and I am STILL in school! So far I have loved this program because my ground experience is irreplaceable and I had a blast in artillery (no pun intended). Anyways, good luck with everything and I hope things work out!