Unfortunately, he must pass the ASVAB prior to enlisting in the Army. This is a very good site for practice tests and it is legit: http://www.military.com/ASVAB
He can also get the study guides, which are a great tool in preparing for the ASVAB. Barrons is probably the best study guide. That is what I used when I prepared for the ASVAB 16 years ago and it still is the best out there.
As far as the test goes, just have him take his time and answer every question. There is no penalty for wrong answers. If he has 10 questions to go and only 30 seconds, pick a letter and fill them in.
If you have any further questions, let me know.