<p>The recommended prep courses are College Board Blue book that has 10 real tests and Real ACT book (Reddish/White) that has 5 real tests. On CB website you can buy additional services that include automatic essay grader and online real test. Your son has to be self-motivated to go over the tests himself (some in timed fashion, esp. ACT), highlight every question that he is unclear about and find somebody to explain the solution. If you do not have anyone in your family who can help you may want to hire external help (e.g. current college or even HS student that had very high scores himself) just to go over batches of questions that he does not understand.</p>
<p>If you want to enroll him into prep-course - make him talk to the current seniors in his school and on his team, while you can ask their parents. You may want to find out where Asian kids in your area do test prep - they take this stuff seriously. See if you can find a place where they spend every Saturday taking timed test and then review it in the afternoon. Money spent on test prep may be the best investment that you can make but you have to invest wisely. General well known places (Kaplan, PRN review, etc) that hire random people to teach is a hit or miss. Find a local outfit with good reputation.</p>