Are test prep book tests harder than the real tests?

<p>I was wondering if anyone who took the SAT subject tests in any math or science subject could give me their opinion on this.</p>

<p>I have a bunch of tests kids took as a "pre-test" for a free program, and I'm concerned some of these tests are harder than the real test. The tests are from:</p>

<p>Math 1 and 2, REA book
Chemistry, REA book
Physics, Princeton Review book
Biology, Princeton Review book</p>

<p>If you used any of these books and took the practice tests, did you think they did a good job of predicting how you'd do, or do you think they were harder (easier) than the real thing?</p>