<p>The ACT is a better reflection of the typical high school curriculum than the SAT. It is created based on studies of high school curricula in the US, and is intended to measure how much students have learned in high school--academic achievement rather than aptitude. While I'm not convinced that the two tests really measure anything different, I have found that the content of the ACT is much more like high school work. The readings on the SAT are more difficult than what high school students are typically expected to read. The ACT also includes a science section. A full ACT practice test is available here: <a href="http://www.actstudent.org/sampletest/index.html%5B/url%5D">http://www.actstudent.org/sampletest/index.html</a>.</p>
<p>If you want to know what more advanced high school students learn in the US, go to the <a href="http://www.collegeboard.com/student/testing/ap/about.html%5B/url%5D">http://www.collegeboard.com/student/testing/ap/about.html</a> and look at the content covered by the AP tests in Physics, Biology, and Calculus.</p>