This is a common question among high school students. Here are a few major differences between the tests:
1) The ACT has a Science section. The SAT does not. Keep in mind, however, that the ACT Science does not require much outside Science knowledge. It mainly tests your ability to read and interpret data. The SAT does have a few Science-related question in its Reading Comprehension section, where you sometimes must interpret graphs, charts, and data in relation to a scientific passage.
2) The SAT Math has a “No Calculator” section, in addition to a Math section in which you are allowed to use your calculator. The ACT Math is only a single section, in which you are permitted use of your calculator. For some students, doing an entire math section without a calculator seems daunting. Keep in mind, though, that many of the questions on both tests can be solved without use of a calculator.
3) The SAT has two Math sections, broken up into a 55 minute Calculator section and a 25 minute No Calculator section. The ACT has only one Math section, which lasts 60 minutes. So, the SAT is slightly more focused on Math. Math also accounts for half your SAT final score, whereas it’s only one quarter of your ACT score (since the ACT has additional sections.)
4) The ACT Math section has a larger focus on Geometry than the SAT Math sections. The ACT also sometimes has questions related to Trigonometry, Matrices, and Logarithms, which the SAT does not. Keep in mind, however, that these advanced math questions would only account for a handful of questions on the test. Both tests focus heavily on Algebra.
5) The SAT also has “grid-in” questions on both their No Calculator and Calculator sections (totaling about 13 questions combined.) Grid-ins are free-response math questions in which you do not have any multiple-choice answer choices. You must write in your answer yourself. This can seem daunting to some students. The ACT, however, has only multiple-choice Math questions.
6) The SAT Essay requires analyzing a passage. You must discuss how the author of the passage builds an effective argument. The ACT Essay, however, requires analyzing three different perspectives on an issue and taking a position. The SAT Essay is more like the essays you’ll encounter in your AP English classes. The ACT Essay is based more around your opinion of an issue.
Those are the key differences between the tests. However, we always tell our clients to take a sample SAT and a sample ACT test before they decide which test is right for them. By actually trying to work through the problems on each test, you’ll get a strong sense of which test you’re more comfortable with and confident about.