From Quora: My Answer to "What type of student is more likely to do well on the SAT vs the ACT?"

https://www.quora.com/What-type-of-student-is-more-likely-to-do-well-on-the-SAT-vs-the-ACT/answer/John-Linneball

The ACT is better for you if you can pound out simpler math questions in less time (you get 60 minutes to do 60 problems); the SAT math is better if you can handle questions that are trickier (i.e., there’s a shortcut you need to find to do it quickly). If you take the SAT, you do also need to memorize the basic formulas the SAT provides, but you really should know most of them in any event. ACT math asks you to plug values into some scary-looking formulas, and the SAT asks you to manipulate some formulas. If you get past the weird decimals, variables, etc., the actual math is very easy in both types of “formula” problems.


As others have answered, the “new SAT” is very similar to the ACT. The SAT has added charts and graphs to interpret, in response to the ACT’s science section, which mostly should be called the “Data Interpretation” or “Can You Read Charts and Graphs?” section, since you need only know very basic science to do the problems. (You do need to know some basic science facts such as the charge of an electron, what photosynthesis is, etc., but way less than I’d expect anyone who’s about to graduate from high school to know.)


The reading sections on both tests are very similar - it’s a wash. You won’t see any real differences between the two. Both test vocabulary in context, details, main ideas, and inferences from things implied but not stated in the text. They’re both frustrating in that the hard questions can present very subtle shades of meaning where many students lose points for picking answers that are perfectly good answers, but not the “best” answers according to the test makers.


The English/Writing tests are identical - the College Board basically copied the ACT’s test wholesale, then added a few charts and graphs, when they came up with the “new SAT.”
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The essay on the SAT is probably harder for most students. While the ACT just asks you to analyze three perspectives on an issue, then present your own (or just explain which of the three you agree with), the SAT requires you to analyze the arguments in a persuasive essay (e.g., a newspaper editorial), explaining how the argument is presented and NOT whether you agree with it. So if you aren’t familiar with the terms “ethos,” “pathos,” and “logos,” don’t like it when you can’t express your personal opinions on an issue on which you have strong feelings, etc., or just didn’t do that well in English classes where you had to analyze the texts you read for technique, rather than simply explain what you just read, you’ll find the ACT essay easier to handle. It’s closer to the essays you had to write from grade school on; the SAT is more of a 10th or 11th-grade assignment.