The SAT is administered by the College Board, a private nonprofit organization that also oversees American standardized tests such as the Advanced Placement subject tests and the SAT Subject Tests (more on those later). For many years, while the structure and scoring of the SAT changed, the test itself remained the premier standardized test system used by American colleges and universities. The ACT (administered by American College Testing, Inc.) originated more recently, but in the past few years has overtaken the SAT as the most popular college admissions standardized test taken in the United States.
Up until 2016, the SAT and ACT were very different, as indicated by their respective score distributions. But in 2016, the College Board (likely noticing the declining popularity of the SAT among college applicants) released plans to radically restructure the SAT so that it would test areas more relevant to college success. The SAT's previous focus on vocabulary was eliminated, as it had become apparent that knowing the usage of various antiquated words did not reflect college readiness. Such words were easily memorized and then easily forgotten on the Sunday after the test, unlike genuine prose analysis skills. Another major change enacted in 2016 was the reorganization of the test sections. When I took the SAT in 2014, it took all day. Sections such as "Critical Reading" were partitioned into 2-3 shorter sections--some as brief as 10 minutes--peppered with uselessly short breaks and rapid-fire switching of skill sets between sections. The ACT, on the other hand, was smooth sailing: four sections of less than an hour each, with one break in the middle.
Generally, the 2016 redesign of the SAT made it look more like the ACT —-- an important fact to keep in mind when deciding which test to take. In order to put my own best foot forward in the college admissions process, I took the SAT and ACT twice each. In my own preparation and in the years since, here are the important differences I've noticed between the tests:
1. The most obvious difference between the two tests is that the ACT requires a student to work faster than the SAT does. The SAT Reading section contains 52 questions to be completed in 65 minutes; the ACT contains 40 to be completed in 35. The English and math question-to-time ratios are similarly higher for the ACT, and the ACT science section is a mad rush to the finish. Speaking of which...
2. Unlike the SAT, the ACT tests "science." The Science section of the ACT is the last of the four multiple-choice sections, with 40 questions in 35 minutes. Don't worry, though; the Science section is pretty straightforward once you understand the tricks. The section contains several readings —-- usually excerpts of "lab reports" or similar write-ups from experiments in biology, chemistry, or physics. Each is accompanied by a set of questions concerned with inferences you are expected to make from the given data. These inferences require reading graphs and charts, knowing some elementary science buzzwords like "control group" and "independent variable," and common sense.
3. By all accounts, the reading comprehension on the SAT is harder than on the ACT. Reading questions (often especially difficult for non-native English speakers) on the SAT focus overwhelmingly on the author's tone, argument, intentions, rhetoric, and style. In the ACT Reading section, these topics still come up, but more attention is paid to details and content from the passage itself, meaning that the test-taker doesn't have to "read between the lines" as much.
4. If you take the SAT, most colleges require you to complete some other tests, too. In fact, the College Board has what it calls the "SAT Suite of Assessments": a veritable barrage of tests to complement the general SAT in filling out a student's standardized test portfolio. The SAT Subject Tests are hour-long multiple-choice tests that assess your command of content from a particular course, such as World History, Spanish Language, or Chemistry. If you're a good test taker or have excelled in a bunch of courses at school, you'll be able to add good scores to your profile, which can add extra wow to an already strong general SAT score, or make up for a weak one. Top-tier American universities tend to ask for 2-3 Subject Test scores submitted along with your general score. Most schools care more about your command of actual material than about how well you perform on a standardized tests, so a bad Subject Test score can hurt you. If you aren't required to send all your scores, don't send your weak ones; if you are, retake them so that you can at least show you've improved.
So which test should you choose? It varies significantly from person to person, and depends on one's strengths and weaknesses. If timed tests are your Achilles heel, the ACT is not for you. On the other hand, if data analysis and quantitative sciences come naturally to you at lightning speed, the ACT is a great choice. I you've always struggled to figure out what the author of a text is trying to say, don't take the SAT. If you feel very comfortable with reading comprehension, go for it! Most people are better at one test than at the other, and the best way to figure out which is to take practice tests for both, score them, and then pull up a score conversion chart to discern whether you're testing at a higher percentile in one than in the other.
But do the tests actually matter? Universities are in the business of evaluating undergraduate applicants "holistically," paying attention to facts that they perceive as indicators of the applicant's aptitude and character. This doesn't mean standardized tests aren’t important. You still need to focus on getting those scores--especially English and Reading--to a competitive level.
Don't get me wrong. Institutions are sympathetic to international students with low reading comprehension scores. But you want the case for your admission to be airtight. Anything that could count against you should be eliminated from your application. At top-tier American universities with a ridiculous number of qualified applicants, admissions committees aren't looking for reasons to admit you. They can't afford to--there are too few spots for them to read most applications generously. Instead, they're actually looking for reasons not to admit you. Arrogant-sounding essay? Bad news for you. Weird art supplement submission? You'll wish you hadn't. Low ACT scores? Not an instant disqualification, but if your scores are below the 25th percentile mark at your target institution, your odds start to drop dramatically.
Yes, the tests do matter. When organizing your application, you want to present the best face possible. You should spend significant time diagnosing your test weaknesses, targeting those with your test prep, and working to make your test scores as strong as the rest of your application.