I am sometimes asked if students need to take both the SAT and ACT and the quick answer is no. A student only needs to take one standardized test for college admissions. The question then becomes, which test.
All students should take at least one practice test of the SAT and ACT. The College Board and ACT each offer a free practice test for students to take. The practice test should be taken under standard testing procedures to get the best estimate of your score. After taking each test the student should consider on which test they had the best score and focus their studies on that test. To compare the scores on the two tests, look at one of the comparison tables available.
There are other issues and some of those are reviewed at our page on the SAT or ACT.