The ACT is a college admissions test, and most colleges allow students to choose between this test and the SAT. A high score on the ACT can increase your likelihood of getting into college, but schools don't typically use the ACT Compass as part of the application process. Instead, if your school requires the Compass, you'll take it after the college has admitted you.
The ACT test provides a measure of college student readiness but provides no guidance regarding class placement. Your school may use your ACT score to determine whether you're ready for upper-level classes or a specific major. The ACT Compass guides schools about the right math and reading classes for incoming freshmen and provides specific information about your academic skills.
Both the ACT and Compass tests are given in quiet, standardized environments. While the ACT is timed, the Compass test is not, which means the time it takes you to complete it depends upon your overall skill level and working speed. The ACT is a pencil and paper test, and you'll fill in bubbles on an answer sheet, but you will take the Compass test on a computer.
The ACT test is a standardized test divided into five sections that include questions on English, math, reading, science and writing. The Compass, however, is a subject-specific test, so it only tests you on one area of knowledge per Compass test. The five test topics for this test are math, reading, writing, essay writing and English as a second language.