What Is the ACT®?
Like the SAT, the ACT is a nationally administered, standardized test that helps colleges evaluate candidates. Colleges now accept your ACT or SAT scores interchangeably—in which case you may want to decide if the SAT or ACT is better for you. It’s also common for students to prepare for and take both exams.
Generally, you'll take the ACT for the first time in the spring of your junior year. This will allow you enough time to retake the test during the fall of your senior year if you're not satisfied with your score—and to reserve the summer months for college applications.