Myth 7: If you take the ACT, you don't need SAT subject tests.
It's true at Yale University. It's not true at Harvard. It's true at Tufts University. It's not true at Williams College. In short, it's all over the place. Subject tests are one-hour exams on a variety of subjects. Some colleges and universities (but certainly not all) require or recommend one or more in addition to, or sometimes in place of, the SAT or ACT.
You don't want to stress about a subject test that you won't need, but you also don't want to be unable to apply to a school because you didn't meet its basic testing requirements. Visit schools' websites, see what tests they require or recommend, and plan to take those tests.
Ned Johnson is president of PrepMatters, a test preparatory and educational consulting firm based in Maryland, and coauthor of Conquering the SAT: How Parents Can Help Teens Overcome the Pressure and Succeed.