SAT subject tests, formerly known as the SAT II’s and the SAT achievement tests, are subject specific tests that are designed to measure a students’ knowledge in a particular area. There are subject tests in each of the five core subjects of math, science, history, English and foreign languages. Most colleges do not require a student to submit the scores from the SAT subject tests so for many students these tests need not be taken. However, many of the most selective colleges do require or recommend that the student submit the scores from several of these tests.
Students are generally advised to take a subject test after they have finished a course of study in that subject so that the material will still be fresh in their minds. This applies to most of the subject tests except for the foreign language tests and math tests. For these two types of test, having several years of study in the subject is more helpful before taking the test.
For each of the subject tests the College Board provides a list of anticipated skills and recommended prep.