Most colleges require that students take either the SAT or ACT to be considered for admission, and students and their parents may spend thousands of dollars preparing for these standardized tests. The use of these tests, however, continues to be debated, with testing organizations advocating for their validity. Some organizations -- particularly those advocating for the rights of minority groups -- have raised concerns about testing bias.

Achievement vs. Aptitude

While both the SAT and ACT are given in a quiet, standardized testing environment, the two tests purport to measure different things. The ACT is an achievement test, which means that it measures what students have learned and tends to have direct, clearly-written questions. The SAT, by contrast, is an aptitude test, which means that it measures a student's ability to learn and frequently presents problems in ways that challenge students to solve logical puzzles. Consequently, the ACT may be a better measure of study skills and learning, while the SAT could provide a better assessment of aptitude. However, no test can accurately measure aptitude alone since certain skills must be learned even to take the test and students routinely improve their scores through practicing the test itself. Similarly, the ACT cannot measure the full range of skills needed for success in college.

Predicting College Grades

Both the College Board and ACT, Inc., argue that their tests are designed to predict first-year students' grades. The National Center for Fair and Open Testing, however, points out that research done by the tests' creators indicates that high school grades more accurately predict college success. The tests do, however, provide some clues. The SAT may measure a student's ability to excel in school because it is an aptitude test. The ACT, by contrast, could be a partial measure of how hard a student works. Because the test is an achievement test that measures what a student has already learned, students who excel on the test may be those with better study skills and learning strategies. However, a 2011 study published by the "National Bureau of Economic Research" found that only the math and English sections accurately predicted college grades.

Testing Bias

Both the ACT and SAT have undergone several revisions to prevent testing bias, the tendency of a test to favor one group over another. For example, according to a 2011 "MIS Quarterly" study, students may under-perform on a test when the test uses cultural language or unfamiliar terms. For example, a word problem that mentions porcelain and china could confuse a student who had not been exposed to either. Stereotype threat -- the tendency of a person to perform poorly when reminded of negative stereotypes about her group -- also remains a problem. Women, for example, may do poorly on the math section when they have to check a box indicating that they are female, according to a 2012 study published in "Educational Psychologist." Because testing bias primarily affects minority groups, test scores may be more valid in non-minority students.

Other Testing Factors

Individual student experiences can affect the validity of test scores, as well as their predictive value. For example, a 2011 "Journal of Educational Measurement" study found that students from low socioeconomic backgrounds tend to receive lower college grades than their test scores predict. This could be because of the added stress of financial demands placed on poor college students. Students who are under stress, overtired or ill when they take the test may also perform poorly.