The accuracy and fairness of standardized testing is taken very seriously in the education world. These issues are a major focus of both the testing experts who develop standardized tests and the researchers who endeavor to ensure a test's fairness, reliability, validity, and accuracy. But many issues remain both controversial and complex. The National Research Council (NRC) of the National Academy of Sciences issued a report in 1999 from its Board on Testing and Assessment. The report found that educational tests generally do provide dependable and valuable information about student achievement, but that they are definitely not perfect. The researchers pointed out "... a test score is not an exact measure of a student's knowledge or skills...no single test score can be considered a definitive measure of a student's knowledge." The report added that large-scale tests often use different versions of the test form to prevent cheating and that an individual's score can be expected to vary somewhat across different forms of a test--even though test developers try to keep the forms at about the same level of difficulty. Scores can also vary due to "transitory factors," such as the student's health on the day of the test, test anxiety, and other testing conditions. (Contains a list of 5 resources.) [This article was produced by the Center for Assessment and Evaluation of Student Learning (CAESL) at WestEd.]