Those who are charged with the evaluation of an educational program or school or effects of teaching often must consider how well students do on the variety of standardized tests they take in the course of a school year. This overview describes common types of tests students take in large-scale programs. Criterion-referenced tests are tests that measure knowledge or skills that students should have mastered. They are based on grade-level curriculum guidelines. Norm-referenced testing is quite different in concept. Test developers administer a pilot test to a representative group of students, compute average scores, and then compare student achievement on the tests to how well the average student performed on the pilot test. Performance based tests are usually paper and pencil tests that are not multiple choice. Such tests are used to assess writing skills, computer skills, or skills in a field such as the performing arts. Using test results and other assessments, the comparison of schools and school districts can be problematic. For this reason, the idea of "value added" or gain score measurement has been adopted by some tests to measure a student against his or her own previous performance. This overview of testing and test concepts may help parents, teachers, and community members in discussions of the various tests administered in a local school district. (Contains 15 references.) (SLD)