Tests are samples of knowledge, skills, or other qualities that are used to make inferences about students, teachers, schools, or other components of the education system. Achievement tests are widely used to make inferences about knowledge and skills that have been acquired through instructional processes and are thus a common feature of educational settings around the world. Achievement tests are often contrasted with aptitude tests, which were traditionally used to make inferences about test takers' innate capacity, potential, or intelligence without the influence of instruction. This entry discusses some common forms and uses of achievement tests. It also considers issues related to fairness in using achievement test scores.