It is argued that the close relationship between learning and testing is best exemplified in achievement tests, which are designed both to reinforce learning and to provide feedback about the effectiveness of teaching. Of the four types of achievement tests (placement, formative, diagnostic, and summative), two (formative and diagnostic) are examined in greater depth, and their rationales, functions, and the principles underlying their construction are analyzed. The instructional value of achievement tests and their relationship to motivation, retention, and feedback are reviewed. Reading comprehension testing is discussed in this context, and a sample test designed to enhance learning as well as test skill is presented. (MSE)