Principles of test administration, test validity, and accuracy of measurement underlying interpretation of standardized test scores in educational administration, instruction, and guidance are presented. Types of norm-referenced score transformations, including percentiles, standard scores, and grade equivalents, and of criterion referenced scores, including content scales, predicted scores, and expectancies, are described; and their applications are illustrated. Special attention is given to multi-scores tests and the representation of their scores as profiles and similarity indexes. (Author)