I. THE construction of standardised tests for the assessment of personal characteristics and the measurement of human abilities has made it possible to study the behaviour of individuals and of groups with greatly increased accuracy. Through the use of such instruments a teacher can learn in a few hours as much about the present performance of his pupils as he could formerly have discovered in rnany months of ordinary class-room or club contacts. It is, therefore, desirable for educators to become familiar with the administration of such tests and with the interpretation of statistical terms often used in discussion of their results.