This booklet gives a brief history of the metric system up to the present time. A detailed explanation of the international system of units (SI units) for length, area, volume, mass, temperature, and time is included. Also included are five check-up tests with answers for the measures of length, area, volume, and weight, as well as tables of all metric prefixes and of practical units for commerce and trade. A third section contains general guidelines for teaching the metric system with specific directions for spelling, punctuation, and use of metric symbols. The fourth section contains classroom activities, lists of recommended materials, and instructions for student-made learning aids. (JBW)