Maintaining a balance between population and the resources needed to sustain life on earth is a critical challenge. This teaching unit focuses on this challenge by providing teachers with information and activities on both the national and global impacts of population growth. The document contains: (1) basic information about the population challenge; (2) some techniques for helping students understand large numbers; (3) a riddle on exponential growth; (4) a quiz on population and the environment (along with an answer key) which can be used in connection with an insert; (5) a list of statements for student reactions; (6) classroom and out-of-school activities; and (7) a listing of fact sheets, films, brochures, newsletters, and teaching kits that deal with population. A special insert, "The Population Challenge," provides additional background information on this issue. The insert contains a call for a need for greater awareness, explanations about the earth's life support systems, and options for individual action. (TW)