Through a series of four successfully field-tested activities, secondary students examine the changing age structure of the U.S. population and consider some of the implications for the future as the proportion of elders increases and the proportion of youth declines. In the first activity "Age/Sex Pyramids," students use population census data to construct age/sex pyramid graphs for the years 1960, 1975, and 2000. "Age Dependency Ratio" is examined in the second activity. Students compute age-dependency ratios for each of the age/sex pyramids and discuss possible effects on society. The age-dependency ratio is a number value that indicates the proportion of nonproducing numbers in a population compared to all members of that population. In an evaluation exercise for the first two activities, students are required to construct an age/sex pyramid for Mexico, demonstrating their comprehension of the objectives of the first two activities, in a cross-cultural setting. The third activity deals with the "Economics of Aging." Students examine data on the economics status of the elderly with a focus on social security and discuss alternative plans for meeting the future needs of the elderly. "How Would You Vote?" is the topic of the fourth activity. In a simulation game, students play the roles of elders making economic and political decisions and examine how shifts in population from one age cohort to another affect the political climate. The third and fourth activities are evaluated through a test and an oral review. Teachers' materials, transparencies, and student handouts are provided for each activity. (Author/RM)