A discussion of the Demographic Transition is included in many Environmental Biology or Environmental Science classes. The Demographic Transition occurs as a nation becomes more urban and wealthy, and was widely observed in the twentieth century. The phenomenon includes decreasing family size (fewer children) across generations. In this classroom exercise, students provide numbers of children in past and future generations in their own families, and then the class analyzes the pooled data and hypothesizes why and how this change in human population biology occurs. (Contains 1 figure and 1 table.)