Individuals vary in their responses to incentives and opportunities. For example, additional education will affect one person differently than another. In recent years, econometricians have given increased attention to such heterogeneous responses and to the consequences of such responses for interpreting regression estimates, especially regression estimates based on instrumental variables. In this article, the author offers illustrative cases with which to introduce masters-level and advanced undergraduate students to the interpretive challenges posed by heterogeneous responses in econometric models.