Models may be used for purposes relating (a)~to understanding, predicting, and communicating model aspects, and (b)~to implementing the model and capturing the design intent. Models that are primarily used for understanding, predicting and communicating are referred to as descriptive models, whereas models mainly used for implementation are called prescriptive models. This contribution focuses on teaching both the common and the distinguishing aspects of the two model categories. We start with an example for a general descriptive and prescriptive model, independent of particular software modeling languages, and continue to discuss an example demonstrating how UML and OCL can be applied for specifying both a descriptive and a prescriptive model. Finally, we discuss lessons to be learned from this teaching venture.