This article describes a lesson in which fourth-grade students create a habitat for terrapins while reducing erosion. A client and their needs were presented to the students: The city purchased a piece of shoreline on the bay previously owned by a private company. The company had started to develop the land, exposing soil up to the water's edge. The city council wants to hire an environmental engineering firm to redesign the shoreline area to solve two problems: (1) too much erosion into the bay; and (2) not enough habitat for terrapins. The goals for student teams were: (1) to design a model shoreline that addresses the problems and is as affordable as possible for the city council; and (2) to present their best model to the city council to compete for the job. After a demonstration of models to begin the unit, the students design their own model.