In this article, the authors describe a fourth-grade lesson where 3-D printing technologies were not only a stimulus for engagement but also served as a modeling tool providing meaningful learning opportunities. Specifically, fourth-grade students construct an argument that animals' external structures function to support survival in a particular environment. To develop the lesson, the authors used design-based modeling, a form of instruction in which students engage in engineering design process to develop scientific models that assist in scientific argument (Penner, Lehrer, and Schauble 1998). This article walks readers through the purpose of the model, design challenge, first modeling iteration, second modeling iteration, construction models, model use, model evaluation, revising the models, and assessment.