Modeling is one of the scientific practices featured in the "Next Generation Science Standards" ("NGSS") (Achieve Inc. 2013). This practice is central to the work of science because modeling activities can prompt new questions for investigation, which, in turn, can lead to evidence and information that can be incorporated into a revised model. Models can also support explanations of natural events and processes. Creating and modifying models in response to evidence and the arguments of peers helps students reorganize their understanding of important science ideas (Lehrer and Schauble 2003; Windschitl, Thompson, and Braaten 2008). Students use models as instruments for doing public forms of reasoning, which can be difficult unless you have ways of making student thinking visible. In this article, the authors describe a "toolkit" of different representations of student thinking for use in the classroom. Some are types of models, and others are ways for students to make links between the activities or readings they do and the development of the models.