Modeling is an effective tool to help students access mathematical concepts. Finding a math teacher who has not drawn a fraction bar or pie chart on the board would be difficult, as would finding students who have not been asked to draw models and represent numbers in different ways. In this article, the authors will discuss: (1) the properties of models and how they can function in the classroom; (2) the Hobby project, a performance assessment for systems of equations and modeling; and (3) a particular piece of student work that demonstrates the potential power of uncertainty in mathematics classrooms. (A bibliography is included.)