Within the lager landscape of algebra, we focus here on an aspect of algebra that many mathematics educators refer to as algebraic reasoning (e.g., Kaput 1999), which includes using arithmetic for generalizing, working with patterns to describe functional relationships, and modeling as a way to formalizing generalizations. Algebraic reasoning has begun to play an increasingly important role in US mathematics instruction, as evidentced by its emphasis in serveral grade levels of the Common core standards (Common Core State Standards Initiative 2010). Furthermore, the exploration and modeling of data that lie at the core of algebraic reasoning are central to the work of scientists, engineers, and other STEM professionals (Hoyles et al. 2010). In many middle grades mathematics classrooms, algebraic reasoning is instantiated through the identification, justification, and generalization of numerical patterns in given or generated data.