“…To this end, we use the term mathematical model (i.e., model) to refer to "material, visual sketches, paradigmatic situations, schemes, diagrams, and even symbols" that help students manage, document, communicate, or interpret mathematical ideas and phenomena [27] (p. 13). Much of the research with integers supports the use of the number line model [10,28] and chip model [29], though some researchers have also described models such as elevators [13,22,24]. Research examining textbooks and curricula in the domain of integer operations [30] has shown the use of number lines, chip models, and contexts as models for dealing with integer operations.…”