Conceptual change is among the most popular, contemporary theories for describing meaningful learning. Different theories of conceptual change describe the reorganization of conceptual frameworks that results from different forms of activity. I argue that learners’ mental models or personal theories resulting from conceptual change are most acutely affected by model-based reasoning. Further, model-based reasoning is fostered by learner construction of qualitative and quantitative models of the content or phenomena they are studying using technology-based modeling tools. Model building is a powerful strategy for engaging, supporting, and assessing conceptual change in learners because these models scaffold and externalize internal, mental models by providing multiple formalisms for representing conceptual understanding and change. Building models of domain content, problems, systems, experiences, or thinking processes using different representational formalisms represent different kinds of conceptual understanding that foster different kinds of conceptual change.