Representations support learning and instruction in many ways. Two key aspects of representations are discussed in this paper. First we briefly review the research literature about cognition and processing internal mental models. The emphasis is on the role that mental models play in critical reasoning and problem solving. We then present a theoretically-grounded rationale for taking internal mental representations into account when designing and implementing support for learning. The emphasis is on interaction with meaningful problems. Lastly, we present research that has led to a conceptual framework for integrating models into learning environments that includes technologies for formative assessment and motivation.