This paper takes an embodied and extended cognition perspective to ER integration – a cognitive process through which a learner integrates external representations (ERs) in a domain, with her internal (mental) model, as she interacts with, uses, understands and transforms between those ERs. In the paper, I argue for a theoretical as well as empirical shift in future investigations of ER integration, by proposing a model of cognitive mechanisms underlying the process, based on recent advances in extended and embodied cognition. I present this new model in contrast to the still dominant classical cognitivist (information processing) approaches to ER integration, and the educational technology intervention designs such approaches inspire. I then exemplify this distinction between the information processing model and the new model through a case of arithmetic problem solving. Corroborative neuroscience evidence presented in relation to this case shows that (bodily action or) sensorimotor mechanisms are critical to ER integration and learning, further supporting the new model. Finally, as educational implications of the new model, I demonstrate the need for: (i) re-viewing the development of ER integration and expertise also as a fine-tuning process of the cognitive agent’s action or sensorimotor system, and (ii) a shift of focus in new-media intervention design principles based on the newer understanding of ER integration in science, technology, engineering and mathematics.