As mobile devices become increasingly pervasive among youth, the gap between students with and without access to personal computers at home may soon be replaced by a new digital divide: between one set of informal ways of using those tools that are familiar, personally meaningful, and relevant to their out-of-school lives, and another set of uses in formal instruction contexts that has nothing in common with the first except hardware. Admittedly, learners' personal forms of digital activity can appear quite different from and even oppositional to productive, school-based activity, and to educational uses of the same devices. But the authors argue for a different perspective, namely that those informal digital practices may provide uniquely powerful resources around which to organize innovative and engaging instructional approaches. Many of the ways students are already using smartphones and other contemporary mobile computing devices correspond to core aspects of disciplinary practice in STEM (Science, Technology, Engineering and Mathematics) fields. The authors believe that leveraging the existing ways learners use digital devices as resources for organizing learning activities represents a particularly powerful approach to supporting student learning in STEM content areas. They discuss how schools can leverage the ways students are already using mobile digital devices to organize and support learning activities.