Over the past decade, I have conducted ethnographic research across academic and non-academic settings about what and how people know at work and about how they become experienced and competent practitioners as they begin to participate in workplaces. The common experience across all of these sites include an experienced abyss between what is taught and tested in formal schooling and the competencies that are required to be good at work. At the same time, tacit modes of learning were identified that allowed new practitioners in all these fields to become competent practitioners. Considerable transformations of practice and learning could be observed, among non-academic as well as among more academic professions , when (new and old) members engaged in the practice of reflection . In this chapter, I use practice theory and cultural-historical activity theory to articulate similarities and differences in school learning and learning on the job, and learning by implicit (tacit) and explicit modes. I focus in particular on the ways in which reflection on practice, generally mediated by some technology provides renderings that allowed a rejoining of theory and practice to occur.