This paper documents the rise and fall of a micro-learning region in Philadelphia. The central actors in this region are undocumented Mexican immigrants who until recently were able to draw on the intensity of their workplace interactions and their heterodox knowledge to produce new and innovative building techniques in the city's residential construction. The new knowledge they developed was primarily tacit. More significantly, the learning practices through which immigrant workers developed skills and innovated new techniques were also heavily tacit. Because these practices were never made formal and were never made explicit, they remained invisible and difficult to defend. With the housing-market collapse and subsequent decline in housing renovation in the south-center region of Philadelphia, this tacit knowledge, and the practices that gave it shape and significance, are no longer easily accessible. We draw on this case to demonstrate the importance of access to the political and economic resources to turn learning practices into visible structured institutions that protect knowledge and skill. Whether or not the practices that support knowledge development are themselves made explicit can determine whether the knowledge they produce becomes an innovation that is recognized and adopted or whether it remains confined to a set of ephemeral practices that exist only so long as they are being enacted.