Each person learning a second or foreign language faces a unique developmental path. Individual learning trajectories have been obscured, however, by the search for “best practices” in second language educational research and praxis (Edge & Richards, 1998). This one-size-fits-all view has been further reinforced by a predominant cognitivist tradition, which orients to cognition mainly through mechanical and input and output processing, or a “mind as machine” metaphor (Boden, 2006). My dissertation aims to offer an alternative to this tradition. In my dissertation, I introduce a music-based intervention designed to develop students’ pronunciation (speech rhythm) in a U.S. college-level English as a second language classroom. The intervention draws heavily on the rhythmic properties of rap and other forms of popular music. Rather than contending solely with the binary question of whether the intervention works (or results in “best practices”), I use mixed methods to examine individual student outcomes through the lens of three major complex subsystems of second language development (Larsen-Freeman, 2011): ideological, interactional and speech production. I aim to demonstrate that students’ rich in-class interactional practices and ideological understandings of the (African American) language associated with the music in the intervention (and with my own Blackness as a teacher-researcher) reveal as much about their second language development as does an assessment of their speech rhythm production. Building on the premise that language learning is an endeavor that is not only cognitive in nature, but also social, my dissertation advocates for a much fuller contextualization of second language development and classroom practices.