The present paper proposes a Dynamic Model of Social Structures as a model of language choice which highlights and synthesizes two significant themes repeated throughout the history of language choice research: agency and function. This model stems from ecological frameworks advanced in the fields of language planning (Hornberger, 2002) and language learning (Lam, 2007). Central to the model is the notion of language as a social structure (Gafaranga, 2005) among infinite other social structures (e.g., broader society, social network, local context, and individual linguistic behaviors). The Dynamic Model of Social Structures integrates the concept of agency and function in demonstrating how social structures influence one another and how individuals enact social identities through the discursive functions of their individual language choices. Research from a primary school Spanish immersion program in Arizona illustrates the application of this model and its value as a framework especially suited for classroom language choice research.