Public prekindergarten (pre-K) is increasingly common in U.S. public schools. The policy decision to house pre-K classrooms in public schools places pre-K teachers in a “borderland of practice,” where the separate worlds of the early childhood and K–12 systems collide. Borderland work has implications for pre-K teachers’ job satisfaction, professional identities, and sense of belonging. Focus of Study: The purpose of this study was to understand how pre-K borderlands come to be constituted and how features of the borderland shape the lived experiences of school-based pre-K teachers. The context for the study was Michigan’s state-funded pre-K program, Great Start Readiness Program. We drew on scholarship in border studies to conceptualize the pre-K borderland as the space around the borders separating early childhood education (ECE) and K–12 systems. We sought to understand how the pre-K borderland was shaped by policies and policy actors and the implications this had for pre-K teachers’ work experiences and well-being. (author abstract)