In this paper, we revisit a long-running conversation about situated learning and the design of environments for disciplinary engagement. Throughout the 1970s and 1980s, scholars advanced an anthropological critique of the then-dominant acquisitionist paradigm of formal schooling with a situated view focused on membership in communities and participation in practices. The critique led to a practice turn in education and a consensus model for reform-oriented school classrooms as orchestrated practice fields where students engage in disciplinary practices within a structured environment. Questions remain, however, about the nature of the practices and communities that this model engenders. We join this conversation through an anthropological investigation of a self-organized group of teachers who gather outside of school hours to engage in collaborative mathematical activity. Participants have the flexibility to conduct their mathematical activity however they want; yet as we show, they tend to reproduce a practice field resembling a reform-oriented school mathematics classroom. This may seem unremarkable, even desirable for many reformers. However, assuming that teachers can or should only replicate practice fields when doing mathematics may be selling them short. Our findings suggest a durability and invisibility to practice fields that may be limiting the possibilities for the production of novel learning communities within schools.