In teaching laboratories, scientific reasoning and argumentation are often taught in concert so students are provided opportunities to formulate a more nuanced understanding of science-as-practice and science as a social epistemology. Given recent calls to attend to the social aspects of science, we used Critical Contextual Empiricism, a social epistemology of science, as a framework for examining what features of a scientific community emerge in the introductory biology lab. In a case study of six graduate teaching assistants (GTAs), we explored how GTAs encouraged epistemic agency that encouraged their student’s efforts at knowledge construction in a community by collecting multiple data sources (e.g. audio recordings, students written work, focus group interviews) over a four-week sequence. Data analysis strategies were inductive, as a series of initial and focused coding were applied to select exchanges garnered from within the lab. Comparative analysis identified common occurrences across each respective case, which then revealed three overarching themes. We intended for GTAs to readily encourage epistemic agency to their students so insights regarding the social nature of knowledge production could be experienced and discussed. When epistemic shifts did occur, GTAs executed discursive moves targeting students’ experimental design practices (e.g. defining the dependent variable). Conversely, student’s efforts were also de-legitimized as GTAs provided specific directives to follow when challenges emerged for students. Finally, GTAs struggled to create a genuine community that modeled exemplary science-as-practice in the lab. Implications discuss how GTAs likely require more targeted support if community-driven learning is going to be successful in these uniquely challenging settings. Finally, working with non-science majors adds an additional layer of importance here given these lab-based experiences are limited and understanding the community’s role in generating scientific knowledge is a key component of being scientifically literate.