Recent accountability policies seek to "grade" teacher preparation programs by the teaching evaluations of their graduates. This article addresses the problematic nature of the linear thinking underlying such reforms by examining the construction of teaching practices of Mauro, a first-year secondary science teacher who taught environmental and earth sciences. Drawn from a larger data set, the study uses concepts from rhizomatics, a non-linear theory of thought and social activity, and elements of postmodern grounded theory. Despite holding key factors constant across the two subject area settings, differences in the ways the teacher, students, and contextual conditions worked together helped produce strikingly different teaching practices in each set of classes. This study provides evidence that enacting pre-professional learning is a complex undertaking shaped by the ways the elements present in the school setting work together, and, thus, teaching is a collectively negotiated activity. The author offers implications for teacher preparation practice and policy, advocating for an ontological turn in teacher education research that focuses on processes of teaching rather than outcomes alone.