Becoming a teacher involves a continual process of identity development and negotiation. Expectations and norms for particular pedagogies impact and inform this development. In inquiry based classes, instructors are expected to act as learning facilitators rather than information providers. For novice inquiry instructors, developing a teacher identity may be fraught with contradictions. Inquiry-based learning approaches have been widely adopted in university biology laboratory courses. Teaching assistants (TAs) teach the majority of these labs. Despite TAs' importance in university science instruction, we know little about their teacher identity development. This study analyzes interviews and written reflections to explore how teaching science as inquiry figures into TAs' teacher identity formation. Through five case studies, the study characterizes the trajectories of TAs who made or did not make inquiry teaching practices their own. Most TAs made progress toward developing an inquiry-oriented teacher identity by shifting their focus to student learning. These TAs came to see their students as doing science rather than simply participating in a lab class. Findings also highlight beliefs that conflict with inquiry practices in order to inform strategies to support TAs' changing conceptions about science teaching and the development of inquiry teacher identities.