Inquiry-style laboratory courses, in which students engage in open-ended projects rather than a prescribed set of experimental steps (“cookbooks”), are becoming increasingly popular at the undergraduate level. Reformed curricula require reforms in training teachers; in the case of large universities, laboratory instructors are typically graduate teaching assistants (TAs). The General Chemistry Laboratory courses at a large, public, research-intensive university in the Midwestern region of the United States recently underwent a transformation from a “cookbook” to a project-based lab, and despite efforts to improve training, TAs continue to express difficulty teaching the course. To determine the source of these difficulties, we conducted multiple video observations and semi-structured interviews with seven TAs throughout one semester. We report TAs’ beliefs about what is expected of them, their philosophical alignment to perceived expectations, and a comparison of the Lab Coordinator's expectations to TAs’ actual teaching practices. We found that the TAs generally agreed with behaviors they were expected to perform, but responses to actions they were not supposed to do indicated that they were unsure of what the Lab Coordinator expected and personally believed that an ideal TA would perform those actions. This work highlights a need to clearly communicate the aims and expectations in a course and the rationale for those choices.