There has been increased interest in the transformation of post-secondary level instructional practices in STEM from more traditional to evidence-based practices that are more aligned with how learning occurs. Research has shown that instructional practices are linked to student learning outcomes even when content is unchanged; therefore, incorporating evidence-based practices into the classroom represents an area worthy of focus and resources. Problem-based learning (PBL) is an inquiry-oriented instructional strategy wherein students answer ill-structured real world problems through collaboration, research, experimentation, and trial and error. The success or failure of an inquiry-oriented laboratory session depends in large part on the practices of the instructor. The work presented here focuses on the instructional practices of chemistry graduate teaching assistants (GTAs), who over the course of a semester, taught both expository/ demonstration and inquiry laboratory sessions. Upon comparing GTA discourse across inquiry and expository/demonstration settings, three assertions were generated: (a) there was an apparent relationship between the instructional mode (expository/demonstration versus inquiry) and the structure of the classroom discourse employed by GTAs, (b) patterns in classroom discourse repeated within given instructional modes, even when the nature of content being covered varied widely, and (c) patterns in classroom discourse observed in inquiry labs exemplified a constructivist learning environment and were achieved with minimal intervention.