One aim of inquiry activities in science education is to promote students’ participation in the practices used to build scientific knowledge by providing opportunities to engage in scientific discourse. However, many factors influence the actual outcomes and effect on students’ learning when using inquiry materials. In this study, discourse from two physical chemistry classrooms using the Process‐Oriented Guided Inquiry Learning (POGIL) approach was analyzed using a lens of scientific argumentation. Analysis of the complexity of reasoning in students’ arguments using a learning progression on chemical thinking indicated that students did not employ very complex reasoning to construct arguments. To explain the distribution of reasoning observed, a separate analysis of the curricular materials was performed using the Task Analysis Guide for Science (TAGS). Results indicate a relationship between the task's targeted scientific practice and how students used evidence in their arguments as well as between the task's cognitive demand and the complexity of reasoning employed in arguments. Examples illustrating these relationships can be used to inform implications for design of inquiry materials, facilitation of classroom discourse, and future research. © 2017 Wiley Periodicals, Inc. J Res Sci Teach 9999:XX–XX, 2017