With the goal of producing scientifically literate citizens who are able to make informed decisions and reason critically when science intersects with their everyday lives, the National Research Council (NRC) has produced two recent documents that call for a new approach to K-12 science education that is based on scientific practices, crosscutting concepts, and disciplinary core ideas. These documents will potentially influence future state standards and K-12 curricula. Teachers will need support in order to teach science using a practices based approach, particularly if they do not have strong science backgrounds, which is often the case with elementary teachers. This study investigates one cohort (n = 19) of preservice elementary teachers' ideas about scientific practices, as developed in a one-semester elementary science teaching methods course. The course focused on eight particular scientific practices, as defined by the National Research Council's A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas (2012). Participants' written reflections, lesson plans and annotated teaching videos were analyzed in fine detail to better understand their ideas about what it means to engage in each of the practices. The findings suggest that preservice elementary teachers hold promising ideas about scientific practices (such as an emphasis on argumentation and communication between scientists, critical thinking, and answering and asking questions as the goal of science) as well as problematic ideas (including confusion over the purpose of modeling and the process of analysis, and conflating argumentation and explanation building). These results highlight the strengths and limitations of using the Framework (NRC 2012) as an instructional text and the difficulties of differentiating between preservice teachers' content knowledge about doing the practices and their pedagogical knowledge about teaching the practices.