One goal of project-based science is to promote the development of scientific discourse communities in classrooms. Holding rich high school scientific discussions is challenging, especially when the demands of content and norms of high school science pose challenges to their enactment. There is little research on how high school teachers enact scientific discussions using project-based science curricula, making the kinds of necessary embedded supports unclear. To address that gap in the research literature, this study analyzed curriculum supports and embedded educative features for the enactment of science discussions in one high school project-based science curriculum. Through a study of teacher enactment and a comparison of the curriculum discussion supports, we observed that while teachers increased their attempts to engage in inquiry-based discussion practices where supports were offered, they relied on heavily on traditional “recitation” formats, demonstrating that existing curricular supports were not developed enough to support dialogic classroom interactions. We hypothesize about conditions that may contribute to the pervasiveness of typical discourse practices in high school science discussions. We argue for expanded curricular discussion supports for teachers and design research on developing discussions in high school project-based science classrooms to examine how such supports are taken up, dismissed, or modified in practice. © 2009 Wiley Periodicals, Inc. Sci Ed94:395–427, 2010