Recent curriculum design projects have attempted to engage students in authentic science learning experiences in which students engage in inquiry-based research projects about questions of interest to them. Such a pedagogical and curricular approach seems an ideal space in which to construct what Lee and Fradd referred to as instructional congruence. It is, however, also a space in which the everyday language and literacy practices of young people intersect with the learning of scientific and classroom practices, thus suggesting that project-based pedagogy has the potential for conflict or confusion. In this article, we explore the discursive demands of project-based pedagogy for seventh-grade students from non-mainstream backgrounds as they enact established project curricula. We document competing Discourses in one project-based classroom and illustrate how those Discourses conflict with one another through the various texts and forms of representation used in the classroom and curriculum. Possibilities are offered for reconstructing this classroom practice to build congruent third spaces in which the different Discourses and knowledges of the discipline, classroom, and students' lives are brought together to enhance science learning and scientific literacy. © 2001 John Wiley & Sons, Inc. J Res Sci Teach 38: 469–498, 2001