The Multiple Literacies in Project-Based Learning (PBL) project will design, develop and test rigorous interdisciplinary project-based learning curricula for the upper elementary grades. Lessons will require sense making through the application of science ideas and practices, language literacy, mathematical thinking and technology tools. The exploration of culturally and personally relevant driving questions will support student learning. In doing so, these PBL curricula will promote access to and ownership of knowledge for diverse learners. The project, in addition to designing, developing and testing curriculum materials, will result in a model for how to develop effective interdisciplinary PBL elementary curricula. As a design-based initiative, materials will be developed iteratively and vetted by teachers, administrators, and students throughout the five-year project. Partnering schools will reside in under-resourced communities that serve diverse learners. In Years 1-2, teaching experiments with at least three teachers in each of grades three and four (approximately 75 to 90 students per grade) will enhance the development of unit designs. In Years 2-3, these teachers will pilot units, providing further information regarding the sequencing, clarity and effectiveness of learning tasks, how teachers enact the materials, and the design of assessments that will reveal learning outcomes. Field-testing in Years 3-5 with ten PBL classrooms (approximately 250 to 300 students) and 5 comparison classrooms (approximately 125 to 150 students) per grade will establish promising evidence of effectiveness of the curricula. In Year 5, a study with 20 PBL classrooms and 20 comparison classrooms will provide “gold-standard” evidence of effectiveness of the third-grade materials. Effectiveness will be evaluated based on productive shifts in teacher practice; improved student performance on science, literacy and mathematics outcomes; increased student efficacy and metacognition in science learning and language use; and greater student motivation and engagement to explore science using scientific practices, language and mathematics.