The Making Science project is developing, in collaboration with scientists and teachers, ecosystems-focused instructional materials that use sensor data and technology to help second and third graders become more proficient at data modeling and scientific argumentation. The major goals of the project are twofold: (1) provide elementary school teachers with a research-based curriculum that engages students in exploring and visualizing environmental data and using the data to construct scientific arguments that answer questions of interest, and (2) contribute to the cognitive development literature on children's ideas about and abilities for scientific argumentation. The project is advancing our understanding of cognitive development in young children and informing our thinking about learning progressions that involve the collection and use of data. The project addresses two of NSF's grand challenges--improving elementary education and introducing cutting-edge science into elementary school classrooms.