The DAT-CROSS project aims to address the lack of valid assessments that probe science-based crosscutting concepts as well as the lack of tools (learning progressions) to guide instruction around these concepts. The project's first aim is to develop and validate computer-based summative assessments that focus on the crosscutting concepts of systems and system models and structure/function. Consistent with the NGSS, the assessments developed from this project will also probe the integration of these crosscutting concepts with two different disciplinary core ideas as well as different science practices. At the same time, we will hypothesize and begin to validate LPs for the targeted crosscutting concepts of systems thinking and structure/function. The results of our project should inform future nationwide assessments and state standardized assessments on crosscutting concepts as well as create validated learning progressions on students’ mastery of these concepts, to help guide teachers’ instructional design.