In STEM education, widely accepted teaching goals include not only the development of solid content knowledge but also the development of general scientific reasoning abilities that will enable students to successfully handle open-ended real-world tasks in future careers and design their own experiments to solve scientific, engineering, and social problems. It is often expected by teachers that consistent and rigorous content learning will help develop students' general reasoning abilities. However, research has shown that the content-rich style of STEM education made little impact on the development of students' scientific reasoning abilities. Research also indicates that inquiry based science instruction can promote scientific reasoning abilities and that the scientific reasoning skills of instructors can also significantly affect their ability to use inquiry methods effectively in science courses. In order to effectively implement inquiry based science curricula for students to develop science knowledge and scientific reasoning ability, good assessment tools are needed to evaluate the impact of the different inquiry based curricula. These assessment tools should be easily applied in large-scale applications and produce valid results for evaluating students' scientific reasoning abilities. Existing assessment instruments do not provide enough coverage on scientific reasoning. This project will build on existing resources to develop an assessment instrument and a knowledge base on scientific reasoning. The proposed research and development will include the development of a set of standardized assessment instruments on scientific reasoning, a knowledge base ranging from senior elementary school to undergraduate college illuminating the development of students' scientific reasoning, and a community website to archive, share, and disseminate the resources and to sustain future research and development in education that promotes scientific reasoning.