This project aims to serve the national interest by improving undergraduate student achievement in introductory STEM courses. It will do so by identifying classroom practices that enable a greater number of students to thrive in these courses. Whether or not a person completes a four-year undergraduate degree is a primary driver of income levels. Thus, barriers to earning degrees can present significant obstacles to socioeconomic mobility in the United States. One such barrier is successful completion of introductory STEM courses. Persistence in these courses varies even in STEM disciplines in which students from under-represented groups enter the major at the same rates as their majority peers. Persistence of students is affected by how their instructors teach. For example, incorporating active learning methods in introductory STEM courses can increase student achievement and lower performance gaps. However, not all implementations of active learning are equally effective for supporting these outcomes. A meta-analysis of over 46,000 students in a wide array of STEM courses compared student outcomes in lecture-based versus active learning classrooms. Active learning reduced achievement gaps in exam scores by an average of 40% and the gap in failure rates by 75%. Surprisingly, some active learning interventions widened achievement gaps, raising questions about why the variation exists. Findings from the literature point to two complementary elements of the classroom experience that are necessary to close achievement gaps: (1) an inclusive environment where all students believe they can be successful, which primes them to meaningfully engage; and (2) active learning that follows best practices for how people learn. This project team aims to identify and test the impact of specific elements of classroom culture and course design that effectively narrow achievement gaps.This project has three aims: (1) Generate an explanatory model of achievement gaps by identifying and measuring a set of critical elements for closing these gaps in 12 courses identified in a meta-analysis that either narrowed or widened achievement gaps; (2) Establish generalizability of critical elements on achievement gaps by training and validating a predictive model on a national sample of 40 additional introductory courses from a wide array of institution types; (3) Develop, evaluate, and promote a Practitioner’s Toolkit for Closing Achievement Gaps. This Toolkit will include instructor and student questionnaires that feed directly to a data processing application that fits the predictive model for unique classrooms. In addition, the Toolkit will include self-reflection activities to promote engagement with the personalized results of the predictive model and a guidebook for improvement that explains implementation of each critical element. Thus, this project intends to produce a novel set of tools that instructors can use to enhance student performance in higher education, helping to make a four-year degree attainable by all students. The tools developed by the project will be freely available online and disseminated through invited seminars, workshops, and presentations at national meetings. The NSF IUSE: EHR Program supports research and development projects to improve the effectiveness of STEM education for all students. Through the Institutional and Community Transformation track, the program supports efforts to transform and improve STEM education across institutions of higher education and disciplinary communities.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.