With support from the NSF Improving Undergraduate STEM Education Program: Education and Human Resources (IUSE: EHR), this project aims to serve the national interest by improving math fluency in introductory physics courses. The goal is to use research-based principles, together with methods from cognitive psychology and education research, to develop, implement, and assess a set of practice assignments called Math Practice. Math Practice is based on Essential Skills, an existing online platform used at Ohio State University. The initial scope of this project is to advance knowledge about how to address students' difficulties with math skills that are needed for success in introductory physics courses. This initial work will involve the 15,000 students in introductory physics courses at the target schools. However, because this intervention is both low-cost and logistically simple to implement, it could potentially improve performance and retention of the 500,000 students enrolled each year in physics classes nationwide. Furthermore, although the Math Practice application will be designed to help all students, it is likely to especially help underprepared students succeed and continue in physics courses. <br/><br/>The design of this proposed intervention is based on well-established research-based learning methods, including spaced and interleaved mastery practice with immediate feedback. This method is expected to automate and thereby reduce the cognitive load involved in applying basic math procedures in physics. Reducing cognitive load is important since physics tends to have complex, perceptually rich notation and contexts. The experimental design will include control conditions and "A/B testing" to explore optimal practice tasks and formats, such as comparison of alternative solutions and combinations of generic and context-rich format practice. The assessments will include validated math instruments, course performance, and motivational survey scales. These assessments will be used for iterative improvement of materials, investigation of areas of student difficulty, and investigation of potentially important student-level factors of performance and motivation. As a result, the practice tasks and assignment design will have a strong empirical and theoretical basis. Further, this project is expected to advance knowledge about student difficulties with essential math skills and the mechanisms underlying these difficulties, in an introductory physics context. In addition, it is expected to advance knowledge of the effectiveness of several specific kinds of empirically and theoretically promising math practice tasks. Finally, the project is expected to determine the extent to which student characteristics and motivations interact with this intervention. Thus, it will potentially provide information about the mechanisms of the difficulties and additional avenues for productive interventions. Given that math is essential in all STEM disciplines, the information learned in this project could potentially extend to all of STEM education. For example, the difficulties students have with symbolic notation in introductory physics are also likely to be encountered in other areas of STEM. The NSF IUSE: EHR Program supports research and development projects to improve the effectiveness of STEM education for all students. Through the Engaged Student Learning track, the program supports the creation, exploration, and implementation of promising practices and tools.<br/><br/>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.