Advancing Professional Development of Transformative Elementary Mathematics Specialists (TEMS) addresses the critical need for improved mathematics education of elementary teachers and their students. The project will achieve this goal by preparing and supporting 60 Elementary Mathematics Specialists (EMSs) who are highly effective mathematics teachers and teacher leaders. The program provides these EMSs with professional development grounded in research-informed practices and focuses on refinement of an existing program. The project aims to develop ambitious, responsive mathematics instruction and to provide high-quality coaching to teacher candidates and novice teachers. With a renewed call for mathematics specialists to be in every elementary school, they need specialized research-based preparation to be transformative and impactful in their settings. The program aims to make needed contributions to the knowledge base on elementary mathematics specialist preparation through evaluating the effectiveness of the professional development program and iteratively leveraging informed advice and evidence-based feedback to improve the model. Dissemination of the refined program resources is a critical component and will include sharing materials for other elementary mathematics specialist program designers. The research and evaluation will include both formative and summative components. The formative research will help support networked improvement communities to identify