Mathematics specialists support the teaching and learning of K-12 mathematics and attend to school-based responsibilities and needs. This study examined the shifts in responsibilities of mathematics specialists during the COVID-19 pandemic to better-understand their current and potential future influence on mathematics teaching. An online survey was administered nationally to reveal how school-based mathematics specialists adapted their responsibilities in response to the changing school conditions. Responses from school-based mathematics specialists were analyzed using a mixed methods approach to capture self-reported shifts in responsibilities, as well as challenges and opportunities. Findings indicate that the school-based mathematics specialists were able to rapidly reprioritize their responsibilities in response to both teachers' professional learning and instructional needs. These findings illuminate the importance of mathematics specialists as school-based leaders who must continually navigate relationships and apply leadership knowledge and skills in novel ways to support shifts in mathematics teaching and learning.