For nearly three decades, mathematics research has indicated the need for high-quality mathematics instruction including both ambitious and equitable practices, as well as continuous, innovative learning opportunities for educators. Teaching practices and standards for mathematical practice have been identified to provide guidance. While research connects effective professional development (PD) to improved instructional practices, there is a need for additional research on the role mathematics specialists play in developing and sustaining PDs. This qualitative case study examined the multiple roles of a specialist while laying the foundational components for a coordinated PD system to improve and strengthen mathematics teaching and learning in elementary classrooms. The PD efforts included the implementation of a teacher subsystem where a specialist led all components consisting of pull-out PD, mathematics coaching, collaborative time, and teacher networks. This study took place at a rural, pre-K through fourth-grade school in a southeastern state. Analysis of the data identified the specialist's key roles in each component of the teacher subsystem. The results indicated that the development and implementation of a teacher subsystem impacts the overall effectiveness of PD. Findings serve as a foundation for specialists to design and implement coordinated efforts that can have positive impacts on the teaching and learning of mathematics.