For the past three decades, mathematics research has indicated the need for high quality mathematics instruction that includes both ambitious and equitable practices, as well as continuous, innovative learning opportunities for educators. While research connects effective professional development to improved instructional practices, there is still a need for additional research on what this professional development should entail for elementary mathematics classrooms. This study sought to determine how one school coordinates its professional development efforts, with respect to fourth grade, in mathematics instruction. The qualitative case study gathered information and experiences from six participants. The study took place at a rural, pre- K through fourth grade school in east Alabama. The study collected data on the specific opportunities afforded to teachers throughout one semester of focused efforts on mathematics instruction and on the impact of the efforts had on classroom instructional practices. All professional development efforts centered on the use of mathematical number talks within the elementary classroom setting. Analysis of the data revealed that while the development of a strong focus and overall goal for professional development opportunities is necessary, it is also important to ensure that all efforts align in order to meet the overall goal. Data also showed the importance of developing a strong teacher subsystem, complete with professional development opportunities, instructional coaching, teacher collaboration, and teacher networks. The results indicate that number talks implemented in elementary mathematics classrooms can have positive impacts on instructional practices. The results also indicate that development and implementation of a teacher subsystem impacts the effectiveness of professional development reform efforts. Findings from this study can be used by administrators, instructional coaches, or those involved with coordinating professional development efforts. Future research could apply the same organizational structure over a longer period of time with a larger number of participants. Additional research on a larger scale is needed to further determine the impact of number talk implementation on teachers’ instructional practices.