This dissertation looks at the impact of instructional leadership in mathematics teaching on teachers at various stages in their careers. Using a case study methodology, the researcher explores the nuanced needs and effective strategies for beginning, mid-career, and established teachers. Peer instructional leaders provided data that involved a mix of qualitative methods, including surveys, interviews, and questionnaires, targeting five assistant principals selected randomly from diverse school environments. The study identifies common themes and differences in instructional approaches, highlighting how strategies vary and overlap across different career stages. Analysis gives insights into the practical application of leadership in educational settings, emphasizing the role of instructional leaders in teachers' professional growth and improving student learning outcomes in mathematics. The findings suggest actionable implications for future professional development and leadership practices. This research offers a snapshot of current practices and potential areas for improvement in math instructional leadership. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]