This study, grounded in Senge’s change theory, investigates the role of teachers’ knowledge in achieving inclusive and equitable quality mathematics education for all students. Specifically, it examines teachers’ understanding of concept-based mathematics teaching and their knowledge of the Standards for Mathematical Practice (SMPs), revealing knowledge gaps that may impact educational equity. This study’s findings indicate that teachers’ familiarity with the SMPs and their understanding of concept-based mathematics teaching are limited, potentially restricting students’ access to rigorous mathematics education. Furthermore, many teachers equate solving real-world problems with having a conceptual understanding of mathematics—a misconception that may hinder their ability to promote rigorous mathematics education. To address these challenges, professional development initiatives are proposed for achieving the United Nations’ Sustainable Development Goal 4, that is, providing equitable, high-quality education. This study recommends a collaborative and continuous improvement approach to professional development that integrates Senge’s concepts of personal mastery and team learning to foster a shared learning culture. While focusing on the U.S. context, these findings have global relevance, suggesting that mathematics education leaders worldwide should assess the gaps among educational policies, resources, and teachers’ knowledge within their systems.