The National Council of Teachers of Mathematics (NCTM) vision for mathematics education is to provide every student with high-quality instruction from highly effective teachers. Achieving this goal requires a solid mathematics curriculum, competent and experienced teachers who can integrate instruction with assessment, classrooms with the proper tools and technology, and a commitment to both equity and excellence (Barajas-Lopez & Larnell, 2019). Decline in mathematics scores in the 2022 National Assessment of Educational Progress (NAEP) is cause for systemic change in how we implement these conditions. In this changing world, mathematical competence opens doors to successful futures. Disparities between the cultural, ethnic, and racial backgrounds of the majority of teachers and their students demonstrate the need for culturally relevant pedagogy in mathematics education today. This dissertation presents findings from a study that examined the relationship between teachers' mathematical instructional practices and the student achievement scores on a common assessment. A classroom observational instrument was used to measure the extent to which students experienced evidenced-based instruction in the classroom. Five categories were observed and rated according to the level of intellectual support that they experienced, depth of knowledge and understanding, mathematical analysis, mathematical discourse and communication, and student engagement. The findings of this study indicate that the instructional practices that included high levels of depth of knowledge and understanding and student engagement were significantly related to the students' common assessment scores. It was also noted that the overall Culturally Relevant Pedagogy (CRP) rating for teachers was significantly related to students' achievement scores on the common assessment. [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://www.proquest.com/en-US/products/dissertations/individuals.shtml.]