In a school district in the Southwestern region of the United States, middle school music educators did not participate in district-wide initiatives to improve teacher assessment literacy, which encompasses the assessment knowledge and practices of teachers in support of student learning. The educators varied widely in their grading and assessment knowledge and practices. The purpose of this qualitative explanatory case study was to explore the middle school music educators' perspectives of their assessment knowledge and practices in the classroom and how they used assessments to evaluate students' knowledge and skills in music. Xu and Brown's teacher assessment literacy in practice framework underpinned this study. Semistructured interviews and assessment example documents from twelve licensed middle school music educators who taught band, choir, or orchestra were analyzed using a priori, open, and axial coding strategies to derive themes. Findings showed that participants assessed student musical performances by aligning the assessment purpose to the type of assessment and grading practices, and they used grading knowledge and feedback practices to improve student performance. Based on these findings, a white paper was developed with three recommendations for music educators and district leaders. Implementation of the recommendations may contribute to positive social change through the development of music teachers' assessment literacy, which could improve their teaching practice and increase student learning. [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.]