The purpose of this qualitative phenomenological study was to explore Pennsylvania public high school principals' leadership of grading practices reform and how that leadership was influenced by enabling and constraining factors within schools' cultures and communities. The analysis of the accounts of the lived experiences of 10 principals produced seven experiential themes that provided insight into what drove the participants to pursue grading reform within their schools and how participants made sense of the factors that enabled and constrained their leadership. This study found that principals were driven to pursue grading reforms by concerns about a lack of humanity in the grading process and concerns about the validity and reliability of grades. However, principals were constrained by students' and parents' comfort and familiarity with the current system, concerns about the impact of changes to grading on the college admissions process, and the existence of a "this too shall pass" culture among teachers. Principals in this study approached grading reform by creating cultures of trust and transparency within their schools and supporting the work of teacher pilot groups to change grading practices. [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.]