The racial diversity of children in US public schools continues to increase while most teachers and school leaders are White. In addition, systemic racism, whitewashing of curricula, microaggressions, and deficit mindsets persist within schools across the country. These pervasive injustices that plague the student experiences of children of the Global Majority must be addressed with focused, sustained intention. This study offers social justice school leadership as an effective strategy to dismantle oppressive approaches to schooling. Specifically, it explores how social justice-oriented school leaders set the conditions for impactful, sustained staff development in social justice practice. By employing multiple case study methodology, the experiences of leaders within two New York City public middle schools that have established commitments to culturally responsive/relevant teaching (CR/RT) will be explored. Semi-structured interviews were used to uncover how school leaders leveraged both adaptive and technical leadership to enact school-wide efforts to embed CR/RT into instructional practice. Analysis was built on an existing framework to identify specific leadership roles that best support impactful social justice professional development over time. This study seeks to understand frequently overlooked aspects of this topic by delving into mindsets and actions, acknowledging both formal and informal school leadership and how such efforts play out within multiracial staff. This dissertation is available in open access at AURA (https://aura.antioch.edu) and OhioLINK ETD Center (https://etd.ohiolink.edu). [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.]