Purpose: This study explores how secondary school leaders make sense of the transition to high school and how their sensemaking informs their decisions and practices to sup-port their students during this transition. Additionally, this study will examine the relation-ship between what secondary school leaders believe to be critical practices to support students during this period and what practices these leaders implement. Any discrepancy between the two constructs (i.e., belief and action), will be studied to determine what factors serve to moderate the relationship. Research Questions: (1) How do secondary school leaders make sense of the transition to high school?; (2) What practices do secondary school leaders consider integral to supporting students in the transition to high school?; (3) What challenges do secondary school leaders face in supporting students during the transition to high school? Theoretical Framework: The study is theoretically grounded in sensemaking. While there is no single definition for sensemaking, it can be reasonably codified as a response to stimuli, involving the creation of meaning through synthesis of multiple constructs, that is recursive in nature and can be both an individual and collective experience. Methods: This single-case embedded case study was conducted in an urban school district in the southeast-ern United States, including the principals of the six district high schools. Data collection in-cluded two semi-structured individual interviews, document review, and analysis of archival data of the case and subunits. Data were analyzed using In Vivo and Values Coding, followed by Focused and Axial Coding to identify emergent themes. Findings: Findings: The study find-ings yielded four axes that capture how the participants make sense of the transition to high school, the practices they consider integral to supporting students during the transition to high school, the practices they currently use to support their ninth grade students, and the internal and external chal-lenges they encounter in their efforts to support the transition to high school. Each axis is com-prised of six components. Implications: This study addresses a gap in the literature about how secondary school leaders’ sensemaking of the transition to high school informs what they believe to be integral practices to support students during this phenomenon and what practices they choose to, or can, implement within their school contexts. This study allows secondary educational leaders to consider their own sensemaking of the transition to high school, while also providing potentially valuable insight into the practices they can employ within their contexts to support their students during this critical phase of their school experience.