Cross-divisional collaboration represents a specialized form of vertical sharing occurring when school personnel discuss issues of teaching and learning with their peers across traditional divisional boundaries (i.e., elementary, middle, and high school). Recent empirical evidence highlighted the benefits of cross-divisional collaboration, asserting the practice could deepen educators’ understandings of curricula, strengthen students’ overall academic bases, and even build respect between cross-divisional colleagues. Unfortunately, due to scheduling and physical site limitations, the previous works announcing cross-divisional collaboration’s potential relied on external interventions to facilitate peer interactions, leaving it largely unexplained how school leaders could implement and sustain this specific form of sharing. As flexible organizations frequently situating multiple divisions on a single campus site, K-12 independent schools offered an ideal arena for this study to build on the extant literature and examine the mechanisms and benefits of cross-divisional collaboration in their real-world contexts. Specifically, leveraging social capital theory and distributed leadership theory, this work carried out a multiple-case study involving formal and informal leaders at two independent schools identified as exemplars of cross-divisional practice. To begin addressing the recognized gap in the literature, this investigation collected interview, document, and field note data, to reveal how independent school leaders sustained cross-divisional collaboration. Due to a lack of existing research involving K-12 independent schools, this work also explored the perceived outcomes of cross-divisional practice within these unique educational organizations. Resulting from a cross-case synthesis between this study’s two site schools, the findings supported addressing barriers, establishing a constructive culture, and investing in relationships as essential leadership activities related to the facilitation of cross-divisional collaboration. Furthermore, the participants in this work indicated their school’s cross-divisional practice led to deeper connection and meaningful improvement in their school communities. In addition to informing independent school practitioners, these results begin to address the previous gap in the literature and serve to inform future works.