Purpose: Despite growing recognition of the importance of cross-system collaboration, there remains limited scholarship on policies promoting cross-system school partnerships. This paper examines an underexplored policy initiative—the Sister School Scheme—implemented between schools in Hong Kong and Chinese mainland since 2004. We trace the development trajectory of this initiative and analyze its implications for cross-border educational collaboration. Design/Approach/Methods: The study primarily relies on official policy documents issued by national, provincial, and local governments between 2004 and 2023, as well as speeches by politicians reported in media sources. Data analysis involved a comprehensive review and comparison of these texts to identify patterns, recurring themes, and discursive shifts over time. Findings: This preliminary analysis reveals that, since the Scheme's launch, its scope and focus have been significantly shaped by major social events occurring at critical historical junctures. In addition, the policy has served as a strategic tool to foster cross-border educational exchange and collaboration between schools in Hong Kong and Chinese mainland. Originality/Value: This study contributes original insights by offering the first longitudinal policy analysis of the Sister School Scheme, a relatively overlooked initiative in cross-border education research. It adds value by uncovering how educational policy evolves in response to broader social dynamics, and by shedding light on the role of school partnerships in fostering cross-system collaboration. Copyright © 2025 The Author(s).