Social capital has recently emerged as an effective approach to rethink schools as wider learning ecosystems where students, teachers and families have greater access to learning resources through social interaction. Literature has not provided research-based assessment tools that document school leaders' abilities to weave social relationships between actors within the school and across the community. This paper presents an international experts' validation of the SchoolWeavers Tool, an online resource that supports school leaders to assess the health and potential of their school ecosystem and provides meaningful feedback to weave social and professional capital and lift learning opportunities and educational goals. Theoretical validation was conducted in the first round by 15 experts from 8 countries with prior experience in network leadership in education, and in the second round, with 54 school actors from the same 8 countries. The final model provides an internationally validated tool that supports school leaders' capacities to improve collective effectiveness, internal and external collaboration, innovation and equity. Furthermore, the Tool creates research opportunities by allowing school leaders and researchers to collaborate and support systemic impact and sustainable improvement.