The purpose of this concluding chapter is to provide a first international comparison and assessment of the state of the art of system leadership in OECD countries. The chapter summarises what the research is saying about system leadership, and examines the actual practices in which school leaders are collaborating and working together with other schools in five different countries. The analysis reveals the benefits: leadership capacity building, rationalisation of resources, improved co-operation, a greater distribution of leadership within schools and improving school outcomes. It also presents the challenges to sustainability of system leadership: the difficulty of marrying co-operation and competition; the need to recognise and support distributed leadership within the school; the need to identify, recruit, develop and reward system leaders; and the need to find the right institutional support for the practice. The authors propose that eventually, the collective sharing of skills, expertise and experience will create richer and more sustainable opportunities for school transformation than can be provided by isolated institutions. But attaining this future demands that we give school leaders more possibilities in taking the lead.