In the Republic of Ireland, school leadership policy adopts a distributed leadership model nationally. Given that this is a relatively recent policy development, research conducted on distributed leadership to date has highlighted that there are particular challenges for school leaders in enacting this model in practice and, more significantly, that principals have signalled their need for further leadership development in its enactment. In this study, we contribute to the growing national research on this leadership model. We chart the development of this policy and, drawing on primary school principals' perspectives, also explore opportunities and challenges in this context at school and system levels, illustrated richly through two participant vignettes and more generally in the discussion. We argue that constructive-developmental theory, a theory that acknowledges developmental diversity and richly theorises professional growth and development, offers school and system leaders a nuanced, differentiated, and transformative approach through which leadership development activities are led at school and system levels can support principals to enact distributed leadership in practice. We conclude by describing developmental supports for leaders and considerations for system leaders and policymakers, which are also likely to be of interest beyond the Irish context given the rise of distributed leadership internationally.