While research on Irish-medium immersion education (IME) has heralded benefits such as cognitive skills, academic achievement and language and literacy development, many studies have also identified challenges to its successful implementation. Immersion-specific research-validated tools can help school leaders navigate the school self-evaluation journey, critically review and evaluate the quality of aspects of their school's provision and plan for improvement. This paper reports on one theme, leadership, from a larger study, Quality indicators of best practice in Irish-medium immersion (Ó Ceallaigh and Ní Shéaghdha, 2017). Qualitative in nature, the study was guided by the following research question: What are IME educators' perceptions of best practices in IME?. The study explored 120 IME educators' perceptions of best practice in IME to inform the development of IME quality indicators. Individual interviews and focus group interviews were utilised to collect data. Data analysis revealed particular themes related to best IME leadership practices. Findings in turn informed the design of an evidence-informed school self-evaluation tool for IME settings. The various functions of the tool will be explored with a particular emphasis on building teaching and leadership capacity in IME through the school self-evaluation process.