With the reform of the Irish Junior Cycle since 2015, the discourse around school ethos in Ireland is gaining momentum. This paper explores one particular quality of Catholic ethos highlighted by Pope Francis since the beginning of his papacy -- the quality of mercy. His articulation of mercy as core to all Catholic ministry reminds Catholic schools of their role as warmly inclusive communities that enable all to flourish, and their particular responsibility to those who are most in need. However, it can be difficult for many in the English-speaking world to get a sense of what mercy ("misericordiae") actually means. This paper attempts to break open the papal understanding of mercy and the significance of mercy for Catholic schools today. Using examples from three schools, it illustrates some characteristics of a merciful Catholic school community. The focus of the paper is second level school, although the principles may be of interest to those working with other education sectors.