The advantages and disadvantages of single-sex schooling continue to be a source of policy and public debate. Previous empirical evidence is somewhat ambiguous, with some studies finding a positive impact of single-sex schooling on education achievement and others finding no differences across school types. The relationship between single-sex schooling on academic outcomes is typically problematic to examine, as in most countries single-sex schools are selective and the numbers attending them are relatively small. In Ireland, a high proportion of secondary school children ([approximately] 1/3) attend a single-sex school. In addition, these schools are largely state-funded and non-selective but differing in composition compared to mixed-sex schools. For this reason, the Irish educational system provides an interesting setting for exploring the outcomes of single-sex schooling. In this context, this study utilises the 2018 PISA data for Ireland to examine the relationship between single-sex education and mathematics, reading and science literacy performance for boys and girls, respectively, as well as differences across gender in these outcomes. We find significant raw gaps in reading, science and mathematics scores between females in single-sex and mixed-sex schools and in mathematics scores for males across the same school types. However, after controlling for a rich set of individual, parental and school-level factors we find that, on average, there is no significant difference in performance for girls or boys who attend single-sex schools compared to their mixed-school peers in science, mathematics or reading. In terms of heterogeneous analysis, this finding is consistent across the performance distribution.