Purpose: Research shows data-informed leadership matters for school improvement and student achievement, but less is known about what motivates leaders' data use toward such outcomes, particularly in the Catholic school context. Design/methodology/approach: This qualitative interview study uses interview (n = 23) data from a sample of Catholic school leaders to unpack how they conceptualize data, the motivations encouraging their data use and the challenges inhibiting data routines. Findings: Catholic school leaders largely shared a narrow definition of data as quantitative, standardized achievement data, were motivated by a moral imperative to meet students' needs and faced several common challenges, including time constraints, uncertainty in measurement, limited capacity and resources and issues of turnover at the classroom and school levels. Practical implications: School leaders can assuage tension around data by broadening the scope of measures and appealing to teachers' sense of personal responsibility and commitment to students. Originality/value: These findings extend the research in three ways. They bring to light an important tension between data-informed practice and a whole child approach to education, highlight the possibility of motivating data use through conscience rather than compliance and provide insight into data perceptions in private schools, an understudied context in the literature.