Race and class are two of the most significant factors associated with educational inequality within and across societies. However, their definitions and significance vary over time, and from one place to another. As subjective factors related to identity, they also impact on one another in their effects on educational access and equity. These issues create challenges for conducting comparative educational research that effectively explores one or both of these factors. This essay examines challenges employing race and class in comparative educational research. Race and class are analysed separately, illustrating that ethical and political issues, not just conceptual miscommunications, are at stake in defining and using these categories. The geographical and political complexity of using race and class are also reflected on more generally, and the argument is put forward that analytic and self-reflexive understanding of diversity is needed for the development of fruitful understanding of the relationship between race and class and educational equity and justice.