Despite increasing student diversity in recent decades amongst Irish school populations, similar to the international context, the teaching population in Ireland has remained rather homogenous, with the majority being from the dominant ethnic, dis/ability, and social class groups. In the context of a national policy commitment to diversify our teaching force and to widening access to the professions, we need solid data regarding the diversity profiles of those entering the teaching profession. The Diversity Profiling Initial Teacher Education (DITE) in Ireland research project, funded by the Irish Research Council, is a mixed-methods, cross-sectional longitudinal study. It seeks to gather and analyse background and attitudinal data from applicants and entrants to initial teacher education (ITE) programmes in Ireland, via online questionnaire, to explore and compare their diversity profiles, experiences and motivations. To compare the diversity profiles of applicants to entrants, we need to track all applicants in terms of the subsequent outcome of their application. For ethical reasons, this needs to be done in an anonymous fashion, which presents a significant methodological challenge. Further, a national study of this kind requires the formal collaboration of the various ITE providers and application management systems. In this paper, we examine the various methodological challenges encountered and the sorts of solutions we have implemented.