This paper presents some initial ideas on how the theoretical concepts of the "insider" and the "outsider" might be re-examined in an era where advances in comparative, qualitative research methodologies seek to be more inclusive, collaborative, participatory, reflexive and nuanced. Earlier essentialist definitions of the outsider as detached and objective, and the insider as culturally embedded and subjective, are re-examined and set within an international research and teaching context that recognises the increased migration of people, ideas and educational policies. It is argued that, in the context of such change, it has become more difficult to categorise and label groups and individuals as being "inside" or "outside" systems, professional communities or research environments. Such essentialist notions, which often underpin the production of large-scale, international datasets of pupil achievement, need to be challenged so that more complex understandings can inform not only new methods of research design, research ethics, data collection and analysis, but also the creation of new knowledge, giving more validity to related education policy making. We recognise that individual and group identities can be multiple, flexible and changing such that the boundary between the inside and the outside is permeable, less stable and less easy to draw. The concept of a "third", liminal space may have the potential to encourage new meaning which is constructed on the boundary between worlds where historical, social, cultural, political, ethical and individual understandings meet.