This paper uses part of the data from a larger qualitative inquiry in two International Baccalaureate schools, one in Australia and one in an Indian Ocean Island Nation (a pseudonym), to identify the factors and forces that contribute to the sense of self and understanding of and engagement with the notion of international mindedness in two 'third culture kids'. Socio-cultural theory is used as a conceptual framework to explore cross-cultural differences and similarities between the students and the schooling contexts. Analysing the students' perspectives about their understandings of international mindedness through grounded theory methods, the paper also develops hypotheses on the notions of being, belonging and becoming.