This paper uses mixed methods to explore perceptions of international-mindedness within two case study schools in Istanbul, Turkey: a national school with mostly Turkish students and an international school with students from many nationalities. Using a conceptual framework developed by an international education programme, the authors critically analyse pillars of international-mindedness: multilingualism, intercultural understanding, and global engagement. Findings reveal that the national school was striving to overcome limitations of homogeneity, while the international school struggled to address its assumptions that a heterogeneous population alone would be enough to encourage intercultural understanding. Neither school had developed clear conceptual links among multilingualism, intercultural understanding, and global engagement. Thus, deliberate efforts are needed to provide students with experiences that foster international-mindedness. Other researchers and educators can use this framework and associated methods to examine how international-mindedness is implemented in different schools in other regions of the world.