International kindergartens, which offer an immersive dual-language (English and Chinese) environment, are popular among middle-class families in Hong Kong. The international learning and teaching environment is cultivated primarily by developing a diverse workforce, in which Chinese-speaking (Putonghua and/or Cantonese) teachers with local training or from mainland China generally work with their English-speaking counterparts from overseas in the same classroom. Such heterogeneity has complicated the already challenging concept of collaborative teaching. This article presents a case study of the collaborative teaching practice in a trilingual international kindergarten which had been established for over 50 years. Through in-depth interviews, questionnaires, text messaging, document analysis, site visits, and observations, the study examined the collaborative teaching practices among international colleagues in the kindergarten. The findings revealed that collaboration among international colleagues was made successful by: (1) senior management and teachers sharing a common goal; (2) a dynamic whole-school supportive structure that embraced heterogeneity; and (3) the development of a shared culture of professional learning. The implications of these findings for management, practice, and research are discussed, including the need to foster a culture of collaboration, the importance of professional development, and the need for further research on collaborative teaching practices in diverse educational settings. Copyright © 2023 Springer.