A boundary is a metaphor for an experience of discontinuity wherein a socio-cultural difference is perceived as a challenge or obstacle in action or interaction. This case study explores eight student teachers' perceptions of boundaries during an international teaching internship to identify where experiences of professional learning originate. We found four types of boundary experiences related to discontinuity: (1) existing pedagogical approaches, (2) personal aspects, (3) a specific school type or culture, and (4) the world outside the classroom. Results suggest that the learning potential of experiencing discontinuity resides in situations wherein student teachers' beliefs are being questioned, thus making the student teacher aware of their implicit beliefs. Student teachers' attempts to reposition themselves while experiencing discontinuity resulted in questioning their existing ways of thinking and acting. Everyday teaching approaches were no longer always taken for granted, thus opening alternate perspectives. In this study, student teacher experiences of discontinuity had various dimensions (cultural, professional, and personal), which also determined their learning potential.