Student teachers are concerned with discipline as in-service teachers do. The study aims to explore their knowledge of classroom discipline. The study is qualitative, descriptive and narrative in nature. The research method of unstructured interviews was employed to capture their professional knowledge of classroom discipline. Ten student teachers from Hong Kong were involved. Throughout the two-month period of their teaching practicum in Hong Kong secondary schools, three interviews for each participant were conducted. The study illuminates the classroom experience of student teachers and reveals that they found difficult to transfer concepts and skills mastered during their training to the classroom. Further, with the exploration of the convictions and meanings that have arisen from their experience, the initial findings enhance our understanding of their needs regarding classroom discipline. The implications to the professional development, future studies into discipline, and the promotion of positive classroom discipline strategies will be given.