Being aware of various practical problems when using a collaborative approach as a "metastrategy" in school-based professional development, educators have been concerned about a mismatch between the traditional teacher culture, which is normally associated with individualism, and a new form of collaboration, which entails change and openness. This exploratory research, using a questionnaire survey and interviews, attempts to identify factors affecting professional development through peer collaboration, particularly for Korean teachers of English in secondary schools, and to suggest recommendations for improving English language teacher development in Korea. Such recommendations include an emphasis on practical teaching methodology, the perception of professional development as sharing experiences, positive past experiences, a cooperative school culture, and a working environment conducive to working together.