This study investigates how characteristics of a collaborative professional learning activity support and hinder teacher learning and growth by examining the experiences of three Korean secondary teachers who participated in a school-initiated collaborative teacher learning project. The findings demonstrated that this learning opportunity supported teachers in their learning and professional development in the following ways. First, teachers experienced professional growth through collaborative learning with colleagues. Second, teachers learned to self-reflect on their classes. Third, the program fostered an inquiry stance toward teaching. Also identified are some of the obstacles encountered, such as time constraints, psychological barriers, and the lack of a discussion culture.