This chapter presents a study on teacher learning based on a case of four initially out-of-field teachers in Indonesia as they develop to become master or accomplished teachers. Employing the conceptual framework of “boundary crossing” and the notion of “boundary objects” (), the study investigates how teacher learning occurs where boundaries serve as not only sources of potential difficulties, but also opportunities for innovation and renewal related to perception of professional identity and practice. A component of the learning includes a move from “non-teaching space” into “teaching space”. In-depth interviews with teachers and the analysis identifies four dialogical learning mechanisms: identification, coordination, reflection, and transformation. Findings show that as teachers cross boundaries, they identify discontinuities between different teaching spaces, while finding sufficient boundary objects which establish recognizable actions and interactions in the out-of-field space. The discussion includes the role of teacher reflection within a professional learning community to build on their experiences and ease boundary crossing. This study informs both the educational realities faced by many Indonesian youths in under-resourced communities where teachers commonly teach out-of-field; as well as of youths who are in teacher education programs to prepare themselves to be adaptable, capable, and informed.