Teachers in the early years of primary school play an important role in supporting students' oral language skills; however, there is evidence to suggest many Australian teachers are not adequately prepared to provide systematic, evidence-based instruction in oral language and early literacy. The aim of this study was to describe the observed and self-perceived changes in knowledge, practice and beliefs of teachers who participated in a sustained oral language professional learning program. A second aim was to determine whether this development was adequately accounted for by current models of professionalism and professional development. Three case studies are presented, using data taken from a survey of teacher knowledge and the analysis of samples of classroom talk at three time points, and semi-structured interviews. These case studies illustrate that despite participating in the same sustained professional learning program, there was inconsistency in the teachers' outcomes. Growth in knowledge was variable; and change in self-rated ability to provide instruction was influenced by observed student outcomes (which teachers attributed to change in their practice). In one case, professional growth was restricted by factors within the school environment.