This study features a design experiment of a teacher study group model of professional development. Our goal was to support teachers' development of the knowledge and practices that promote children's emergent literacy in the preschool classroom. Three sequential cohorts involving a total of 19 teachers in a district serving a high-need, under-resourced community participated in a year-long intervention; child outcomes were examined for 101 randomly selected preschool children. Consistent with previous research, teachers demonstrated low initial levels of knowledge of phonological awareness, and phonological awareness activities in classrooms were of low quantity and quality. Pre- and post-test analyses revealed significant changes in teachers' phonological awareness ability, content knowledge, and pedagogical knowledge. Increases were also seen in the quantity and quality of phonological awareness activities in the classroom. Finally, the children in our sample demonstrated significant gains on a measure of their phonological awareness skills and made more progress in this area over the course of the study than would be expected based on national norms of same-aged children. This work offers initial support for the use of relationship-based models of professional development as a means to address many of the challenges inherent in the current early childhood education landscape. Teacher study groups offer a promising means of developing a qualified, competent, confident workforce that is well equipped to meet the needs of the children they serve. (author abstract)