This dissertation is a single case study of a teacher, Wanda, transitioning from teaching Kindergarten to teaching pre-K. A veteran public school Kindergarten teacher with more than ten years experience, Wanda saw teaching pre-K as an opportunity for professional growth and development. Wanda's transition to teaching pre-K was also a transition for her school district, which was inaugurating public pre-K for the first time. To support new to pre-K teachers, our research project--the 4K-PD project--partnered with the school district and undertook to design a series of four professional development courses in concert with the school district. As a member of this team, I was assigned to observe and work with Wanda in her classroom throughout the pre-K year. While moving from Kindergarten to pre-K did not immediately present as a practice and identity changing experience, the transition was unsettling for Wanda. What Wanda did not expect were the vast differences in both practice and conceptions of curriculum that entering the domain of pre-K heralded. In Kindergarten, Wanda had been required to implement a standards-based, pre-determined curriculum. In pre-K, however, Wanda was encouraged and expected to create an emergent, play-based curriculum that reflected the needs and interests of her students. Viewing this opportunity as both exhilarating and terrifying, Wanda used our time together in her classroom, her growing knowledge of early childhood conceptions of curriculum from the 4K-PD course, and her rich existing knowledge base to develop an emerging pre-K teacher identity and curricular experiences for her students. This process was not easy and required hard choices and considerations about what constituted best practices in early childhood. By the end of her first year of teaching pre-K, both Wanda and I had learned a great deal about what it meant to be a teacher, a learner, and to make sense of practice in the pre-K borderland that exists between the worlds of Early Childhood and Elementary education. This dissertation explores these lessons and makes recommendations for teacher educators as they work to support new to pre-K teachers. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]