The early childhood years are a unique and distinctive time where teachers can provide children with opportunities to cultivate not only academic skills, but also foster their social emotional competencies (SEC) to prepare them for their future endeavors. For children to be successful in an early childhood education (ECE) program, teachers must be equipped with the appropriate knowledge and skills to foster students' academic and social emotional development. One method of improving teacher effectiveness is through the use of professional development (PD) opportunities. Providing teachers with effective and meaningful PD opportunities is especially important when introducing novel instructional approaches, such as STEAM (science, technology, engineering, arts, and mathematics). STEAM instruction focuses on solving real world problems that are relevant to students' interests and lives through the transdisciplinary integration of various content areas using strategies such as inquiry-based instruction, problem solving, and collaboration. Because teachers are the main implementers of any new teaching approach, the success and/or failure of that approach hinges on their beliefs of effectiveness. The purpose of this three-paper dissertation was to investigate how ECE teachers conceptualize STEAM instruction and how providing effective PD opportunities for teachers can inform their classroom practices to support children's development of SEC. First, in Chapter Two, I examined teachers' experiences with and perspectives on an innovated approach to a STEAM PD workshop. Second, in Chapter Three, I developed and introduced a novel framework for conceptualizing ECE STEAM instruction with the integration of children's SEC. In Chapter Four, I investigated the ways in which ECE teachers from STEAM-focused schools conceptualize: (1) the practice of STEAM instruction; (2) their experiences with STEAM instruction in the classroom; and (3) the relation of STEAM instruction to children's development of SEC. Findings from this dissertation aid in expounding the assorted ways in which ECE teacher PD, STEAM instruction, and children's SEC are connected. Collectively, the findings offer teachers, administrators, and PD creators a deeper understanding surrounding the effective and successful implementation of STEAM instruction in ECE to afford children with opportunities to develop their SEC. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]