State-level policy attention to young children's early learning opportunities burgeons; a sense of urgency exists to identify reform agendas that are both effective and sustainable. "P-3" often is used as the term for the first level of a seamless P-20 system that stretches from early childhood through post-secondary education. While it is commonly agreed that P-3 spans the early childhood and early elementary education years, there is a lack of clarity about how to understand and implement P-3 at the state policy level. This research begins to build greater agreement and understanding of how to position and structure P-3 as a credible and meaningful state-level policy reform agenda. Constructivist grounded theory framed the inquiry that relied on multiple data sources and mixed methods analysis. Central to the methodology, the Delphi Method was used to engage prominent state-level policy leaders in a dialectic process to identify the most compelling and important components of P-3 as a state-level policy agenda. Four primary dimensions of P-3 were addressed. First, it was determined that the ideal P-3 age range begins with attention to "pre-natal" development and extends through "grade 3." Second, the most compelling rationale for state policymakers to pursue P-3 reform is the need to close early achievement gaps. Third, the most important principles to guide P-3 reform include addressing the whole child, emphasizing that school readiness has multiple dimensions, and ensuring continuity and coherence of children's experiences. Fourth, while there exists a range of policy types that might be included in a state-level P-3 reform agenda, the viability and feasibility of doing so varies across several dimensions related to technical feasibility, value acceptability, and anticipation of future constraints. The study holds significance for future exploration and analysis in both research and state policy. Fundamentally, the study reveals that state policy leaders view P-3 as a credible and potentially meaningful reform agenda. The study also highlights the need to expand both conceptual and empirical understanding of how to reform pre-natal, early care and education (ECE), and K-3 systems to establish and strengthen coherence across the full pre-natal through third grade age continuum. [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.]