This report presents the results of a thorough study conducted by American Institutes for Research (AIR) to investigate the cost of providing an "adequate" education to California students attending public elementary, middle, and high schools. The study addresses the following question: "What is the cost of providing all California public school students with access to the California content standards and achieving appropriate levels of proficiency in accordance with standards established by the California Department of Education?" The AIR research team employed a professional judgment approach to costing out an adequate education. This approach leveraged the knowledge and experience of groups of expert educators, known as professional judgment panels (PJPs), to develop school programs that are capable of delivering an adequate education. For the purposes of this study, an adequate education was defined as providing access to instructional programs consistent with the California content standards and providing the opportunity to achieve the proficiency standards established by the California State Board of Education. The PJPs' school program designs needed to deliver adequate education at a minimum cost, and in a variety of contexts with different enrollment sizes and different student needs (i.e., different proportions of students eligible for free or reduced-price lunch, students classified as English learners [ELs], and students enrolled in special education). Chapters in the report include: (1) Introduction and Overview; (2) Measuring Adequacy Cost Estimates through the Professional Judgment Approach; (3) Translating Resource Specifications into Cost Estimates; (4) "Costing Out" California Adequacy: The Results; (5) Summary and Conclusion. [For the appendices to this report, see ED594741. For a related research summary, see "Working Toward K-12 Funding Adequacy: California's Current Policies and Funding Levels. Research Brief. Getting Down to Facts II" (ED594719).]