This paper presents a comprehensive framework for evaluating and reforming education finance systems to ensure equity, adequacy, and equal opportunity in publicly funded education. We summarize decades conceptual work, explaining our evolving understanding of the role and purpose of school finance systems, leading to our current framing that the purpose of these systems is to deliver the resources necessary for schools to provide all children equal opportunity to achieve common, adequate outcome goals. We provide a two-part, four step sequence of empirical methods for 1) evaluating whether and to what extent current systems achieve this goal (Part 1: What is), and 2) (Part 2: What should be) calibrating or recalibrating a school funding system to better achieve this goal. We follow with a discussion of lessons learned from recent applications of our framework in U.S. states, in both elementary and secondary school systems and community college systems. We conclude with implications for the path forward for broader application of the framework.