Over the past 10-15 years, there has emerged a growing consensus, supported by high-quality empirical research, that additional funding improves student outcomes (and funding cuts hurt those outcomes), particularly among disadvantaged students. There are, of course, serious and important debates about how education funding should be spent. Yet virtually all potentially effective policies and approaches require investment, often substantial investment. Proper funding, in other words, is a necessary (but not sufficient) requirement for improving student outcomes. Understanding, assessing, and reforming states' funding systems is therefore a crucial part of any efforts to bring about such improvement. This report evaluates the K-12 school finance systems of all 50 states and the District of Columbia. The latest year of data presented pertains to the 2019-20 school year, but it also examines trends in measures going back 10-15 years. The report focuses on three measures: (1) fiscal effort (how much states spend as a proportion of their economies); (2) statewide adequacy (whether aggregate spending is enough to achieve common outcome goals); and (3) equal opportunity (whether adequacy differs between higher- and lower-poverty districts). [This report was co-prepared by University of Miami School of Education and Human Development. For the fourth edition, see ED616520.]