many states were reluctant to measure within-state, intra-district, horizontal equity because of the incompatibility of how expenditures, revenues, and pupils were counted. Researchers pushed ahead with data that were available and now the Department of Education produces data with standard definitions for all states (Common Core of Data from the National Center for Education Statistics). Likewise, the relationships between financing inputs and student performance have both driven and been driven by the kinds of data available. Twenty years ago, most researchers could access cross-section, district-level data, with very imperfectly measured inputs. Currently, the federal government sponsors several student-level surveys that follow students over several years (e.g., High School and Beyond and the National Education Longitudinal Study). In addition, many states collect and use student-level data for their performance systems. These student-level data allow researchers interested in production functions to refine their approaches. Remedies to court cases 25 years ago focused little on student performance, but as states have begun to produce numerous measures of performance by district (and often by school), these measures have been picked up by lawyers to help define and monitor adequacy of school finance systems. The importance of education to Americans, the large percentage of government expenditures devoted to it, and the constant attention of researchers, legislators, and lawyers have created pressures on state education departments and federal departments to provide better data. Whatever the direction of causality, it seems true that measures of school finance equity are intimately intertwined with the data that can be accessed by analysts.
If equity remains an important value, and adequacy continues to grow in its importance, then the research that links inputs to outputs will remain at the center of debates over school finance equity. Individual studies confirm that under some circumstances resources affect outcomes (Ferguson and Ladd, 1996; Mosteller et al., 1996; Krueger, 1997). If that research, combined with the extensive literature that already exists on the subject, can be interpreted to mean that when resources are used well they affect outcomes and when they are used poorly they do not, then we have a strong incentive to understand when effective use occurs.
Although it is reasonably safe to maintain that the financing of primary and secondary education in America will remain public, we can be less sure about the constancy of public provision in the traditional form of public schools organized in local school districts. Various changes that are being debated today, such as voucher schemes and charter schools, may lead to significant structural changes. How concepts of equity that developed within the framework of the traditional school district and public school will or will not fit with these newer arrangements remains to be seen.
In some ways, we have come full circle to the problems and issues that were addressed three decades ago. Whether we look across states, within states across districts, within districts across schools, or within schools across groups of students,