Educational Evaluation and Policy Analysis Suimmer 2003, Vol. 25, No. 2, pp. 119-142 Resources, Instruction, and Research David K. Cohen Stephen W. Raudenbush Deborah Loewenberg Ball University of Michigan Many researchers who study the relations benveen school resources and student achievement have workedfrom a cautsal model, wvhich typically is implicit. In this model, some resouirce orset of resources is the causal variable and student achievement is the ozutcome. In afewv recent, more nu(anced versions, resource effects depend on intervening influences on their use. We argue for a model in wvhich the key cautsal agents are situated in instruction; achievement is their outtcome. Conventional resourcescan enable or constrain the causal agents in instnrction, thus moderating their impact on student achieve- ment. Becautse these causal agentsinteract in wvays thzat are unlikely to be sorted out by multivatiate analysis of natutralistic data, experimental trials of distinctive instnrctional systems are more likely to offer solid evidence on instnrctional effects. Keywords: expetiments, instnrctional effects, research and policy, school effects For most of the history of U.S. public schools, conventional educational resources were seen as the key to making schools work. Educators, parents, and policymakers acted as though they assumed that money, curriculum materials, facil- ities, and their regulation, caused learning. Many still seem to assume that, as they write about the "effects" of class size or expenditures on learn- ing. The phrasing implies that resources carry "capacity." Regulation has been thought to work by steering resources and thus capacity, within and among educational organizations; the idea is that ability grouping or segregation influence achievement by influencing access to resources. These assumptions made school improvement seem straightforward: allocate more resources or regulate schools' allocation of them. Access to schooling does affect outcomes. Stu- dents learn algebra in classrooms, not on the street. High school students who study in academically more demanding curricula learn more than stu- dents in less demanding curricula, even when stu- dents' earlier achievement is taken into account. Disadvantaged students' achievement 'May fall off when they do not attend school in the summer (Alexander, Entwisle, & Olson, 2001). But sev- eral decades of research suggest that access itself does not cause learning. Researchers report that schools and teachers with the same resources do different things, with different results for learning. Earlier versions of this study were published in Boruch, R. & Mosteller, F. (Eds.), Evidence Matters: Randomized Trials in Edu- cation Research. Brookings Institution, 2002 and in the Center for Teaching Policy's working paper series (http://depts. washington.edu). Seattle: University of Washington. We thank Simona Goldin for extraordinary research assistance, and Jere Brophy, Anthony Bryk, Jeremy Finn, Fred Goffree, Henry Levin, Richard Mumane, Will Oonk, Annemarie Palincsar, Jeremy Roschelle, and Alan Ruby for helpful comments. Grants from The Pew Charitable Trusts and the Carnegie Corporation of New York to Michigan State University and The University of Michigan, from The Office of Educational Research and Improvement (U.S. Department of Education) to The Consortium For Policy Research in Education (CPRE) and The Center For the Study of Teach- ing and Policy, and The Atlantic Philanthropies, to CPRE, supported various elements of the research. None of these people or agencies are responsible for the ideas in this article. 119