To assess the effect of inequalities in school resource inputs on student achievement, a model is proposed which uses hypothetical experiments to compare, on the one hand, the average achievement of student groups with their present school resources and, on the other hand, estimates of their average achievement after their school inputs are changed in specific hypothetical ways. Multiple regression analysis was performed with data gathered separately for Negro and white students in grades 6, 9, and 12, from which the Northern and Southern regions of the country. For each group under examination, the following clusters of school resources were changed to be the same as those held by students in another or by students of another race: (1) School facilities and programs, (2) school teaching staffs, and (3) characteristics of fellow students in the school. In general, changes in the composition of the student body were found to be the most important influence affecting student achievement, while school facilities ranked as the least important. The inequalities of total school resources were found to be greater between races within regions than between regions for a given race. (JH)