The MacArthur/Spencer special project on Illinois school finance is dedicated to the exploration of three central concepts in Illinois school finance: equity, adequacy, and efficiency. While most reports on the project have dealt directly with equity and adequacy, this report confronts the issue of efficiency by discussing the policy and legal implications (within the constraints established by "Rose versus the Council for Better Education") of identifying school districts as being technically economically efficient. The report discusses the limitations of the regression analysis developed to determine the efficiency of the project. The conclusion that professional effectiveness and economic efficiency interrelate suggests the need for further tests of validity and reliability on the instruments used to measure such efficiency. (JAM)