This study presents a new approach to identifying economically efficient school districts in Illinois and provides a preliminary analysis of the determinants of public schools' economic efficiency. Economically efficient schools are those attaining higher than expected test scores at lower than expected costs. Expectation is based on school district socioeconomic status and property wealth. Using the quadriform procedure, which combines two related data sets to produce a visual representation, 75 K-12 Illinois districts were identified as economically efficient. The study differentiates between the concepts and goals of economic efficiency and professional effectiveness. Numerous internal budget ratios in school districts failed to discriminate between economically efficient and inefficient districts. Generally, characteristics beyond local superintendent and board control contributed more to determining economic efficiency than factors under administrative control. Some partially controllable factors do seem to affect economic efficiency, such as district size and pupil transportation investment. Other administratively controlled variables are listed. Since so many factors are outside administrative control, districts' economic-efficiency status may simply be fortuitous. Included are six pages of suggested readings and six appendices containing survey data. (MLH)