This study focuses on a cost analysis conducted for the purpose of improving education in Illinois. The study explores educational funding in Illinois using 2005 Illinois School Report Card data, as collected by the Illinois State Board of Education. The study strives to make transparent the purpose, key stakeholders, methods, and intended use of the information developed as a means of ensuring appropriate application of results and to respond to questions of reliability and validity. The purpose of this study is to illuminate information that might generate educational change to improve education for all youths in Illinois. The researchers attempted to respond to local information needs and state education concerns in the context of the study's purpose: improving education. The following evaluation questions were used to guide study development and analysis. What is the nature of the relationship between measures of educational achievement and funding? What is the nature of the relationships between school composition, achievement, and funding? What is the nature of the relationships between school environment, composition, achievement, and funding? The study is intended to respond to the differing information needs of each of these constituencies and therefore uses both descriptive and inferential statistical analysis as tools in examining the 2005 Illinois School Report Card data. The findings developed from analysis herein are intended to represent a set of evidence that is bounded in interpretation by the unique context of Illinois school funding, the limitations of the data analyzed, and the methods used to analyze the data. The following are appended: (1) Top-Performing Elementary School District Analysis; (2) Top-Performing High School District Analysis; and (3) Top-Performing Unit District Analysis. (Contains 6 tables.)