How we ranked the schools
For a more than a decade, the Chicago Sun-Times has based its exclusive rankings of schools on average scores on state achievement tests, not on the percentage who meet state standards — a measure that has come under criticism.
Only 2012 reading and math results from the Illinois Standards Achievement Tests and the Prairie State Achievement Exams taken last March and April were analyzed. Results in those subjects can trigger sanctions under the federal No Child Left Behind law.
Elementary school rankings are based on schools that tested at least two grades, third to fifth.
Middle-school rankings reflect at least two tested grades, sixth through eighth. High school rankings are based on 11th-grade results. A K-8 school could be ranked among both elementary and middle schools.
The rankings use a statistical method called standardizing to analyze the “scale score” of every reading and math test statewide.
The method compares each test score with the state average and creates a school average that’s compared with other schools’ averages. Standardizing levels the playing field in years when one test might be harder to pass than others.
The rankings include percentiles, reflecting the percentage of Illinois students who scored the same as or worse than the average student at each ranked school.
Sun-Times staff reporter Art Golab performed the analyses.