How we ranked the schools

The Sun-Times uses a well-known statistical method called standardizing to analyze the reading and math scores of every public school student in the state who took either the Illinois Standards Achievement Tests, given in grades three through eight, or the Prairie State Achievement Exam, given in grade 11.

The method compares each student's score with the state's average score and uses that information to create a school average that’s then compared to the average of other schools. Standardizing levels the playing field in years when one test, for whatever reason, might be harder to pass than other tests.

Only reading and math results were studied; they are the only tests that trigger sanctions under the federal No Child Left Behind law. Also, only tests from classrooms of at least 10 students were counted.

The Sun-Times’ top-elementary list reflects any school that tested at least two grades in the third- through fifth-grade range. The top middle-school list is based on any school that tested at least two grades from sixth through eighth.

Some schools, such as those serving grades K-8, might have been eligible for both the elementary and middle-school lists.

The rankings include percentiles, which are based on each school’s average reading and math score. The percentiles reflect the percent of students statewide who scored the same as or worse than the average student in the ranked school.

To select high-gaining elementary schools, the Sun-Times analyzed the 2003 and 2007 reading and math scores in third-, fifth and eighth-grade — the only grades to test those subjects in both 2003 and 2007. Again, the Sun-Times developed a standardized average score for each school that tested at least two of those grades, ranked them based on those scores, then looked for schools with large five-year changes in rank and other data.

The analyses were done by Sun-Times staff reporter Art Golab.

Rosalind Rossi