How we ranked the schools

The Chicago Sun-Times' annual rankings are based on average scores on 2006 state reading and math tests, not the percent passing or gains.

The Sun-Times used a statistical method called standardizing to analyze the Illinois Standards Achievement Test scores of every public school student in the state. The method compares each student's score with the state's average score, and each school's average with that of other schools.

The results should be unaffected by a state decision to lower the passing bar, from the 67th to the 38th national percentile, in eighth-grade math.

Because ISATs were expanded for the first time to all grades, third through eighth, the Sun-Times created two lists -- one for top elementary schools, based on third- through fifth-grade scores, and the other for middle-grade programs, based on sixth- through eighth-grade scores.

Schools serving kindergarten through eighth graders were eligible for both lists.

As in years past, only public schools with at least two grades tested and at least 10 students in each grade were analyzed.

Only reading and math results were studied; they are the only tests that trigger sanctions under the federal No Child Left Behind law.

High school results on Prairie State Achievement Exams are due March 13.

The analysis was done by database reporter Art Golab.

--Rosalind Rossi