Chicago's African-American and Latino students start elementary school behind their black and Latino counterparts statewide but ultimately catch up and outscore them in reading by eighth grade, new University of Chicago research says.

The scores of Chicago Public School students in general lag behind non-CPS kids in all grades in reading and math, but that gap narrows considerably between third and the upper grades, the U. of C. analysis of 2006 state tests found.

"This finding suggests that longer enrollment in CPS leads to better relative performance, not worse as was suggested previously," wrote lead author John Easton, director of the U. of C.'s Consortium on Chicago School Research.

If CPS' racial composition matched the state's, CPS would either outscore or match the rest of the state, Easton said. Chicago is nearly 90 percent black and Latino.

"Chicago is usually looked at as being lower performing than the rest of the state, but when you get to this level, it's not the case," Easton said. "Really, the state should be learning from Chicago, not the other way around."

Black and Latino students still significantly underperform whites, and CPS as a whole still trails the rest of the state, but this shows progress, said one outside researcher.

"This doesn't mean CPS kids will eclipse suburban kids because they're starting at such a low point, but it's encouraging," said Herbert Walberg, emeritus professor of education and psychology at the University of Illinois.

Easton separated the state into two groups -- CPS vs. all other districts -- and compared performance, in general and among racial groups. No one else has looked at data this way for at least a decade.

He found that black third-graders in Chicago trailed black third-graders outside CPS by seven points on the reading portion of the 2006 Illinois Standards Achievement Test. By eighth grade that had reversed, with a point advantage for Chicago kids.

Latino third-graders trailed non-CPS Latinos by three points. By eighth, Chicago kids were ahead by four points. Among whites, Chicago third-graders started off ahead and gained more ground by eighth. The same pattern applies to math for all racial groups, but it's not as strong, Easton said.

This trend played out at Columbia Explorers Academy in Brighton Park, where 96 percent of students are Latino.

"My population comes from the rural parts of Mexico," said Principal Jose Barrera. "Nothing happens overnight. . . . It starts coming into form and then it's there by eighth."

Easton analyzed a set of controversial test results. Scores on the 2006 ISAT skyrocketed over 2005, particularly in Chicago. Some questioned whether changes to the test and its administration played a role, including an extra 10 minutes for students per section and an easier eighth grade math score.

Easton tried to sidestep that controversy by making no comparisons to previous years. But Don Moore of Designs for Change said an easier test in 2006 may have helped Chicago more than other districts. That's because schools that start far behind can pick up more ground on an easier test than higher-scoring schools, he said. Easton disagreed, saying the growth in Chicago scores wasn't confined to the weakest kids.

Chicago kids also may have performed better on 2006 tests because, for the first time, they took two diagnostic reading tests before the ISAT. The same company wrote the ISAT and the diagnostic tests.

Schools CEO Arne Duncan called the results "exhilarating," but said it forces CPS to ask hard questions: "Why are so many students coming in so far behind? We have to challenge ourselves, the larger society and parents on what we're doing before kindergarten so they come to school ready to learn."