Nine years ago the mayor of Chicago, Richard Daley, wrested control of the Second City’s schools from an entrenched bureaucracy at the city’s Board of Education and embarked on an overhaul of the city’s public school system.

He beefed up capital spending, instituted new training for principals, created schools for “student troublemakers,” mandated summer school for low achievers, and required minimum standards tests in the third, sixth, and eighth grades to make sure students could do the work before they were promoted.

If all this sounds familiar, it should. Mayor Bloomberg used the Chicago reforms as the starting point for his program to change New York city schools including, most recently, the expansion of a plan that requires students to pass reading and math skills tests in both the third and fifth grades.

The problem for Mr. Bloomberg is that the evidence is scant that draconian measures like holding children back are good for them.

Chicago, which has waged war on “social promotion” for seven years, has had a decidedly mixed experience. Just five months ago, Mr. Daley agreed to abandon a math skills test for struggling students and to focus exclusively on literacy.

“We’re still changing things to see what works,” said the chief executive officer of the Chicago Public Schools, Arne Duncan. “We test students in the third through eighth grades but we only hold them back in grades three, six, and eight. The system is a work in progress.”

To hear New York City education officials tell it, Chicago’s reforms were an opening gambit for New York’s reforms, but they have improved on the Midwest program.

“New York looks at a student’s class work, and works with teachers to assess students beyond their test scores,” Deputy Mayor Dennis Walcott said in an interview.

In the past year, Chicago has done something similar: it reviews a student’s summer school work in addition to test scores.

Retention of students, making them repeat a grade, is the most controversial aspect of the school reforms.

The number of Chicago students held back since Mr. Daley won control of the school system in 1995 has quadrupled.

While on the surface that might indicate success because students who can’t do the work are identified, a team of researchers at the University of Chicago’s Consortium on Chicago School Research found otherwise.

In a report on Chicago’s social promotion policy, they found that about half the students who spent an extra year in the same grade and attended summer school improved their scores on standardized tests, but the remaining students held back continued to struggle.

Some 20% of the children held back in the first and second grades were held back again in the third grade. And some students attended the same grade three times.

The New York Department of Education’s senior instructional manager for assessment and accountability, Lori Mei, said the New York program would start with individualized programs to avoid that problem.

“The major difference is that the kids in Chicago that are getting retained are getting the same thing the second time around,” she told the Sun. “Our program is a whole other thing. We are doing a very tailored approach.”

And the city is spending money to ensure their approach works. Mr. Bloomberg has allocated $20 million to fund tutors, computer-based learning, and special after-school, weekend, and holiday help sessions for struggling students.

Mr. Bloomberg’s plan, which still needs approval from the Education Policy Board, would create “Saturday Academies,” which would meet for five hours on 24 Saturdays throughout the school year.

The Saturday Academy students will be identified using in-class assessments and test scores from previous years and will receive early, consistent supplementary instruction during the school year. Chicago hasn’t done that.

Nearly a third of Chicago students who repeat a grade, or attend an alternative school, drop out when they reach the age of 16, according to the University of Chicago report.

Many of those children haven’t completed the eighth grade. Although the total number of dropouts in Chicago has declined, Chicago school officials concede that there has been an increase in the number of students dropping out in earlier grades.

A decade ago, Chicago’s dropout rate was as high as 25%, Mr. Duncan said. Now the rate is about 13%. The New York City dropout figure in 2002-03 was 10.3%.