For much of his tenure as mayor, Michael Bloomberg put public school student test scores at the top of his résumé. Not anymore.

The city's scores plummeted last year after state officials admitted that the exams had become too easy and recalibrated their scoring. This year's exams were longer and more difficult, prompting warnings of a repeat scenario when the results are released Monday.

“I think you are going to be looking at a similar or potentially even worse situation,” said Eva Moskowitz, chief executive of school operator Success Charter Network and a supporter of many of Mr. Bloomberg's reforms.

The scores will provide yet another data point in the controversial and oft-disputed education legacy of Mr. Bloomberg, whose overhaul of the once-moribund city schools began when the Legislature granted him control of the system in 2002.

Department of Education spending has since nearly doubled to about $24 billion, yet optimism for the mayor's reforms has turned to wariness and, in many circles, opposition. While the high school graduation rate has improved by 18 percentage points, to 65%, the graduates are often unprepared for college: Nearly three-quarters of those who enroll in city community colleges require remedial classes. And grumbling over the mayor's emphasis on standardized testing was legitimized by last year's drop in scores, which undermined the public's faith in the previous results.

In the span of a year, the lower scores, along with the resignations of two schools chancellors and threats of teacher layoffs, have pushed public opinion of the mayor's handling of education to a new low. Two weeks ago, a Quinnipiac poll showed that 58% of voters disapproved, compared with 24% in 2002. When Quinnipiac put the question to public school parents, a startling 69% said they disapproved.

Public confidence shaken

The troubles began in earnest in July 2010, when state test scores showed that the vast improvements touted by the mayor during his 2009 re-election campaign were overstated. Instead of two-thirds of city students being deemed proficient in English and 82% in math, more than half failed English, and only 54% passed math. The results shook public confidence in the data that the mayor had long trumpeted to validate his sweeping changes. Parents and teachers felt the mayor had misused numbers that education experts knew to be suspect.

“The Department of Education and the mayor have been quick to declare victory and reluctant to speak honestly about the challenges in the system,” said Pedro Noguera, an education professor at New York University. “This has made it difficult to have an honest discussion about where the challenges remain and what we need to do to confront those challenges.”

The city's scores on a nationally administered fourth-grade reading and math test have increased substantially, compared with other urban districts, but eighth-graders have shown no progress in reading since 2002.

The November departure of Joel Klein—a polarizing chancellor who was alternately praised and pilloried for closing 89 “failed” schools and opening 126 charter schools—led to the first major crisis of Mr. Bloomberg's rocky third term. By appointing former Hearst magazine executive Cathleen Black as chancellor, the mayor appeared out of touch. Education reformers feared Mr. Bloomberg had lost his zeal for change; parents simply felt insulted, a grievance Ms. Black aggravated when she mocked parents at a hearing and joked about birth control as the solution to school crowding.

Ms. Black was replaced after four months by Deputy Mayor Dennis Walcott, a product of Queens public schools and a conciliatory figure. His appointment restored morale within the DOE, which had lost several top deputies. But parents still feel left out.

“The tension between the mayor and parents and the community has detracted from education reform,” said Kim Sweet, executive director of the nonprofit Advocates for Children of New York. “The mayor is losing input that is very valuable. He's losing partnerships and ideas.”

The “education mayor” has taken his lumps yet pressed ahead, sometimes aided—but more often denied—by the state Legislature. His threat to lay off teachers antagonized their union as well as parents concerned over rising class size. The gambit also failed to persuade legislators to end “last in, first out” rules that protect senior teachers from layoffs regardless of their performance. Layoffs were averted thanks to unprecedented funding from the city, but the mayor got little credit.

Mr. Bloomberg has rarely skimped on education spending. He has increased teacher pay 43%, allowing principals to compete with suburban districts for talent. Until now, however, New Yorkers had little idea what they were getting for the extra $2.5 billion in salaries, $1.4 billion in fringe benefits and $3 billion in pension contributions they paid last year. Perfunctory teacher evaluations rated 98% of classroom educators satisfactory. Only last month did a more rigorous evaluation required by the federal government find 18% of teachers to be ineffective. The mayor has long fought for more power to fire poor teachers.

Unfair perception?

The city also doled out $56 million in privately raised funds for a pay-for-performance program, but abandoned it last month after concluding that it improved neither student performance nor teacher satisfaction. Critics saw it as an example of the administration throwing money at unproven strategies.

As Mr. Bloomberg approaches the final two years of his administration, his education legacy is more positive than parents give him credit for, but it is a complex mix, education experts said. Part of the reason is perception.

“We don't remember the days when the system was paralyzed politically,” said Joseph Viteritti, professor of public policy at Hunter College and a city schools official from 1978 to 1981.

But, he added, “the level of college preparedness is terrible.”

To improve it, the DOE is rolling out a curriculum that emphasizes children's ability to analyze ideas, express their thoughts and use math to solve everyday problems, rather than fill out ovals for multiple-choice tests.

For the mayor to ensure his education legacy, observers said, college readiness must improve. Teachers and schools will be judged by their ability to prepare non-native speakers, children from poor areas and those with developmental delays for college and the workforce.

Sol Stern, a senior fellow at the Manhattan Institute, a conservative think tank, said improved reading scores on the national tests will be “the surest sign as to whether more New York City kids become college-ready by 12th grade.”

One promise of mayoral control was better coordination between agencies. Poverty is an especially strong indicator of student performance, but critics said the mayor has not done enough to coordinate his agencies to alleviate the barriers that poor children—mostly black and Latino—face. A $127.5 million program announced by the mayor last week will address the problem.

Mr. Bloomberg's most significant change has been to transform “a bureaucracy that wasn't managing to deliver in any way, shape or form,” said Merryl Tisch, chancellor of the state Board of Regents. Another key priority has been to improve the teacher workforce, observers said.

But definitive results that cement Mr. Bloomberg's legacy as the education mayor may not come before he leaves office at the end of 2013.

“These reforms were always long-term,” said James Merriman, chief executive of the New York City Charter School Center. “This is revolution by evolution.”