Montgomery County’s efforts to close the gap in achievement between its high-poverty and low-poverty high schools have not worked, with widening disparities on many measures of student success, according to a county report released Tuesday.

The 59-page study found that the schools are increasingly divided by income, race and ethnicity, with African American, Latino and low-income students more isolated than they were three years ago.

Montgomery’s school system has “lost ground in achieving its racial and economic integration goals,” according to the report from the County Council’s Office of Legislative Oversight.

The report, which comes amid county discussions about the school district’s $2.3 billion budget request, creates a portrait that is at odds with the popular image of Montgomery as a prosperous suburb of high-performing schools. It points to an economically divided county where the level of high school poverty appears to make an academic difference.

Superintendent Joshua P. Starr acknowledged that the school system has “a longstanding and persistent achievement gap,” writing in a response that was included in the report that “eliminating the achievement gap is at the core of our strategic priorities.” He wrote that his proposed budget for 2015 calls for additional funds to encourage strong teachers to move to or stay in high-needs schools, add counselors and psychologists, focus support for English learners, reduce class size and strengthen alternative programs.

But amid the district’s efforts, the share of black and Latino students grew in high-poverty schools, while the share of white and Asian students grew at low-poverty schools during the past three years, according to the report. Performance also diverged.

At high-poverty schools, students were 9 percent less likely to graduate on time and 45 percent less likely to earn at least one passing score on an Advanced Placement exam than their counterparts at wealthier schools. Students at high-poverty schools were 29 percent less likely to complete an Algebra 2 course with a C or better by the 11th grade, and they were 56 percent less likely to score a 1650 or better on the SAT than students at more affluent schools.

Students at high-poverty schools also were more likely to be suspended from school or drop out of high school, the report says.

“An achievement gap exists by high school type,” the report says.

By contrast, economically disadvantaged students did better on a number of measures at campuses with a larger share of middle-class or affluent families, which included high schools in Bethesda, Rockville, Poolesville, Potomac, Damascus and Clarksburg.

While the district overall is seeing more students in poverty, the report cites a “flight of middle-class students” from the district’s higher-poverty schools, many in or near Silver Spring, Wheaton and Gaithersburg.

The study was a follow-up to one examining performance in Montgomery’s Downcounty and Northeast consortia of high schools. The new one includes three schools with similar demographics — Gaithersburg, Watkins Mill and Seneca Valley — and compared the group of 11 high-poverty high schools with the district’s 14 lower-poverty schools.

In his letter, Starr wrote that the changing demographics of the county are beyond the school system’s control and “not simply a failure” to achieve economic integration.

Starr also said that the school system has “long embraced the tenet of avoiding minority group isolation” and challenged the report’s use of the word “segregated” as inconsistent with the data. He rejected the idea of a “flight” of white, Asian and middle-class students from the 11 high-poverty schools. White student enrollment has been trending down for 40 years, he wrote, as the county’s student population has become more diverse.

The analysis was released on the first day of the Montgomery County Council’s budget hearings, which include discussions about the school district’s $2.3 billion operating budget proposal.

It also comes in a year when the annual funding battle between school and county officials will unfold against the backdrop of Democratic primary races for the Board of Education, council and county executive. Dominating the debate will be the question of whether to exceed state-required minimum funding levels for the schools. The school system wants $51.7 million above the minimum — known as “maintenance of effort” — but any amount more than the minimum would raise the budget floor for coming years.

The report recommends that in light of the school system’s spotty record in narrowing the achievement gap, the council should more closely scrutinize the county schools’ budget to see how it will improve integration.

“It’s our obligation to address these disparities,” the County Council’s vice president, George L. Leventhal (D-At Large), said Tuesday.

Despite the criticisms in the Office of Legislative Oversight report, council members were careful not to directly disparage the school system. Council President Craig Rice (D-Upcounty), chairman of the council’s Education Committee, said the report deals with issues that “we have known for quite some time were pervasive.” But he said he met with Starr on Tuesday and had “a great conversation” on next steps.

Because school funding represents about half of the county’s operating budget, it is always a major topic at debates between candidates for county executive.

After five years of recommending budgets that kept schools at the state-mandated minimum, incumbent Isiah Leggett (D) proposed in his 2015 spending plan that Montgomery fund about half ($26 million) of the system’s request to exceed maintenance of effort. Leggett, who is seeking a third term, said at a debate in Silver Spring on Sunday that staying at the state minimum indefinitely would be a “recipe for disaster.” “If you want a school system that’s going to respond to the challenges of closing the achievement gap, then you’re going to have to spend over and above” maintenance of effort, he said.

Council member Phil Andrews (D-Gaithersburg-Rockville), one of Leggett’s two challengers, is an outspoken critic of the state’s minimum school-funding law. “It crowds out other parts of the budget,” he said.

Doug Duncan, a former three-term county executive who is running for the office again, pledged to work aggressively to change the funding law. “It’s a law that provides a disincentive to go above” maintenance of effort, he said.

Andrews and Leggett also favor changing the law.