NEW YORK — Eighteen private Jewish schools run by New York City’s politically powerful Hasidic community deprived thousands of students the required secular education in English, math, science and social studies that they need to function successfully outside their religious enclaves, according to findings from an eight-year investigation by New York City school officials.

The investigation — which critics say was long delayed because of politics — concluded that many of the religious schools, or yeshivas, were not providing “substantially equivalent instruction” in core subjects as do public schools — as mandated by state law.

In a letter to at least one school, NYC schools Chancellor David Banks expressed concern that students were not being instructed in key subjects “sufficient to prepare them for their futures.”

A review of more than two dozen yeshivas, which receive hundreds of millions in public funding, determined that only seven of those schools were in compliance with state rules.

The probe was sparked by complaints by a former student who said he was not provided the schooling necessary to navigate the outside world. He would later form a group called Young Advocates for Fair Education, which got the city’s Department of Education to launch an investigation in 2015.

“We hope that the completion of this investigation compels the city and Mayor Eric Adams to act on behalf of thousands of students who are being deprived of their right to a sound basic education,” said the group’s executive director, Beatrice Weber.

The investigation was conducted in fits and starts, as Hasidic leaders used their political muscle to push back against any intrusions into their community, which is concentrated in the Brooklyn neighborhood of Williamsburg.

Hasidic Jews comprise one movement of Orthodox Judaism. And while the roughly 200,000 Hasidic Jews in New York City represent just a fraction of the city’s Jewish population, they have amassed considerable influence within the city’s power structure because of the community’s penchant for voting as a bloc.

Yeshivas, many of them small, play a central role in preserving Hasidic traditions and religious orthodoxy. In some schools, instruction is conducted primarily in Yiddish — in violation of state law mandating that instruction be done in English. The investigation found that sometimes English was not taught at all. The typical school day was spent on teaching the Torah and Talmud. In some cases, yeshiva administrators refused requests to allow city school officials to do follow-up visits.

A spokesperson for Parents for Educational and Religious Liberty in Schools, which has defended the Hasidic schools under fire, could not be reached on Saturday, a day of Sabbath for many Jews.

Richard Bamberger, a representative of the group, told the New York Daily News on Friday that parents send their children to yeshivas because of the moral and religious approach taken by the schools.

“They will continue to do so, regardless of how many government lawyers try to insist that yeshiva education is best measured by checklists they devise rather than the lives yeshiva graduates lead,” he told the New York Daily News.

City school officials said the bulk of schools it visited were cooperative, while a small number of schools were less so.

“For any school found to not be substantially equivalent,” NYC schools spokesperson Nathaniel Styer said in a statement, “the DOE stands ready to support the school to becoming substantially equivalent.”

The schools that failed to provide the necessary instruction must draft a remediation plan and have as long as two years to put it in place.

“Our goal is to educate children, not punish adults,” Styer said.

The completion of the investigation comes amid a push to strengthen oversight of the state’s 1,800 private and religious schools, following a New York Times investigation published last fall that exposed how students at Hasidic schools were denied basic education in crucial subjects.

The new state rules were pared back by a judge earlier this year after a lawsuit was brought by ultra-Orthodox Jewish schools. The judge ruled that parents cannot be required to pull their children from private schools that fail to meet state-designated standards.

Weber said she worries about how the remediation plans will be implemented.

“We’re very concerned about what this will look like, what this will mean and how much guidance these schools will get,” Weber said in an interview Saturday. “We cannot just let years go by with the schools claiming they’re trying to improve. There needs to be real deadlines.”

It is unclear how many students attend the schools that were reviewed, but they certainly number in the thousands.

What’s more, there are scores of other Hasidic yeshivas that were not part of the investigation, Weber said, so there could be other schools that are noncompliant but have yet to be subjects of complaint.

Weber acknowledged that many of these yeshivas are indeed complying with state standards and are doing exceptional jobs in giving their students the education that will help serve them later in life.