Numbers of adult students seeking high school equivalency diplomas have plunged more than 30 percent on Long Island and 40 percent statewide in recent years, according to a nonprofit group’s report that warns the drop-off could mean fewer workers are prepared for a challenging job market.

Experts on adult education attributed the decrease largely to more rigorous qualifying tests, based on Common Core academic standards.

Equivalency diplomas are awarded by the State Education Department to students, ages 18 and up, who pass qualifying tests after dropping out of regular high schools. Tests are free for students in New York.

The report by the Center for an Urban Future, released Thursday, found that the number of adult students in Nassau and Suffolk counties taking equivalency tests dropped from 2,031 in 2010 to 1,394 in 2015 — a decline of 31 percent.

Statewide figures over the same period dropped 46 percent, from 47,187 to 25,471.

“The number of New Yorkers taking and passing the high school equivalency exam has declined in virtually every corner of the state over the past five years, a troubling development at a time when today’s economy puts a premium on educational credentials,” the report by the Manhattan-based think tank said.

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Tom Hilliard, the senior researcher who wrote the report, said New York State should consider providing more funds to prepare students for equivalency testing and to computerize the exam. Hilliard declined to give specific dollar figures.

The State Education Department in February 2015 reported a decline in test-takers from 2012 to 2014, similar to that described in the urban center’s report. The department has not yet confirmed 2015 results, but a spokesman said Wednesday the agency is reviewing the center’s findings.

“We are doing everything possible with existing resources to encourage greater participation and to support better passing rates on the exam,” spokesman Jonathan Burman said.

Most of the drop-off in numbers reported by the urban center occurred between 2013 and 2014, when the state switched to a new equivalency exam — the Test Assessing Secondary Completion, or TASC, which is produced by a Minnesota company.

The exam requires about nine hours to complete and includes tests in science, mathematics, social studies, reading and writing.

In earlier years, the state used the General Educational Development exam, or GED, which fundamentally was a literacy test until it was upgraded in 2014. Albany’s switch to a more difficult assessment for adult learners was part of a nationwide movement by states toward higher standards.

Susan Giuliano, a Nassau BOCES teacher who instructs adults pursuing equivalency diplomas, said the transition from lessons in basic literacy to more advanced subjects had a profound impact on faculty and students alike.

“Students have to know science, they have to know history,” said Giuliano, now in her 16th year of teaching adult classes. “The complexity is just more challenging.”

Richie Martinez, 26, of Freeport, earned an equivalency diploma last month — and hung it in his living room — after more than three years of intensive studies in spoken English and academic subjects at a BOCES adult center in Levittown.

Martinez, who has a full-time night job as a restaurant manager, is continuing his morning studies at BOCES. He said he catches naps in between the two and is aiming for an eventual career in computer technology.

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“I realized I needed to educate myself,” Martinez said.

The state’s choice of tests also reflected financial concerns.

The GED had been sponsored for more than 70 years by a nonprofit organization, the American Council on Education.

In 2011, the council announced that it was forming a partnership with Pearson, a British-based testing corporation, to develop a more rigorous and computerized equivalency test.

The cost of the revamped assessment was pegged at $120 per student — more than five times the amount that New York State previously had paid the council for test and scoring materials, according to state officials.

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The current base cost of the TASC is $54, not including state and local administration fees, as listed on a test company website.

Leah Arnold, director of career, technical and adult education at Eastern Suffolk BOCES, said state funding of equivalency classes has remained flat in recent years, resulting in some student applicants being put on waiting lists.

“Each year, we serve fewer students,” Arnold said.