The U.S. military is seeing lower scores on its Armed Forces Qualification Test.

At Texas State Technical College, a two-year college based in Waco, students increasingly have to take a basic math class alongside their college-level courses to get ready for careers in welding, heating and air conditioning, and manufacturing.

And at selective four-year colleges, professors complain that students have lost their reading and writing stamina.

New national test results for 12th graders, released this month, showed significant declines in students’ math and reading abilities since 2019, results that are now being felt in college and the labor market.

“My students now, they leave high school and don’t have the capacity to read a lengthy 25-page article. They don’t know what to do with it,” said Deepak Sarma, a humanities professor at Case Western Reserve University, where the average reported SAT score is between 1440 and 1520. Dr. Sarma recently counseled a student daunted by a dense academic article, suggesting basic tactics like printing it out in order to highlight and underline key passages.

On the national test, students’ reading scores were the worst in three decades, and math scores were the lowest since 2005.

The scores are at least partially explained by the pandemic and school closures. But they also reflect broader societal changes, including an increase in time spent in front of screens for both young people and adults. The decline was primarily driven by lower-scoring students, who have been losing ground for a decade.

The results have vast consequences for a generation of students, the U.S. economy and the country, which already ranks 28th in the world for math, behind Japan, Canada, the United Kingdom, Germany and nearly every other major industrialized democracy.

“The U.S. is an example of frogs in the boiling water when it comes to talent,” said Jamie Merisotis, chief executive of the Lumina Foundation, which is focused on higher education and work force credentials. Because the United States has a large and diverse economy, he said, “it’s harder to see when the rest of the world is catching up.”

The world’s highest-performing countries not only produce students who outscore the brightest American students at the top. They also manage to lift far more students up to a base level of skill — something some experts believe is only going to become more important in a world of artificial intelligence.

“A.I. can do the first draft of the memo or solve the math equation,” Mr. Merisotis said. “It is the worker who needs to understand what they are reading, be able to ensure it is accurate and decide what to do next.”

Fundamental reading and math skills are needed for a wide range of jobs, employers and industry leaders said, from health care workers calculating medication dosage and documenting patient care to truck drivers navigating the nation’s highways.

“There is a lot of math that you don’t necessarily think about,” said Lindsey Trent, president of the Next Generation in Trucking Association, a trade group, who said that even entry-level drivers must be able to calculate weight distributions on their trucks and estimate mileage without exceeding federal limits for hours on the road.

Randall Stephenson, who was the chief executive of AT&T from 2007 until 2020, said that during his tenure, the company screened candidates for math and other basic skills, which often required going through a large pool of candidates to make a single hire.

“Anybody who is going to be doing basic customer interactions — working on billing issues and rates, what is the right rate plan for a customer? — simple basic math is absolutely required,” Mr. Stephenson said.

He has now turned his attention to education. He and his wife funded an intensive math tutoring program for high school students in the Oklahoma City area who are in the bottom 25th percent of their class.

Even as scores have fallen, there are few indications that dramatically more students are dropping out. Nationally, 87 percent of students graduate high school on time. Only about 5 percent of young adults don’t have a degree or a high school equivalency diploma.

Instead, students are graduating with fewer skills, leaving them less prepared for college and beyond.

At Texas State Technical College, students who arrive needing extra help are placed into a fundamentals class, to be taken alongside their college-credit courses. The school tries to emphasize why academics are necessary for each line of work, said Cledia Hernandez, a vice chancellor. Fractions, for example, are essential for pipe fitting, where a job may come down to “a one-sixteenth of an inch in a pipe.”

Nationally, there has been little political will from either party to meaningfully lift student outcomes. While Republicans focus on giving parents more education choices, including helping families pay for private school and home-schooling, Democrats have spent political capital on what they see as root causes for challenges at school, like poverty and mental health.

One of the largest-ever federal investments in education, $122 billion for pandemic recovery during the Biden administration, did little to raise scores across the board, in part because it required districts to use just 20 percent of their money on academic recovery.

About 62 percent of recent high school graduates immediately enroll in college. The rest make their way into the work force, hoping to make a living without taking on debt.

They can make about $23 an hour working at an Amazon warehouse, or work to build up their skills and experience in the construction industry, where a crane operator might bring in anywhere from $45,000 to $80,000 a year.

“I’ll be really honest — this industry is less concerned with test scores than any other industry,” said Jackie Roskos, director of the Specialized Carriers & Rigging Foundation, which works with crane and rigging companies focused on specialized transportation projects, such as replacing parts of a bridge.

She said companies care far more about building on-the-job skills and safety experience than any test score. “It’s so highly skilled and they need so much experience,” she said. “It’s not because they can’t read and do math.”

Still, experts said, many workers become limited when they try to climb the ladder and move into higher-paying roles.

“Yes, you can probably get an entry-level warehouse job with very limited math and reading skills. But then what? And whose responsibility is it to help that individual?” said Jeff Bulanda, vice president of the ASA Center for Career Navigation at Jobs for the Future, a nonprofit that works to bridge education and the work force.

“Employers need to now step in,” he said, “because our educational system failed.”

Guild, a talent development company, works with companies like Target, Chipotle and Tyson Foods to help their employees get a high school equivalency diploma, and master basic math and English skills.

In the last two years, the company has gotten more requests for “foundational learning,” which includes math and helping non-English speakers become more comfortable with the language, Guild’s chief executive, Bijal Shah, said. “It goes back to things like customer service,” she said.

The U.S. military, the nation’s largest employer, is also taking on training of its own. The Army and the Navy offer academic prep courses aimed at helping recruits with lower test scores become eligible for a wider range of jobs across the military, a Pentagon official said.

At least part of the solution may lie in helping students get ready to work before they even leave high school.

Wellstar Health System, which operates 11 hospitals in Georgia, partners with several high schools to produce a pipeline of new talent. Students can work part time at Wellstar while still in high school, earn a health care certificate and graduate with a job offer.

The company sees it as a win-win, helping students establish stable careers while also addressing a work force shortage.

“Yes, the learning gaps are real,” said Laura Dannels, Wellstar’s chief talent officer. “But rather than seeing that as a barrier, we see it as a call to action.”