In this file photo, a math teacher helps an eigth-grader understand algebra. (Astrid Riecken/For The Washington Post)

When it comes to math, U.S. high school students are falling further behind their international counterparts, according to results released Tuesday of an ongoing study that compares academic achievement in 73 countries. And the news is not much better in reading and science literacy, where U.S. high schoolers have not gained any ground and continue to trail students in a slew of developed countries around the globe.

In the latest Program for International Student Assessment (PISA) measuring math literacy in 2015, U.S. students ranked 40th in the world. The U.S. average math score of 470 represents the second decline in the past two assessments — down from 482 in 2012 and 488 in 2009. The U.S. score in 2015 was 23 points lower than the average of all of the nations taking part in the survey.

Although 6 percent of U.S. students who took the test had scores in the highest proficiency range, 29 percent of U.S. students did not meet the test’s baseline proficiency for math.

In reading and science, U.S. students were basically treading water, their rankings relatively unchanged from previous years. The United States ranked 25th in science literacy and 24th in reading literacy. Singapore topped all nations in all three categories. China, Japan, Korea, Canada, Switzerland, Estonia, Australia and New Zealand were among the other top-performing countries.

U.S. math literacy on the international PISA exam in 2015 was below the international average. (National Center for Education Statistics)

Begun in 2000 and conducted every three years, the PISA was created to measure the performance of 15-year-old students in science, math and reading literacy in the 35 industrialized countries of the Organization for Economic Cooperation and Development (OECD). The number of countries taking part has expanded to 73. Approximately 540,000 students took the assessment in 2015, including 5,700 U.S. public and private-school students.

The PISA results come on the heels of another international study of fourth- and eighth-graders — the Trends in International Mathematics and Science Study, or TIMSS — that showed American students trailing their Asian peers in math and science achievement.

Education experts differ about what the new PISA results mean for U.S. standards of ­learning.

U.S. student performance in the most recent assessment should serve as a “Sputnik moment” for U.S. leaders and educators, said Marc Tucker, president of the National Center on Education and the Economy. Tucker pointed specifically to the results from Chinese students and said that the United States should study how a country that is still relatively poor can outperform students in the wealthiest country in the world.

“We’re living in a world that is highly integrated,” Tucker said. “And the United States cannot long operate a world-class economy if our workers are, as the OECD statistics show, among the worst-educated in the world.”

Tucker said that he would advise the incoming Trump administration to “focus like a laser” on the data provided by these results as it addresses education decision-making.

“Donald Trump as candidate basically staked his candidacy on the plight of industrial workers in the United States,” he said. “The Chinese workers are vastly better educated than the typical American worker and willing to work for one-fifth of what the equivalent American workers are willing to work for. That is a proposal for economic disaster.”

Tucker said China’s investment in teachers is key to the country’s success in math, science and reading literacy.

“They have redesigned their schools to take advantage of very highly educated and trained teachers,” he said. “They have organized their schools so that teachers work together in teams in a very disciplined way to get better and better at teaching and to constantly improve the performance of their students.”

But other experts dismiss the value of the PISA results and say they ignore integral aspects of education.

“The results basically tell us how well these students took the test, that’s all,” said Yong Zhao, a professor in the School of Education at the University of Kansas. “Whether that performance has anything to do with real life or the quality of education, we don’t know. There’s no other evidence. We don’t have to really jump on this, let alone try to borrow policies or ideas from other places.”

Zhao said he views the PISA as a “joke” and thinks that similar international test rankings should be scrapped.

“I disregard all these tests because no test actually measures exceptionality,” he said. “But an economy, especially today, is driven by individual exceptionality. Entrepreneurship, entertainment, inventiveness, creativity — no tests can measure that.”

Calling the PISA results “sobering news,” U.S. Education Secretary John B. King Jr. acknowledged that U.S. students are well behind their peers.

“We’re losing ground — a troubling prospect when, in today’s knowledge-based economy, the best jobs can go anywhere in the world,” he said. But King pointed to Massachusetts, where students excelled on the PISA test, as an example of how states can get education right.