By Jennifer C. Kerr, Associated Press

WASHINGTON (AP) — American students have a math problem.

The latest global snapshot of student performance for 15-year-olds shows declining math scores in the U.S. and stagnant performance in science and reading.

"We're losing ground — a troubling prospect when, in today's knowledge-based economy, the best jobs can go anywhere in the world," said Education Secretary John B. King Jr. "Students in Massachusetts, Maryland, and Minnesota aren't just vying for great jobs along with their neighbors or across state lines, they must be competitive with peers in Finland, Germany, and Japan."

Math was a stubborn concern. "This pattern that we're seeing in mathematics seems to be consistent with what we've seen in previous assessments ... everything is just going down," said Peggy Carr, acting commissioner at the National Center for Education Statistics.

The 2015 Program for International Student Assessment (pdf), or PISA, study is the latest to document that American students are underperforming their peers in several Asian nations. The U.S. was below the international average in math and about average in science and reading. Singapore was the top performer in all three subjects on the PISA test.

More than half a million 15-year-old students in about 70 nations and educational systems took part in the exam, which is coordinated by the Paris-based Organization for Economic Cooperation and Development, or OECD.

Here are the main things to know about PISA:

U.S. SCORES AND RANKINGS

Not so encouraging.

The test is based on a 1,000-point scale. Among the findings:

-In math, the U.S. average score was 470, below the international average of 490. Average scores ranged from 564 in Singapore to 328 in the Dominican Republic.

-In science, the U.S. average score was 496, about the same as the international average of 493. Average scores ranged from 556 in Singapore to 332 in the Dominican Republic.

-In reading, the U.S. average score was 497, around the same as the international average of 493. Average scores ranged from 535 in Singapore to 347 in Lebanon.

Average scores in math have been on the decline since 2009. Scores in reading and science have been flat during that same time period. Across the globe, American students were outperformed by their counterparts in 36 countries in math; 18 countries in science and 14 countries in reading.

SO, WHAT IS GOING ON WITH MATH?

Andreas Schleicher, director for education and skills at OECD, says high-performing countries do really well in math in three things: rigor, focus, and coherence.

For example, he says, many high-performing countries will teach a lot less but focus at much greater depths, particularly when you look at East Asia, Japan and Singapore.

"Students are often good at answering the first layer of a problem in the United States," said Schleicher. "But as soon as students have to go deeper and answer the more complex part of a problem, they have difficulties."

THE BRIGHT SPOT IN THE U.S.

All eyes are on Massachusetts.

The Bay State participated as an international benchmark in PISA and received scores separate from the United States as a whole. Students in the state performed exceptionally well.

Massachusetts's average scores were higher than the U.S. and the international average scores in science, math and reading. And for reading, Massachusetts was a top-tier performer, just behind Singapore and tied with Hong Kong and Canada.

Mitchell Chester, commissioner of Massachusetts public schools, says the state has spent two decades implementing higher standards, tests of student performance and money to support poorer districts.

"We measure our progress against that standard," he said in an interview. "We hold people accountable for those results and we support them to reach the results financially."

WHAT PEOPLE ARE SAYING

—"What do the PISA high-performing nations do differently than the United States? They invest in their students. They fully fund all of their schools, regardless of the ZIP code or community they are in." — National Education Association President Lily Eskelsen García

—"It's a combination of high standards, useful assessments and investing in our educators with high-quality curricula and professional development that can make a really meaningful impact. When you look at countries, and states, and schools that have that blend ... you see real improvements." — Jon Schnur, executive chairman of America Achieves.

OTHER FINDINGS

Globally, gender differences in science tended to be smaller than in reading and math. But, on average, in 33 countries and economies, the share of top performers in science is larger among boys than among girls. Finland was the only country where girls were more likely to be top performers than boys.

Across OECD countries, on average, the gender gap in reading in favor of girls narrowed by 12 points between 2009 and 2015.

ABOUT THE TEST AND COMPARISONS

The PISA test is conducted every three years. Schools in each country are randomly selected. OECD says student samples are drawn from a broad range of backgrounds and abilities.

Another international test, known as the Trends in International Mathematics and Science Study, or TIMSS, had similar international comparisons with Asian countries solidly outperforming American students. That test, though, administered to younger students had eighth graders in the United States improving their scores in math, up nine points. Scores for science, however, were flat. In fourth grade, scores were unchanged in math and science.

To Learn More:

PISA 2015: Results in Focus (Organization for Economic Cooperation and Development) (pdf)