For the first time since 1990, the mathematical skills of American students have dropped, according to results of a nationwide test released by the Education Department on Wednesday.
The decline appeared in both grades four and eight in an exam administered every two years as the National Assessment of Educational Progress and sometimes called "the nation's report card."
The dip in scores comes as the country's employers demand workers with ever-stronger skills in mathematics to compete in a global economy. It also comes as states grapple with the new Common Core academic standards and a rebellion against them.
Progress in reading, which has been generally more muted than in math for decades, also stalled this year as scores among fourth-graders flatlined and eighth-grade scores decreased. The exams assess a representative sampling of students on math and reading skills in public and private schools.
"It's obviously bad news," said Michael J. Petrilli, the president of the Thomas B. Fordham Institute, a right-leaning education policy group in Washington. "We don't want to see scores going in this direction."
"That doesn't mean we should completely freak out," he added. "This could be a one-time variation and maybe we'll see things come back next time, but if it were the beginning of a new trend, it would be quite disappointing and disturbing."
Education officials said that the first-time decline in math scores was unexpected, but that it could be related to changes ushered in by the Common Core standards, which have been adopted by more than 40 states. For example, some of the fourth-grade math questions on data analysis, statistics and geometry are not part of that grade's guidelines under the Common Core and so might not have been covered in class. The largest score drops on the fourth-grade math exams were on questions related to those topics.
The stagnating performance could also reflect the demographic changes sweeping U.S. schools and the persistent achievement gap between white students and minorities, as well as between students from poor families and their more affluent peers.
"It's not unusual when you see lots of different things happening in classrooms to first see a slight decline before you see improvement," said William J. Bushaw, the executive director of the National Assessment Governing Board, which sets policies and achievement levels for the tests.
About a quarter of public school students are Hispanic, compared with fewer than 10 percent in 1990. As a group, the scores of Hispanic students trail those of white students; this year, for example, 21 percent of Hispanic fourth-graders scored at a level deemed proficient or above on reading tests, compared with 46 percent of white students.
The proportion of African-American students in public schools has remained fairly stable, but an achievement gap with white students remains. On the fourth-grade reading tests this year, just 18 percent of black students were deemed proficient.
America's schoolchildren are also increasingly poor. Students from poor families often arrive at school with smaller vocabularies than students from middle-class or more affluent households, and are faced with challenges like hunger, homelessness and parents working several jobs, all of which can interfere with their learning in school and the academic support they receive at home — and ultimately their test scores.
Arne Duncan, the departing secretary of education, said schools should embrace the challenges of growing diversity. A study this week showed that student demographics can affect test scores. "We should be learning from each other and schools who are doing the best job with students with disabilities and English language learners and students living below the poverty line," Duncan said.
The average fourth-grade math score this year was 240 on a scale of 500, down from 242 in 2013, the last time the federal assessment results were released. The average eighth-grade math score was 282, down from 285 two years ago.
In reading, the average fourth-grade score of 223, compared with 222 in 2013, was not a statistically significant difference. The average eighth-grade score fell to 265 from 268.
No state or any of the 21 urban school districts that participated in the tests raised scores in both subjects and grade levels. But the District of Columbia repeated some of the strength it showed in 2013 by raising fourth-grade reading and math scores and holding eighth-grade reading and math scores steady. Kaya Henderson, the public schools chancellor, attributed the progress to strong teacher recruitment and training, preschool for 90 percent of the district's 4-year-olds and a new mandatory curriculum.
In Alaska, reading scores in both grades fell below the national average. However, the state's fourth-graders improved their scores from 2011, while eighth-grade scores remained steady.
In math, Alaska's fourth-grade scores fell below the national average but remained in line with 2011 scores. Meanwhile, eighth-grade students scored just one point under the national average. They had a similar average score in 2011.
As states have adopted the Common Core — guidelines for what students should know and be able to do between kindergarten and high school — many teachers have adjusted their curriculum and instructional methods, particularly in math. Students are asked to use math to solve real-life problems and find different ways to come at the same answer rather than simply repeating formulas.
Some educators suggested that some of the changes have sown confusion among teachers and students that could be reflected in the national test scores. "Right now, what's going on in many states is a wholesale change in math instruction," said Daniel Koretz, a professor of education at Harvard. "We don't know what's happening with that in classrooms."
A study released Monday showed that some items included in the national assessments are not covered by the Common Core before the grades in which they are tested.
"Knowing other kinds of math isn't going to help you unless you've been taught it," said Fran Stancavage, an author of the study. "The Common Core moves the sequence around, so there are lots of things that used to be taught before fourth grade that are now showing up in higher grades."
Randi Weingarten, the president of the American Federation of Teachers, linked the drop in test scores to recent educational policies as well as the economic downturn and its aftermath. "Of course we are disappointed" with the scores, she said. "But they should give pause to anyone who still wishes to double down on austerity and make competition, scapegoating teachers, closing rather than fixing schools, driving fear, and testing and sanctioning the dominant education strategies."
On Saturday, the Obama administration acknowledged that high-stakes testing had proliferated too far and urged states and school districts to cut down on the number of tests and make them more purposeful.
But with students taking so many other standardized tests, some educators said those who took the national exams, which were administered from January to March, may simply have had test fatigue. Protests about testing as well as decisions by some parents to opt their students out of testing could have influenced some students who took the national exams.
"If I was a student, it would be hard to know which ones to take seriously," said Chris Minnich, the executive director of the Council of Chief State School Officers, which represents state education commissioners. "I know at that point we were all talking about opting out and lots of different things were going on, and this was another test that showed up in classrooms across the country."
Alaska Dispatch News reporter Tegan Hanlon contributed to this article.