Maryland fourth- and eighth-graders scored slightly lower in math on a national test than two years earlier, though the state's pass rates still remain among the best in the country, according to data released Thursday.

"I was pleased that we are trending above the national average in all areas," said state schools Superintendent Lillian M. Lowery. She acknowledged the state has had more difficulty with math achievement.

Maryland's reading scores rose in both grades on the National Assessment of Educational Progress, one point in fourth grade and three points in eighth grade. The math scores dipped by two points in fourth grade, the largest drop in the nation, and one point in eighth grade.

Federal education officials cautioned that they cannot say the scores in Maryland are significantly different from those in 2011. The test, which has a margin of error, is given to a sample of students, so officials cannot be sure that if they gave the test to every student, the differences would remain.

Since 2003, the state has ranked among the top in performance and in progress on what is known as "The Nation's Report Card," considered among the most reliable long-term measures of achievement.

But this year's slight dip in math diverged from the overall national trend, which showed improvement in both math and reading. There were particularly large spikes in achievement in several states, including Tennessee, Hawaii and the District of Columbia.

"I am surprised to see some big gains in some states and some significant gains in eighth-grade reading, which we have not seen in the past," said Jack Buckley, commissioner of the National Center for Education Statistics.

U.S. Education Secretary Arne Duncan, who described overall performance as modest, credited those particularly large gains in some states to the introduction of the new, more rigorous "Common Core" standards and other initiatives the Obama administration has promoted, including new teacher evaluations.

The eight states that were slightly ahead of Maryland in their implementation of the Common Core standards showed improvement in reading or math or both. None had a decline in scores.

While Maryland ranks well above the national averages, the state and national scores still point to lackluster achievement compared to students in other countries. More than half the students in every grade and subject fail the test.

In Maryland, 46 percent of fourth-graders and 38 percent of eighth-graders scored proficient or advanced in math, 4 percentage points higher than the nation in both grades. Only 44 percent of fourth-graders and 43 percent of eighth-graders achieved proficiency in reading, compared to 34 percent and 35 percent, respectively, in the nation.

Gaps in achievement between black and white students in Maryland remain among the largest in the country.

Jason Botel, executive director of the policy, research and advocacy nonprofit MarylandCAN, said "those who hide behind the 'Maryland's Schools are #1' claim are putting hundreds of thousands of children and indeed our whole state at risk and are impeding our ability to pass the reforms needed to ensure all children have access to high-quality public education."

State officials said they are not worried by the scores. They said student performance in math will improve in the next several years.

They point to Maryland's long-term improvement over the two decades the test has been given. And they say that while scores in fourth-grade math slipped slightly, 13 percent of students scored in the advanced category, one of the highest results in the nation.

The state's students have scored consistently lower in math than in reading on both the annual state tests and the NAEP. Lowery blamed the way in which math has been taught for years in the state. Teachers were told to cover a wide range of material every year, touching on many concepts.

This year, teachers have changed their approach to be in line with the Common Core standards, adopted by 46 states and the District of Columbia. They now teach far fewer concepts each year, but at greater depth.

"Teachers can have time to focus on those anchor standards," Lowery said. "I think that is going to make a huge difference."

Duncan said states should invest more in early education so that students come to kindergarten equally prepared to learn. Too much time and effort, he said, is spent trying to catch up students who did not attend early education programs.

Maryland's Democratic candidates for governor have called for expanding prekindergarten.

liz.bowie@baltsun.com