A new report shows some U.S. school children are performing at their highest level in math, while progress in reading is mixed.

In a report Tuesday, the National Assessment of Educational Progress said students in the fourth and eight grades are doing their best ever in math. It said that on a 500-point scale, both grades scored about one point higher in math this year compared to 2009. It noted the scores are more than 20 points higher compared to 1990.

It said the average fourth-grade reading score this year remained unchanged from 2009, while the average eighth-grade reading score was one point higher than in 2009.

The U.S. Department of Education described the scores as a reason for both concern and optimism. Education Secretary Arne Duncan said the results continue a “pattern of modest progress.” In a statement, he said that although achievement is up, it is not at a fast enough rate for the nation's children to compete in the “knowledge economy” of the 21st century.

Schools have been required under the No Child Left Behind act, which became law in 2002, to meet certain achievement standards, although President Barack Obama this year announced plans for greater flexibility over how students are taught.

Critics say the law is too focused on standardized student testing, penalizing even high-performing schools if some students fall short on performance examinations. In September, Mr. Obama praised his predecessor, George W. Bush, for trying to improve the education system, but said the law had numerous “flaws” and that changes were overdue.

The No Child Left Behind law requires every student to be proficient in math and reading by 2014.

The Obama administration plan grants waivers to states that promise to meet even more rigorous standards. Mr. Obama said the plan was needed after Congress repeatedly failed to address flaws in No Child Left Behind.