WASHINGTON — US youngsters are scoring better in mathematics, but progress in reading skills is mixed, a national yardstick of student achievement released Tuesday showed.

In the fourth and eighth grades, the average math score in 2010 was one point higher than in the previous year, said the National Assessment of Educational Progress, which has been monitoring the performance of American pupils since 1969.

Looking back two decades, fourth graders -- typically nine-year-olds -- scored 28 points better than in 1990, and eighth graders -- around 13 years old -- improved 21 points in their math results.

But reading performance among fourth graders in 2010 was unchanged from a year earlier, and up only four points from 1992. In the eighth grade, the average reading score was up one point from 2009 and five points from 1992.

"We applaud all students and teachers for their impressive and consistent gains in math achievement," said David Driscoll, chairman of the National Assessment Governing Board, in a statement.

But he added: "While we are encouraged by the continued progress in eighth-grade reading, we remain concerned about the stalled performance in fourth-grade reading."

Students of Asian heritage did best in both subjects, with 64 percent in the fourth grade and 58 percent in the eighth grade scoring proficient or better in math, and 50 percent and 49 percent doing likewise in reading.