Experts have long decried U.S. student performance in math and science, but new data suggests cause for cautious optimism. A nationwide report on student achievement in science, released Thursday by the U.S. Department of Education's National Assessment of Educational Progress, showed that fourth- and eighth-graders have improved since 2009, the last time such data was collected for both grades. The gap between racial and ethnic groups has narrowed as well. Twelfth-graders did not see any change in performance, however, and many of the other gains were modest.

"I am encouraged that we see some progress in grades four and eight­—it’s not dramatic but it is significant,” says David Evans, executive director of the National Science Teachers Association (NSTA), who was not involved in producing the report. “It’s also encouraging that we see a shrinking of the [racial] achievement gap in some areas,” he says, but adds, “We obviously still have a long way to go.”

The “Nation’s Report Card: 2015 Science” was based on a nationally representative sample of 115,400 fourth-graders, 110,900 eighth-graders and 11,000 12th-graders in both public and private schools. Additional data was provided voluntarily by 46 states and the Department of Defense (DoD) school system for fourth and eighth grades. The report assessed students’ knowledge of physical and life science, as well as Earth and space sciences on a scale of 0 to 300, and classified the students into three achievement levels: basic, proficient and advanced.

The results showed the number of both fourth- and eighth-graders scoring at or above “proficient” level rose by four points compared with 2009. In addition, the gap between different racial or ethnic groups narrowed, decreasing by two points between whites and blacks and four points between whites and Hispanics. In terms of gender there was no statistically significant difference between boys and girls at grade four—but by grade 12 male students scored an average of five points higher than girls, a gap that remained unchanged from 2009.

Twelfth-grade achievement in math and science has stayed stagnant since 2009, however, and absolute performance across the board remains poor, according to the new report. In 2015 just 22 percent of 12th-graders scored at the “proficient” level. The situation was slightly better for fourth- and eighth-graders, 38 percent and 34 percent of whom performed at this level, respectively.

At the state level, 18 states’ scores for fourth grade improved since 2009, and one state, Delaware, reported a decrease. Four states or jurisdictions—Arizona, Tennessee, Georgia and the DoD schools—saw greater improvements than the national average.

A total of 24 states reported improved scores in eighth grade in 2015 compared with 2009 and 2011, and no states’ scores decreased. Three states—Utah, Tennessee and Nevada—improved more than the national average since 2009. (Data for eighth-graders was available from 2011 as well as 2009 and 2015).

Experts were uncertain as to what might be behind the gains in fourth and eighth grades. “That is the 64-million-dollar question,” Bill Bushaw, executive director of the independent National Assessment Governing Board, said in a press briefing. He pointed to increased hands-on learning as one possible explanation, but noted that this was merely a correlation and does not necessarily show cause and effect.

“We are happy to see continued progress in closing achievement gaps in the lower grades,” James Brown, executive director of the STEM Education Coalition, a nonprofit group that lobbies on behalf of science and math education, said in an e-mailed statement. “Many states are in the process of adopting new teaching frameworks in science and the jury is still out on that process right now.” (STEM stands for science, technology, engineering and mathematics).

A consortium of 26 states as well as education and science groups in 2013 released a set of content standards known as the Next Generation Science Standards. “I’d like to think that we’re beginning to see a little progress” due to these standards, NSTA's Evans says. But Peggy Carr, acting commissioner of the National Center for Education Statistics, noted in the briefing that when she and her colleagues looked at the performances of states that had adopted those standards, “there was absolutely no pattern.”

As for why the 12th-graders showed no improvement, Evans suspects it may simply take longer to implement changes at the high school level. Another possible explanation, Carr says, may be that high school graduation rates have increased since 2009, so the 12th-grade sample may contain a wider range of students.

“The 2015 Science Report Card data show that all students are making progress, particularly fourth and eighth grade,” Carr said, adding, “This is exactly what we’d like to see.” But “there’s still much progress to be made, because these gaps are still large, particularly for racial or ethnic groups.”