Utah's eighth-grade students scored an average of 166 on a 300-point scale, 13 points above the national average .
Fourth-graders in Utah scored 160 on the science test, seven points above the national average, to give them the No. 9 rank.
Scores at those grade levels were improved from the last time the science test was administered — 2011 for eighth grade and 2009 for fourth grade — climbing five points and six points for eighth grade and fourth grade, respectively.
"This is terrific news," Utah Board of Education spokesman Mark Peterson said, "We are the only state with at least half the students proficient in science."
The National Assessment of Educational Progress, or NAEP, tests a representative sample of students in most states to generate a national snapshot of student learning.
Math and reading tests from 2015 were released last year and similarly showed Utah students outperforming the national average and maintaining the state's scores despite declines across the country in those subject areas.
"I think this bodes very well for STEM subjects in Utah schools," Peterson said, referring to an acronym for science, technology, engineering and mathematics. "We are doing a happy dance here."
In addition to overall scores, the NAEP measures students' performance relative to grade-level expectations.
In Utah, 45 percent of fourth-graders scored at or above a proficient level, compared to 37 percent nationally, and 50 percent of eighth-graders met proficiency levels, compared to 33 percent nationally.
Utah also scored above the national averages for most demographic groups, including low-income students in fourth and eighth grades.
Among Utah's eighth-grade students, American Indians scored two points below the national average, and Asians/Pacific Islanders scored six points below the national average.
Peterson said that result could be due to relatively high numbers of Pacific Islanders in the state, who traditionally underperformed compared to their white peers, compared to larger Asian populations throughout the rest of the country and who tend to score near or better than white students.