In a new Pew Research Center report, only 29% of Americans rated their country’s K-12 education in science, technology, engineering and mathematics (known as STEM) as above average or the best in the world. Scientists were even more critical: a companion survey of members of the American Association for the Advancement of Science found that just 16% called U.S. K-12 STEM education the best or above average; 46%, in contrast, said K-12 STEM in the U.S. was below average.

Standardized test results largely appear to bear out those perceptions. While U.S. students are scoring higher on national math assessments than they did two decades ago (data from science tests are sketchier), they still rank around the middle of the pack in international comparisons, and behind many other advanced industrial nations.

One of the biggest cross-national tests is the Program for International Student Assessment (PISA), which every three years measures reading ability, math and science literacy and other key skills among 15-year-olds in dozens of developed and developing countries. The most recent PISA results, from 2012, placed the U.S. at an unimpressive 35th out of 64 countries in math and 27th in science. Among the 34 members of the Organization for Economic Cooperation and Development, which sponsors the PISA initiative, the U.S. ranked 27th in math and 20th in science.

Younger American students fare somewhat better on a similar cross-national assessment, the Trends in International Mathematics and Science Study shows. That study, known as TIMSS, has tested students in the fourth and eighth grade every four years since 1995. In the most recent tests, from 2011, seven countries (out of 50 total) had statistically higher average fourth-grade math scores than the U.S., while six countries had higher average science scores. In the eighth-grade tests, six out of 42 countries had statistically higher average math scores than the U.S., and eight had higher science scores.

Another long-running testing effort, the National Assessment of Educational Progress (a project of the federal Education Department), has found that U.S. students have made substantial math gains since 1990. A National Science Foundation report notes that, while eighth-grade scores “show a continuous upward trend, fourth-grade scores leveled off in recent years.”

The average fourth-grade NAEP math score in 2013 was 242 (on a 0-to-500 scale), versus 213 in 1990, but has moved up only 2 points since 2007. The average eighth-grade score was 285 in 2013, compared with 263 in 1990; it’s moved up 4 points since 2007.

Looked at another way, the 2013 NAEP rated 42% of fourth-graders and 36% of eighth-graders as “proficient” or “advanced” in math. While far fewer students now rate at the lowest performance level (17% of fourth-graders and 26% of eighth-graders in 2013 versus 50% and 48%, respectively, in 1990), improvement in the top levels has slowed considerably since 2007.

NAEP also tests U.S. students on science, though not as regularly. The 2013 results haven’t yet been released, and a major revision in 2009 means results before then aren’t comparable. Still, we can say that science performance among eighth-graders improved slightly between 2009 and 2011, with the average score rising from 150 to 152. In 2011, just 32% were rated proficient or better, while a third were rated “basic” and 35% were below basic.