American students are struggling with reading. And the country's education system hasn't found a way to make it better.

In fact, fourth and eighth grade reading scores on the National Assessment of Educational Progress essentially haven't budged in 10 years. That's causing some alarm, considering the number of reforms aimed at American schools over the past decade: stronger academic standards, more tests, stricter teacher evaluations and laws that discourage schools from promoting third graders if they can't read proficiently, to name a few.

"Reading has just been more or less plateauing, stagnating," said Peggy Carr, a leader of the assessments division for the National Center for Education Statistics, which administers the NAEP to a representative sample of students across the country every two years.

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How bad are the new reading scores?

Results of the 2019 NAEP, also known as the Nation's Report Card, showed elementary and middle school students scored worse in reading than they did two years ago.

Specifically, 35% of fourth graders were proficient in reading in 2019, slightly down from 37% in 2017 and barely up from 33% of such students considered proficient a decade ago, in 2009.

About 34% of eighth graders were proficient in reading this year, a drop from 36% in 2017 and only a tiny bit better than 32% in 2009.

To be clear, the national exams set a high bar for proficiency – higher than most state achievement tests. But they're the only consistent measure of how students nationwide are doing in core subjects over time. A sample of about 600,000 public and private school students in fourth and eighth grade took the reading and math exams in 2019. Their results were released Wednesday.

"Since the first reading assessment in 1992, there’s been no growth for the lowest-performing students in either fourth or eighth grade," Carr said. "Our students struggling the most with reading are where they were nearly 30 years ago."

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Why are reading scores so low?

So far, people can only offer theories.

An award-winning series last year by American Public Media reporter Emily Hanford investigated why many educators still don't know to give, or resist giving, children a firm foundation in phonics: the process of correlating sounds with letters or groups of letters.

Most schools also don't spend enough time having children practice reading fluency and developing their vocabulary, said Tim Rasinski, a literacy professor at Kent State University. Fluency helps kids understand words immediately and not use up so much mental capacity laboring on each one.

"Fluency requires different instructional methods than phonics," he said. "Practice is key."

Rasinski said he also thinks students are subjected to far too many tests, which leaves less time for instruction. And, he said, a lot of districts continue to adopt poorly designed reading curriculum.

Are national math scores any better?

In the short term, not really. But over 27 years, they've improved more than reading scores.

About 41% of fourth graders and 34% of eighth graders scored proficient in math in 2019. That's not significantly different from 2017.

Carr said the math scores are also about the same as a decade ago.

But since 1990, students at both grade levels have improved in math: Fourth graders this year scored 27 points higher on the 300-point exam compared with their peers in 1990. Eighth grade students posted an average score that was 19 points higher than in 1990.

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What else has happened to math and reading scores in the past decade?

The gap between the most- and least-competent students got bigger.

"Compared to a decade ago, we see that lower-achieving students made score declines in all of the assessments, while higher-performing students made score gains," Carr said.

This divergence in performance is one reason why average student achievement hasn't changed in a decade, Carr explained.

Is there any good news in the 2019 NAEP reading and math results?

Yes. Washington, D.C., students showed big gains in fourth grade reading and eighth grade math. In fact, D.C. Public Schools was the only large district to show test-score gains in three of the four assessments since 2017, Carr said.

Mississippi was the only other state to improve in fourth grade reading since 2017.

Detroit's public schools pulled out a big win in fourth grade math: Students scored 6 points higher there than in 2017.

Boys, Hispanic students and English language learners also improved in fourth grade math over the past two years.

Education coverage at USA TODAY is made possible in part by a grant from the Bill & Melinda Gates Foundation. The Gates Foundation does not provide editorial input.