AMNA NAWAZ: Math and reading scores have dropped to their lowest levels in more than two decades among high school seniors.

William Brangham reports on new test scores that have many educators and other experts concerned.

WILLIAM BRANGHAM: That's right, Amna.

These scores come from the latest so-called Nation's Report Card, which is put out by the National Assessment of Educational Progress, and it shows that student achievement has continued to decline significantly since the pandemic.

Among high school seniors, the average reading score last year was the lowest since the assessment began in 1992.

What's worse, nearly a third of seniors did not have the basic reading skills needed to find the details in a given text to understand its meaning.

Average math scores also slipped to their lowest levels since 2005.

There are many theories about what is going on here.

And so, to explore some of that, we are joined by Thomas Kane.

He's a professor of education at Harvard's Graduate School of Education.

Thomas Kane, thank you so much for being here.

Somewhat of a broad question for you, but what is your best assessment as to why these scores are so low and continuing to decline?

THOMAS KANE, Harvard Graduate School of Education: So, first of all, these latest results are not surprising, unfortunately.

Our research center has been tracking trends at -- for individual districts around the country for the last three or four years.

What is new is the degree to which these losses are concentrated among the lower-achieving students.

So the 10th percentile student in the U.S. has lost about two grade equivalents since 2015.

That's a large loss.

And it'll be equivalent to about 5 percent of lifetime earnings.

So this would have impacts on future income inequality if we don't reverse it.

WILLIAM BRANGHAM: So can you run us through what the sort of principal theories are as to why we are in the state we're in?

THOMAS KANE: There are three hypotheses to explain what's been happening.

Number one is, there's been a decline in focus on test-based accountability since the No Child Left Behind act expired in 2015.

But the two other hypotheses are the rise in social media use, which is concentrated among lower-achieving students -- by the way, a number of European and Asian countries are seeing the same widening that we are.

And a third possibility is the rise in student absenteeism, which spiked during the pandemic, but remains high.

WILLIAM BRANGHAM: I want to pick apart a couple of those, one of them in particular.

We spoke earlier with a woman named Adeola Whitney.

She's the CEO of a group called Reading Partners.

And, as the name suggests, she points to that being a very critical skill that's at issue here.

Let's hear what she had to say.

ADEOLA WHITNEY, CEO, Reading Partners: There's research that shows that in order for kids to be better at reading, they have to practice reading.

They need to read more often.

But when we look at early grades like K through 2, if a child is already struggling to read, reading more if they're not able to read is a challenge in and of itself.

So is there someone at home that -- who can read to them to help build the vocabulary and their comprehension skills?

WILLIAM BRANGHAM: Do you agree with that assessment, that, one reading is so critical to a student's attainment educationally, but also then how do we address that gap?

THOMAS KANE: So, I agree.

Actually, reading and math has long term consequences for students' earnings and educational attainment and so forth.

And I also agree that early-grade reading is critical.

But what we're seeing in these numbers is that the problem extends well beyond early grades, that there's been a large decline in eighth grade and in 12th grade reading achievement as well.

And so, while we work on K to 2, we need approaches to helping the students who are already past grade two to recover.

If we don't, they will suffer in the long run.

WILLIAM BRANGHAM: You mentioned this issue of accountability and testing.

And there are many educators and experts in the field who believe that that whole era of testing was a failure in and of itself, that it didn't really help students, and that it was a diversion from other issues.

But you believe that a better testing regimen would help?

THOMAS KANE: So I think, actually, that's misreading the facts of what's happened over the last 30 years.

Most people don't realize that, between 1990 and 2015, there were substantial improvements in math and reading achievement.

And it's clear that test-based accountability is not sufficient to produce the continued improvements we need, but once states started taking their foot off the pedal in 2015 focusing on test-based outcomes, we see the result of declining achievement, especially at the bottom, where a lot of the accountability pressures were being felt.

But I think recovering from this is not just about the old debate about test-based accountability.

It's about finding effective ways to lower absenteeism.

And we have got to learn as quickly as possible, what are the effects of the cell phone BANS that a number of states and districts have implemented in the last couple of years?

If it is social media, then we ought to be seeing positive effects of cell phone bans.

If we don't, that will be important to know too.

But I think the solution now is not just about test-based accountability.

It's about states piloting ways to lower absenteeism and, as they have already done, piloting ways to lower social media use, and then us learning from those efforts, what are the impact on student achievement, so we can spread what worked.

WILLIAM BRANGHAM: All right, that is Thomas Kane at Harvard's Graduate School of Education.

Thank you so much for being here.

THOMAS KANE: Thanks, William.