Scores on the “nation’s report card” were more or less flat — but those numbers don’t tell the whole story.

The gap between high-achieving and low-achieving students appears to be widening, according to National Assessment of Educational Progress test results released Tuesday.

“It certainly is an alarm bell,” said Tom Loveless of the Brookings Institution, a Washington, D.C.-based nonprofit think tank, in an interview with the Washington Post. “It’s something to watch and monitor, especially if this persisted.”

Nationally, only eighth-grade reading scores improved from 2015, the last time students took the NAEP. But that was because high-achieving students fared better in 2017, while lower-achieving students held their ground.

The pattern repeated itself elsewhere. In the eighth-grade math test, higher-performing students scored better in 2017, but these gains were offset by lower scores from lower-performing students.

In the fourth-grade math and reading tests, lower-performing students lost ground from 2015, but not enough to affect the overall scores.

In Idaho, the achievement gap widened on the eighth-grade math test — but the pattern wasn’t nearly as pronounced on the other NAEP exams. Here’s a look at the numbers.

Idaho reported other achievement gaps. Hispanic student scores came in 19 to 25 points lower than white student scores on NAEP’s 500-point scale. Students eligible for free or reduced-price lunch scored 16 to 24 points lower than students who do not qualify for subsidized lunch. These longstanding gaps have existed since the early 2000s, according to a National Center for Education Statistics breakdown of the Idaho scores.

For more about Idaho’s NAEP scores, read our main story from Tuesday’s data drop.