Some experts said that in response to declining achievement, policymakers should look to a few states that have shown recent improvements in NAEP test scores for younger children. State-by-state results are not available for the 12th-grade level.

“There’s a road map out there from states like Louisiana and Tennessee, focused on high-dosage tutoring, high-quality curriculum and clear information for parents on where their kids stand,” said Marc Porter Magee, chief executive of 50CAN, an education advocacy group. “What’s missing now is the political will to bring it to every state.”