THE TROUBLING condition of America's public high schools has long been recognized. Even so, it was sobering to learn last week that high school seniors, though taking more advanced classes and getting better grades, are performing dismally on national tests.

The data from the U.S. Education Department revealed a disturbing incongruity between how well schools say students are doing and how well students really are doing. Transcripts show more students taking supposedly more rigorous courses, yet raising their grade-point average from 2.68 in 1990 to 2.98 in 2005. But when these same students had to demonstrate what they learned on nationally recognized tests, only 35 percent scored proficient or better in reading. That's the worst performance since the testing began in 1992.

Why? Advanced classes may have highfalutin course descriptions, but the curriculum has been dumbed down. Pressure to pass students has caused grade inflation. The students hurt most are poor and minority. The Post's Amit R. Paley vividly demonstrated this by visiting two classes supposedly teaching the same material. Students at a more affluent high school faced higher expectations and standards than those at a school with more poor and black students. But even students who typically are seen as doing well in school -- suburban, middle-class children -- showed no gains. And the data don't deal at all with the many children who drop out before 12th grade.

Some states are moving to overhaul high schools and stiffen standards. Twenty-nine states, including Maryland and Virginia, are working with Achieve, a nonprofit group, to raise academic standards and accountability so students graduating from high school are able to meet the demands of college or work. So far, the No Child Left Behind Act has focused mainly on the elementary grades. The national debate over the law's reauthorization must include a robust discussion of how to improve high schools and create national standards. If not, any progress made in boosting achievement in elementary grades will be lost.