A decade ago, the No Child Left Behind Act ushered in an era of school reform relentlessly focused on closing race- and income-based "achievement gaps" in test scores and graduation rates. For all the subsequent critiques of NCLB, this has been universally hailed as an unmitigated good. It is not. It has shortchanged some children, undercut excellence and undermined support for reform.

A year ago, Berkeley High School in Berkeley, Calif., moved to eliminate five science teachers and after-school science labs for Advanced Placement classes so as to devote those resources to struggling students. In Sacramento, Calif., low-performing students are only permitted to enroll in math, reading and gym, in a mad dash to close the achievement gap.

"We should not renounce laudable efforts to do right by disadvantaged kids." -- Frederick Hess

Focusing on the neediest students is admirable, as far as it goes. The real problem has been the unwillingness of gap-closers to acknowledge the costs. Instead, many reformers have sought to stifle those who dare even to suggest there are negative consequences to gap-closing — branding such sentiments ill-informed or even racist.

Today, the result is that proficient students are receiving little attention in our nation's classrooms. In 2008, a survey of the nation's teachers found that 60 percent said struggling students were a "top priority" at their schools, while just 23 percent said the same of "academically advanced" students. Eighty percent said struggling students were most likely to get one-on-one attention from teachers; just 5 percent said the same of advanced students.

RAND Corporation scholars have previously determined that low-achieving students benefit when placed in mixed-ability classrooms (faring about five percentage points better than those placed in lower-track classes) but that high achievers fare six percentage points worse in such general classes.

Thus, our would-be reformers have left advanced students to fend for themselves. The Brookings Institution's Tom Loveless has reported that, while the nation's lowest-achieving students made significant gains in reading and math between 2000 and 2007, the progress by top students was "anemic."

An exclusive focus on low-achieving students ignores the fact that students have different needs. Children from more educated families tend to start school with much larger vocabularies, more exposure to the written word, more time having been read to and more of the habits that make for a responsible, successful student. The instruction and support that can help disadvantaged students acquire the skills and knowledge they need may be inappropriate for children ready for new challenges.

And it's not as if we can afford to coast. Just 6 percent of U.S. eighth-graders scored "advanced" on the 2007 international math and science test, while more than a dozen nations fared at least twice as well. The University of Arkansas' Jay Greene has reported that even high-performing U.S. school systems are only middling when compared to international norms.

Achievement gap mania has also undermined support for school improvement. It has signaled to the vast majority of American parents that school reform isn't about their kids. Consider that, in the most recent annual Gallup poll on attitudes toward schooling, just 20 percent of respondents deemed "improving the nation's lowest-performing schools" the most important education challenge. Progressive blogger Matt Yglesias has observed that we would get more real improvement if parents and voters were less "morbidly obsessed with semi-mythical tales of a 'broken' school system that they're fortunate not to be stuck in."

Solutions designed with an eye to gap-closing can be unhelpful when it comes to serving other students and families. For instance, reforms that encourage the best teachers to migrate to schools and classrooms serving low-achieving children offer nothing but loss to most middle-class families.

What to do? We should not renounce laudable efforts to do right by disadvantaged kids. But we must admit a hard truth: Different kids have different needs, and content or instruction which makes sense for at-risk students may ill serve their more proficient peers.

We must also approach school choice as part of a broader continuum of offering "educational choices." This means taking seriously the concerns and needs of the 75 percent of families that may not want to change schools but would welcome better options when it comes to world languages, reading or math instruction for their kids.

And we have to abandon redistributive policies that rob Peter to pay Paul — moving good teachers into struggling schools, for example, instead of focusing on hiring and keeping better teachers. Today, for instance, while Teach For America is recruiting mission-driven college graduates into our neediest communities, there's an easy opportunity to grow the pool of good teachers by aggressively pursuing talented candidates for less demanding conditions. Yet no similar venture is even attempting this.

We can do much better by all our children, but the first step is escaping the false assurances and pinched thinking of the achievement gap era.

Frederick M. Hess is director of education policy studies at AEI.