As John F. Kerry barnstorms around the country, the Democratic presidential candidate rarely misses an opportunity to lambaste Republican education policies, trying to reclaim an issue that proved a vote-winner for George W. Bush in 2000.

Kerry has promised to pour an additional $200 billion into education over the next decade, to be financed by rolling back tax cuts for wealthy Americans. In the past, he has also accused the Bush administration of turning U.S. schools into "testing factories" through a "one-size-fits-all" approach that elevates test scores above real achievement.

But what may be most significant about Kerry's education proposals, many experts say, is what they have left unsaid. For all his criticism of Bush's record on education, Kerry has not called for major changes to the administration's controversial No Child Left Behind initiative.

Billed by its supporters as the most broad educational reform in more than a generation, No Child Left Behind relies on a battery of incentives and punitive measures aimed at schools to make every student in the country "proficient" in math and science by 2014. In last week's debate, Bush pointed to the law as one of his major domestic policy achievements.

Whether No Child Left Behind is achieving its goal of raising academic standards, particularly among poor minority students, has been hotly debated. Many teachers and state legislators have criticized the law as a meddlesome intrusion by the federal government in an area that has largely been left to local communities.

But rather than attack the philosophy behind No Child Left Behind, Kerry has focused his criticism on the way the law is being implemented. He has accused Bush of failing to "fully fund" the law and promised bonuses of at least $5,000 for teachers who work in the neediest schools.

"On the fundamental issues of education reform, there is more consensus between the candidates than differences," said Ross Wiener, policy director for the Education Trust, a Washington-based lobbying group that supports No Child Left Behind. "They both favor a robust federal role in setting public policy in education."

Some commentators say it is politically difficult for Kerry to attack No Child Left Behind because he voted for it in 2001, along with many other Democrats.

"No Child Left Behind is a very awkward issue for Kerry," said Chester Finn Jr., president of the Thomas B. Fordham Foundation, a conservative education think tank based in Washington. "He doesn't want education to become another flip-flop issue for him. It's much safer politically for him to talk about funding levels than to repudiate or profoundly criticize No Child Left Behind."

Over the past few months, the Bush administration has defused a grass-roots rebellion against No Child Left Behind by allowing states greater flexibility in meeting requirements for yearly progress. As a result, fewer schools are being labeled as "failing." But the new policy has also made it very difficult to compare results from year to year, undermining the law's accountability goals.

Little evidence supports the White House contention that No Child Left Behind has significantly narrowed the achievement gap between whites and minority students, said Bruce Fuller, a professor of education and public policy at the University of California at Berkeley. He cites recent test results that show a leveling out or decline in fourth-grade reading scores in 11 of the nation's 15 most populous states.

An analysis by the Education Trust, meanwhile, reported a narrowing of the achievement gap in 16 states in reading since 2002, and a widening in three. At the same time, the group reported the pace of progress was generally insufficient to reach the goal of full proficiency by 2014.

Kerry's assertion that the No Child Left Behind law is not being "fully funded" rests on the difference between the amount of money Congress authorized and the amount the administration allocated as federal subsidies to high-risk schools. This year, the shortfall was about $7 billion.

The White House says federal spending on education has risen by more than 40 percent over the past four years, with much of the extra funds being spent on the most deprived schools. A Bush education adviser, Sandy Kress, said it was "doubtful" that Congress would agree to a Kerry request for still more funding, given existing budget constraints.

In addition to extra funding for No Child Left Behind, Kerry has proposed measures to improve teaching in poor schools by paying teachers more in return for holding them more accountable. As a senator, he opposed the Republican-backed plan to establish a private-school voucher program in the District of Columbia, on the grounds that it would drain money from public schools.

Some analysts believe that the No Child Left Behind law is likely to be overhauled no matter who wins the election, because the target of 100 percent proficiency in math and science by 2014 is impossible to meet. If the law is not amended, thousands of schools across the country could eventually be closed down or reorganized.

"The leadership of both parties in Congress have put a lid on substantive changes in the law prior to the election," said David Shreve, education lobbyist for the National Conference of State Legislatures. "After the election, it's going to be difficult to keep the lid on."