WASHINGTON — For nearly six years, the federal government has defined school success mainly by how many students pass state reading and math tests. But a growing number of educators and lawmakers are pushing to give more weight to graduation rates, achievement in science and history and even physical education.

The debate over the formula for rating the nation's public schools has stalled efforts in Congress to revise the No Child Left Behind law. At issue: What's the best way to measure whether schools are doing their job?

Unlike questions on the state math and reading tests taken by millions of children, this one has no clear answer. Reaching consensus in the coming election year is expected to be difficult. Without congressional action, the 2002 law will stay as it is.

"Lots of stakeholders have different answers to this question," said Michael Casserly, executive director of the Council of the Great City Schools, a D.C.-based coalition of urban school systems. "The tug of war is over, if not state assessments, then what?"

The American Society of Civil Engineers wants science tests added to the mix. The NAACP and other groups say schools should get credit for achievement in subjects other than reading and math, as well as for improvement in graduation and college admission rates.

But the Bush administration and some civil rights, education and business groups say that too many tweaks would weaken a law credited with revealing pockets of struggling students, especially among poor children, minorities and those with disabilities. In their view, a complex rating system would mask problems in schools with many students who haven't mastered basic reading and math, skills they call the building blocks to success.

The law requires annual reading and math tests in third through eighth grades and once in high school. Schools and subsets of students — including ethnic minorities and students from poor families — must make gains over time. High schools also must reach target graduation rates, but the state goals have been criticized as weak and inconsistent.

Tom Loveless, director of the Brown Center on Education Policy at the Brookings Institution, said the challenge is creating a rating system that includes a range of measures and provides a clear picture of a school's effectiveness.

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