Education Secretary Arne Duncan speaks about the administration's priorities for education on Jan. 15 at a D.C. elementary school. (Jacquelyn Martin/AP)

Education Secretary Arne Duncan gives Congress a 50-50 chance of reaching a deal to rewrite No Child Left Behind, the federal education law that expired in 2002.

“We would love to find a way to fix it. We think obviously much of it is outdated,” Duncan said Wednesday, speaking at the winter meeting of the U.S. Conference of Mayors in Washington. “The only way we’re going to fix it is if folks in Washington work in a bipartisan way. There’s a chance that will happen, but it’s not a guarantee.”

Duncan made his remarks on the same day that the Senate kicked off its most serious effort yet to rewrite the law with a hearing focused on its standardized testing requirements.

There is plenty for Congress to disagree upon in No Child Left Behind, which is hundreds of pages long and directs billions of dollars in federal spending. But standardized testing has generated the most attention and pushback across the country and on Capitol Hill.

Duncan, backed by influential civil rights groups, wants to continue administering annual standardized tests to students in grades three through eight, and once in high school, to hold schools accountable for the achievement of all students, including poor and minority children.

“I don’t think we ever should walk away from assessing our students on an annual basis,” he told the mayors on Wednesday.

But parents and teachers have argued that too many schools have become test prep institutions, while many in the new Republican-dominated Congress say the annual testing requirement amounts to a federal overreach.

“Are there too many tests? Are they the right tests? Are the stakes for failing them too high? What should Washington, D.C., have to do with all this?” Sen. Lamar Alexander (R-Tenn.), chair of the Senate education committee, told the Associated Press before Wednesday’s hearing.

President Obama did not address No Child Left Behind nor annual testing in his State of the Union address Tuesday night. Duncan said Wednesday that he has Obama’s support.

“We both think the same thing,” Duncan said. “We think in some places there’s too much, and too much is too much, whether it’s testing or test prep or teaching to the test. Where it’s redundant and duplicative and not helpful, we want to challenge that. We also believe we ought to know whether students are learning or not — and to know every year whether students are learning or not.”