Testing season begins soon in U.S. public schools, requiring millions of students to spend days answering standardized questions in math and reading, as mandated by an outdated federal law.

But this year is filled with tumult. Educators are questioning the purpose of testing, lawmakers in several states are pushing back against federal regulations, and a momentous standoff between California — the state with the largest number of public school students — and the Obama administration looms.

California is defying the requirements of No Child Left Behind, the federal education law that was set to expire in 2007 but hasn’t been replaced by Congress. The law says every state must give annual tests in math and reading to every student in grades 3 through 8 and report those scores publicly.

But California says it can’t administer the tests this year because, like much of the country, it has adopted new Common Core national academic standards and the corresponding exams aren’t ready.

Nearly everyone agrees that No Child Left Behind is broken, and the Obama administration has excused most states from various aspects of that law. But for Education Secretary Arne Duncan, watering down the law’s testing requirement is a bridge too far. He has threatened to withhold at least $3.5 billion in annual federal funding — money that California uses to educate poor and disabled children — if the state does not satisfy federal concerns.

“Testing is a critical component of accountability,” said Deborah Delisle, assistant secretary for elementary and secondary education at the Education Department. “Parents and community members want to know how we can measure student growth and student learning. We hold central to the fact that testing is an essential component.”

California is grappling with a problem facing much of the country this year. Forty-five states and the District of Columbia are teaching math and reading differently as a result of new academic standards. Known as the Common Core, the K-12 standards require new curricula, materials and teaching approaches.

But the accompanying standardized tests won’t be ready until next year.

That leaves states in a bind, as federal law requires that they test students and report the scores annually. Without new exams, most states plan to dust off their old tests, make some changes and hope for the best.

“That’s like teaching kids about Greece and Rome and then testing them on ancient Egypt,” said Eric G. Luedtke, a Montgomery County teacher and state lawmaker who is trying to stop Maryland from administering its old tests.

Teachers and administrators are particularly alarmed because student test scores on standardized tests are increasingly used to make decisions that reward or punish schools and educators.

Recognizing that states will be giving tests that are out of sync with instruction, federal officials are permitting them to suspend accountability decisions based on this spring’s test scores. In the District and 36 states, some students will be field-testing questions for the new Common Core exams, and the federal government is excusing those students in some states from also having to take the old state tests.

But the Obama administration will not back down from the requirement that every state test every student in certain grades, even if that means giving old tests that don’t match the current curriculum.

Maryland lawmakers say the federal government should not force the state to administer an outdated exam.

“Put yourself in the place of one of my students,” Luedtke, a Democratic member of the state House of Delegates, said during testimony last week about his bill to stop the state from giving the MarylandSchool Assessment.

“You’re 11 years old,” he said. “You come to school, and you want to do well. You want to prove to your teachers that you’re smart and you pay attention and you’re working hard. You come to class one day, and they put a test in front of you, and you open the first page, read the first question, and you have no idea what they’re asking you to do. All you know is that you’re failing, and you feel stupid, and you feel all the work you’ve put in is for naught.”

The state will waste days of class time and about $7 million to give a useless test to 360,000 students, he said.

Jack Smith, Maryland’s chief academic officer, told lawmakers that Maryland teachers can still glean information from the old tests. “There is some value,” he said, adding that results can help teachers identify student weaknesses.

But on the whole, there is little overlap between old state tests and new Common Core material, said Andrew Porter, dean of the education school at the University of Pennsylvania, who has studied the issue.

In California, legislators overwhelmingly passed a law to retire the old tests.

“Holding students accountable for old exams that don’t measure where you want to go, there’s a disconnect there,” said Deborah Sigman, a deputy superintendent with the California Department of Education. “Those old tests don’t send the right message.”

States that are giving old tests make it difficult for teachers to fully implement the Common Core, said Daniel Koretz, an assessment expert at the Harvard Graduate School of Education. “The really serious harm may have already been done,” he said. “Teachers have been getting an inconsistent message about what they’re supposed to be doing.”

In place of the old tests, California intends to give field tests, with sample questions, of the new Common Core exam. Because a field test is not designed to be a reliable measure of student achievement, California will not score the tests, and the results will not be publicly reported, as required by federal law. The state intends to use last year’s test scores to make decisions about school performance, essentially maintaining the status quo for this transition year, Sigman said.

The argument over what kind of test to administer coincides with a raging national dispute over the Common Core standards themselves.

Supporters say the Common Core standards emphasize critical thinking and analytical skills, as opposed to rote learning, and will enable U.S. students to better compete in the global marketplace.

The opponents include tea party activists who say the new standards amount to a federal takeover of local education and progressives who bristle at the emphasis on testing and the role of the Gates Foundation, which has funded the development and promotion of the standards. Some academics say the math and reading standards are too weak; others say they are too demanding, particularly for young students.

Meanwhile, educators across the country are watching California’s standoff with Washington.

California officials say that beginning March 18, they will give the math and reading Common Core field tests to all 3.4 million students in the designated testing grades, at a cost of about $51 million.

The federal government has not resolved what to do about California, but federal officials said a decision could come as soon as this week.