As debate rages in Washington about whether a new K-12 federal education law should continue to require annual testing in math and reading, the nation’s second-largest teachers union has staked out a hybrid position.

The American Federation of Teachers, which represents teachers in most large urban school districts, wants Congress to keep annual testing — but only for informational purposes, not to determine how teachers and schools are performing.

For that purpose, the union wants to use grade span testing — where students are tested once in grades 3 to 5, 6 though 8 and once in high school.

The AFT’s position is detailed in a joint statement issued Wednesday with the Center for American Progress, a left-leaning think tank closely associated with the Obama administration.

“We propose to keep annual tests so parents have valid information about their children’s progress but want to ensure that any school accountability a system has a broader array of indicators that fully captures how our children are learning,” said CAP President Neera Tanden.

Testing has become a central issue as Congress begins work to rewrite No Child Left Behind, the 2002 federal education law that was due for reauthorization in 2007. Sen. Lamar Alexander (R-Tenn.), chair of the Senate education panel, has said he is determined to get a bipartisan bill to the Senate floor by the end of February and has scheduled the first hearing Jan. 21 on the topic of testing.

“The federal government requires 17 tests (over the course of a student’s K-12 career),” Alexander said Tuesday. “Almost every parent, almost every public school I know is asking ‘Are there too many tests?’” he said. “I want to ask the question. I want to learn from those outside the Senate: Should we keep the same tests or give states more flexibility?”

Sen. Patty Murray (D-Wash), the ranking Democrat on the Senate education panel, wants to keep annual testing, echoing a position laid out by Education Secretary Arne Duncan at the beginning of the week.

Duncan insisted that Congress maintain the annual testing requirement, saying it was an important tool to force states and schools to pay attention to historically disadvantaged students. Under Duncan, states have been persuaded to use annual test scores to make personnel decisions about teachers and identify struggling schools for intervention.

Critics say those high stakes have warped education by narrowing curricula and turning schools into test prep factories. And many states and local school districts have piled on additional tests during the school year, to track whether students are progressing sufficiently to perform well on the federally required test at year’s end. The result is a growing movement against testing, with thousands of parents across the country trying to “opt-out” their children from standardized tests, and some school districts trying to do the same.

The National Education Association, the country’s largest teachers union, supports grade span testing.

But the AFT said there is value in annual testing, as long as it is used for diagnostic purposes.

“More data doesn’t necessarily mean better data, and it doesn’t ensure that data is being used to actually help improve learning,” AFT President Randi Weingarten said. “Annual tests, if they are reliable and diagnostic, provide important information for students, parents, teachers and schools. In my experience, struggling schools want to do the right thing and improve, but they need supports not sanctions. In focusing on grade-span testing for accountability purposes, similar to what happens now in high school, we can make sure that these schools are doing what they need to do. But even these grade-span tests would be one component of a robust system of multiple measures.”