Wading in to the growing backlash against the Common Core standards today, American Federation of Teachers President Randi Weingarten called for a moratorium on using scores tied to the new standards to make important decisions.

Weingarten made the proposal in a speech before business and civic leaders at the Association for a Better New York, days after students across the state completed tests aligned to the Common Core for the first time and months after local union leaders began sounding the alarm about the state’s Common Core rollout.

She praised the learning standards and said she did not oppose testing students on them. But she said a “failure of leadership” and a “broken accountability system” could derail the Common Core’s chances of boosting student achievement in New York and beyond.

States and districts frequently use test scores to decide which schools to close and students to retain. Increasingly, they are also using test scores to measure teachers’ performance, a policy shift that Weingarten has supported but many of her members have not. Waiting at least a year before acting on the scores of Common Core-aligned tests would give students and teachers the chance to adjust to the higher standards and let states and districts assess whether the tests are yielding meaningful results, Weingarten said.

“That’s what assessment and accountability are supposed to be,” she said. “You see if the whole shebang works, before you say it’s ready for prime time.”

The moratorium proposal netted the national union leader swift criticism for impeding the nation’s first successful push to get multiple states to set shared expectations about student learning. Forty-six states and the District of Columbia adopted the standards, meant to allow comparisons of students across states, although only Kentucky and New York have administered tests tied to them so far.

“Every reform effort through history has had people, special interests, saying let’s slow down, let’s put the breaks on this, we’re not ready,” said city Department of Education spokesman Andrew Kirtzman, who attended the speech. “It can’t happen. The Common Core is the future and it has to move forward.”

StudentsFirstNY, the state branch of a national education advocacy organization headed by Michelle Rhee that often opposes policies that teachers unions support, said Weingarten was attempting to “derail teacher evaluations” and was part of the “education status quo” that calls for “endless delay.”

Weingarten’s proposal was aimed at a national audience, and she exhorted parents, teachers, and students to write letters to their state education commissioners to advocate against attaching stakes to Common Core test scores. Legislation is on the table in several states to roll back the Common Core, which some on the right say comes dangerously close to a federal intrusion into local education decisions.

But she also focused heavily on New York City and state, where union leaders have complained bitterly about the lack of Common Core-aligned curriculum materials available to teachers. Weingarten cited NEST+m, a highly selective school for gifted students on the Lower East Side, as an “the exception, not the rule” because teachers were able to spend dozens of hours rejiggering their lesson plans to reflect the new standards’ emphases on critical thinking and informational texts.

She also alluded to local protests against “field testing,” or the practice of administering test questions that do not count to assess their quality. Weingarten said she agreed with the state that field testing is essential to developing high-quality tests.

Yet for New York City students, Weingarten’s moratorium would not require many changes. State education officials have said they will not label additional schools as low-performing based on this year’s scores. In the city, which has used test scores to decide which schools to close, a lame-duck mayoral administration won’t be able to close any schools at all. The city has also set aside the use of state test scores to decide which students should be held back. And because the city has not reached a teacher evaluation deal with its local union, test scores won’t factor into teachers’ annual ratings.

Most other districts across the state do have teacher evaluation systems in effect that weigh student test scores, an arrangement that has caused anxiety as state officials have warned that scores are likely to plummet this year. But the ratings will look at how teachers’ students do as compared to other teachers’ students, not compared to past scores. And in a statement released today in response to Weingarten’s speech, State Education Commissioner John King said, “We have asked districts to be thoughtful in their use of the data from this first year of Common Core assessments when evaluating teacher performance and we have every confidence that they will be.”

Yet even state education policy makers are divided about whether the state has been as cautious as it should have been in rolling out the new standards. After the speech today, Harry Phillips, a member of the state Board of Regents, approached Regents Chancellor Merryl Tisch with a question.

“Don’t you think the commissioner should say it shouldn’t be high stakes until we get the curriculum in?” Phillips asked. The state is creating free reading and math curriculum materials that are tied to the Common Core, but they won’t be complete until the end of the year.

Tisch replied, “I think we’ve always been silent on how districts use the test.”

Speaking to reporters, Tisch repeated a defense of the standards that she has made over and over in recent weeks, as parents and teachers expressed increasing anxiety about the impact of the new tests.

“When we continue to educate to a lower standard…we are saying that New York State can not, will not be competitive in a 21st century economy,” she said. “I say the day for a low standard is over and let’s figure out a way to embrace a new challenging standard.”