The union’s new dual role as defender of union protections and promoter of reform created some unlikely tableaus. At one point an angel-voiced folk singer with a guitar took to the stage to lead the thousands of teachers in a sing-along called “Solidarity Forever.” At another point, the narrator of a video projected on the hall’s multiple Jumbotrons began his report about inspiring teachers with the following sentence: “We have a huge problem of teacher quality in this country.”

“They’re just shifting back and forth,” said Jana Wells, 53, a teacher from Glendale, Calif., who called herself one of the few Republicans representing the California caucus. “And on the endorsement of Obama, it’s scare tactics — it’s like if we don’t do this right now, our enemies will win.”

The debate over the new teacher evaluation policy largely focused on the concern that by even mentioning test scores, the union would further open the door to their use. Some teachers also balked at another section of the policy — the proposal that failing teachers be given only one year to improve, instead of the standard two. But in the end a clear majority voted yes.

Segun Eubanks, the director of teacher quality for the union, said the new policy was intended to guide, not bind, state and local union chapters. It tries to close the disconnect between the many local union chapters that have already assented to using student test scores in teacher evaluations, and the union’s national policy that explicitly opposed their use. Now the union can offer those chapters support, and conduct research on the impact of standardized tests.

“What it says is, now we are willing to get into that arena,” Mr. Van Roekel said. “Before, we weren’t.”

The policy calls for teacher practice, teacher collaboration within schools and student learning to be used in teacher evaluations. But for tests, only those shown to be “developmentally appropriate, scientifically valid and reliable for the purpose of measuring both student learning and a teacher’s performance” should be used, the policy states, a bar that essentially excludes all existing tests, said Douglas N. Harris of the University of Wisconsin, a testing expert.

Mr. Eubanks said, “We believe that there are no tests ready to do that,” though he added that with the new national Common Core curriculum standards being rolled out, new tests might be created that could meet the bar.