Catching up to the reality already faced by many of its members, the nation’s largest teachers’ union on Monday affirmed for the first time that evidence of student learning must be considered in the evaluations of school teachers around the country.

In passing the new policy at its assembly here, the 3.2 million-member union, the National Education Association, hopes to take a leadership role in the growing national movement to hold teachers accountable for what students learn — an effort from which it has so far conspicuously stood apart.

But blunting the policy’s potential impact, the union also made clear that it continued to oppose the use of existing standardized test scores to judge teachers, a core part of the federally backed teacher evaluation overhauls already under way in at least 15 states.

Today’s New York Times.