The presumptive Democratic presidential nominee spoke by video link from Butte, Mont., where he spent the Fourth of July. The response to his speech was generally enthusiastic from a union that has already endorsed him, USA Today reported.

"I'm tired of hearing teachers blamed for our problems," Obama said. "I want to lead a new era of mutual responsibility in education."

But the NEA delegates were less enthusiastic when Obama listed problems such as the high U.S. dropout rate, poor scores in math and science, and the millions of students reading below grade level. Some delegates booed when Obama said teachers should get additional pay for teaching in tough schools, mentoring students or acquiring additional skills.

"In some places we've already seen that it's possible to find new ways to increase teacher pay that are developed with teachers, not imposed on teachers," he said, to more boos.