Democratic candidates for president didn't miss their chance to address over 7,000 members of the National Education Association, which will be a powerful player in the Democratic primary process. Hillary Clinton, Martin O'Malley and Bernie Sanders all sent video messages to the teachers, who were gathered at the NEA's Representative Assembly.

In her address, Clinton used a theme of teachers unlocking potential in students. She talked about how teachers had encouraged her and her mother at a young age. "Every semester, in schools across the country, you multiply my mother's story by millions," Clinton told the teachers. "When we invest in our children, we do invest in our country's future, and we need to do more of that." Clinton promised high quality preschool, a doubling of spending on the federal Head Start program, and making college affordable for every single person.

Sanders struck a more ideological tone. "We need some fundamental changes in our national priorities," Sanders said. "Instead of giving tax breaks to billionaires, maybe we invest in our children, maybe we invest in education." He promised to make progress on fixing No Child Left Behind, on universal pre-K and on free college tuition. He also called teachers the real heroes and heroines of the country.

O'Malley tried to strike an optimistic note. "I believe, like you, that America's best days can still be in front of us," O'Malley said. He didn't make any specific promises about what he would do as president, but O'Malley touted the pro-union reforms he implemented in Maryland while serving as governor. For example, spending more on public education and making college more affordable. "This is what we do as Americans, to do more in every generation, to give our children a future with more opportunity, rather than less."

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