The unions have experienced a burst of energy and public support over the past two years, as teachers in a string of states and cities mounted walkouts in favor of higher pay and more school funding, and against competition from charters.

Teachers in Chicago, the nation’s third-largest school district, are now on strike, and Ms. Warren has offered her support. She has proposed policies that would make it easier for unions to organize teachers and other workers, and easier for employees to strike.

On teacher pay, Ms. Warren’s plan promises new federal funding but does not offer as much detail as a proposal by Senator Kamala Harris of California, which supports an average teacher raise of $13,500 per year, with more money for teachers in low-income schools.

“We have to get a little edgier than just, ‘Pay teachers more,’” said Paul Reville, a professor at the Harvard Graduate School of Education and a former Massachusetts secretary of education. He suggested that in addition to a broad anti-poverty agenda, candidates should support a longer school day and year, with afternoon and summer enrichment activities that could help children from low-income families keep up with more affluent peers.

“We have millions of children who are being grossly underprepared for the 21st-century labor market, to say nothing of citizenship in a complex democracy,” he said.

Ms. Warren has steadily gained momentum in the Democratic primary contest, and she now stands as a front-runner alongside Mr. Biden. Last week’s debate, in which she was the target of a barrage of attacks from other candidates, was indicative of her perceived strength in the race.

On the campaign trail, Ms. Warren often tells crowds that she had dreamed of becoming a public-school teacher ever since the second grade, recounting how she lost her job after her first year as a special needs teacher because she became pregnant. She has said she would appoint a former public-school teacher as education secretary and, six months ago, Ms. Warren released a higher education plan that calls for canceling student loan debt and eliminating tuition at public colleges. She has also proposed expanding access to free preschool and capping child care expenses at 7 percent of parents’ income, with free child care for low-income families.