Hillary Clinton takes the stage at Dartmouth College in Hanover, N.H., Tuesday. (Brian Snyder/Reuters)

HILLARY CLINTON has had a decades-long interest in education in which she has not shied from disagreeing with the teachers unions that are a core constituency of the Democratic Party. So when her presidential candidacy won unexpectedly early endorsements from the two major education unions, the question arose of whether she would stand her ground. If her recent comments on charter schools are any indication, the answer is: not so much.

At a town hall meeting this month in South Carolina, Ms. Clinton criticized charter schools, saying that “most” intentionally exclude or expel children who are difficult to educate and blurring over the fact that charters, like their traditional counterparts, are public schools. Her rebuke that these schools “don’t take the hardest-to-teach kids, or, if they do, they don’t keep them” was a marked change from her previous championing of public charter schools, including as first lady of Arkansas and of the country.

The quality of charter schools, like that of traditional schools, varies, and undoubtedly some fit her description. But her industry-wide indictment of the charter movement simply doesn’t square with the facts. Most charters have more applicants than desks and by law must select students by lottery. Moreover, studies show charter schools serve higher percentages of low-income, black and Latino students — all subgroups that have lagged behind their more advantaged peers — than traditional public schools. Research also shows that charter schools produce greater student learning gains than traditional public schools, particularly for poor and minority students.

The one academically challenged group underserved by charters are students with disabilities, but, as a recent report from Bellwether Education Partners noted, there are factors other than charter unwillingness that are at play, such as school size, available resources and transportation barriers. Charter advocates acknowledge the need for improvement in welcoming children with special needs and are working to bring that about.

Candidates distancing themselves from previous positions for political advantage is a sad fact of life of political campaigns, and Ms. Clinton’s backpedaling on charters is in keeping with her posturing on other issues to stave off a progressive challenge in the Democratic primary from Sen. Bernie Sanders (I-Vt.). What is pernicious about this particular cave is that in satisfying the unions, she sells out an even more important constituency: the poor and minority children who look to charters to get the education they need and deserve.