By NICHOLAS D. KRISTOF – The New York Times.

The Democratic Party has battled for universal health care this year, and over the decades it has admirably led the fight against poverty — except in the one way that would have the greatest impact.

Good schools constitute a far more potent weapon against poverty than welfare, food stamps or housing subsidies. Yet, cowed by teachers’ unions, Democrats have too often resisted reform and stood by as generations of disadvantaged children have been cemented into an underclass by third-rate schools.

President Obama and his education secretary, Arne Duncan, are trying to change that — and one test for the Democrats will be whether they embrace administration reforms that teachers’ unions are already sniping at.

It’s difficult to improve failing schools when you can’t create alternatives such as charter schools and can’t remove inept or abusive teachers. In New York City, for example, unions ordinarily prevent teachers from being dismissed for incompetence — so the schools must pay failed teachers their full salaries to sit year after year doing nothing in centers called “rubber rooms.”

A devastating article in The New Yorker by Steven Brill examined how New York City tried to dismiss a fifth-grade teacher for failing to correct student work, follow the curriculum, manage the class or even fill out report cards. The teacher claimed that she was being punished for union activity, but an independent observer approved by the union confirmed the allegations and declared the teacher incompetent. The school system’s lawyer put it best: “These children were abused in stealth.”

The effort to remove the teacher is expected to cost about $400,000, and the outcome is uncertain. In New York City, with its 80,000 teachers, arbiters have removed only two for incompetence alone in the last couple of years. We tolerate failed teachers — and failed arbiters — as long as it’s not our own kids who suffer.

In another case cited by Mr. Brill, the union hailed its defense of a high-school teacher — who had passed out in front of her class, allegedly smelling of alcohol, with even the principal unable to rouse her. The union fought to secure her return to teaching, Mr. Brill wrote, until she passed out again, and her “water bottle” turned out to contain alcohol.

In California, we see the same pathology — as long as the students in question are impoverished and marginalized, with uncomplaining parents, they are allowed to endure the kind of teachers and schools that we would never tolerate for our own kids.

A Los Angeles Times article this year recounted how a teacher rebuked an eighth grader who had been hospitalized for slashing his wrists in a suicide attempt. “Carve deeper next time,” the teacher allegedly advised. He was even said to have added: “You can’t even kill yourself.” A review board blocked the termination of that teacher.

The Los Angeles Times investigation found that it is so expensive to remove teachers that the authorities typically try to do so only in cases of extreme misconduct — not for something as “minor” as incompetence.

Of course, there are many other obstacles to learning: lack of safety, alcohol and narcotics and troubled homes and uninterested parents. But there’s mounting evidence that even in such failing schools, the individual teacher makes a vast difference.

Research has underscored that what matters most in education — more than class size or spending or anything — is access to good teachers. A study found that if black students had four straight years of teachers from the top 25 percent of most effective teachers, the black-white testing gap would vanish in four years.

There are no silver bullets, but researchers are gaining a better sense of what works in education for disadvantaged children: intensive preschool, charter schools with long hours, fewer certification requirements that limit entry to the teaching profession, higher compensation to attract and retain good teachers, objective measurement to see who is effective, more flexibility in removing those who are ineffective.

Unions are wary in part because school administrators can be arbitrary and unfair. Yet there are some signs that the unions are rethinking their positions in very welcome ways. The National Education Association has announced an initiative to improve teaching in high-poverty high schools, and the American Federation of Teachers is experimenting with teacher evaluation that includes student performance data.

Neither initiative reflects sufficient urgency. But let’s hope this is a new beginning. I’m hoping the unions will come round and cooperate with evidence-based reforms, using their political clout to push to raise teachers’ salaries rather than to protect ineffective teachers.

This is the central front in the war on poverty, the civil rights issue of our time. Half a century after Brown v. Board of Education, isn’t it time to end our “separate but equal” school systems?