When the District’s newly constructed Dunbar High opens next month, Principal Stephen Jackson will use the same hard-line student segregation policy that worked for him at the old school building. Ninth-graders can mix only with ninth-graders. They will eat together and attend class on their own floor. Same for 10th-graders. Only juniors and seniors can fraternize together.

Stricter still are the prohibitions on ninth-graders who failed to make it into the 10th grade last year. They will report to a remedial school within Dunbar known as a “twilight academy.” Classes begin at 3:30 p.m., after regular school has let out, and last until 7:30 p.m.

“What we did was separate students according to age and need,” Jackson said. “This helps us to better monitor their progress, both academically and socially. As for the repeaters, you just can’t put 17- and 18-year-olds who have failed ninth-grade math or English in a class with 13- and 14-year-old children. It just doesn’t work.”

That part is a no-brainer, for sure. But Jackson’s entire approach appears to be paying off. In the two years since he began cordoning off his youngest students and establishing a separate school for older underachievers, suspensions at Dunbar have been reduced by 80 percent — the steepest decline of any public high school in the city. Last year, truancy fell by 11 percent.

With repeaters no longer crowded into classrooms with newcomers, he says, 97 percent of first-time ninth-graders were promoted to the 10th grade this past school year. Perhaps most encouraging, students enrolled in the academy are making up lost ground faster than anyone had predicted.

“We have been able to get some students back on track within a short time,” Jackson said. “Some take longer, depending on how serious they are about education when we get them. What we do is nag and nurture. We visit the homes when students are absent. . . . We talk to parents and put lots of resources into saving those kids.”

Little wonder that, come fall, D.C. Schools Chancellor Kaya Henderson plans to put similar “twilight academies” into nine other high schools. But Jackson’s success also raises serious questions about why such an approach would even be needed.

The problem apparently stems from what school officials call a “ninth-grade bulge,” a blockage in the educational pipeline caused by an extraordinary number of ninth-grade failures. The problem plagues urban school systems throughout the country. In the District, only six out of 10 first-time ninth-graders are promoted to 10th grade.

As it turns out, many of them are barely able to read on a third-grade level, making them functionally illiterate. How did they make it to high school in the first place?

“Unfortunately, those students were allowed to fall through the cracks,” Jackson said. “Someone did not intervene early enough. However, when we get the kids, we do not turn them away. We have to find ways to give them as much knowledge and information as we can. It’s difficult, but you have to start somewhere.”

It should go without saying, however, that high school is not that place. But Jackson’s achievements may lead some to believe that it is. What’s the rush if a high school student can make up for learning deficits that began in elementary school?

The truth is: Very few can.

That’s why Jackson’s approach needs to be adopted much earlier. And because he and his staff see their work as a commitment, if not a calling, not just any old principal will do.

Among the most critical qualifications for a school leader is a realistic view of the devastating effects that poverty can have on a child’s ability to learn. I thought that the rise in poverty caused by the recession would show that it was wrong to generalize about poor people. I was wrong. Too many people still assume that poverty is the result of ignorance and laziness. The myth persists that anyone can get rich in America if only they are smart and work hard.

“Many parents are having to work around the clock just to survive and are simply unable to stay as involved with their children’s education as they would like,” Jackson said. “Some students have fallen behind because their parents became ill or died. The responsibility of raising the siblings fell on them. And there are other reasons that we will never know.”

Supposed we accepted that reality and chose to intervene in the lives of those children much earlier? Suppose there were principals like Jackson in every school — as well as volunteers, tutors, mentors, people who pitched in to help instead of just throwing stones?

It’s our choice. Twilight academies could represent the sunrise of education reform in the city — or a descent into the twilight zone.

To read previous columns, go to washingtonpost.com/milloy.