This is quite a remarkable story. Samuel Freedman wrote in the New York Times in 2008 about a social studies teacher in Alliance, Nebraska. He wrote about a world geography class in 1993 where students learned about genocide. Their teacher was Tim Walz.

After studying the circumstances that set the climate for horrific mass murder, Mr. Walz gave a final exam in which the students identified a country where genocide might happen. They picked Rwanda. Mr. Walz was a good teacher.

The story in 2008 begins:

In 1993, when Travis Hofmann was a freshman of 15, he had traveled little beyond the sand hills that surrounded his hometown, Alliance, Neb. He was the son of a railroad engineer, a trumpeter in the high school band, with a part-time job changing the marquee and running the projector at the local movie theater. 

In Travis’s class in global geography at Alliance High School, however, the teacher introduced the outside world with the word and concept of genocide. The teacher, Tim Walz, was determined that even in this isolated place, perhaps especially in this isolated place, this county seat of 9,000 that was hours away from any city in any direction, the students should learn how and why a society can descend into mass murder.

Mr. Walz had already taught for a year in China, and he brought the world into his classroom in the form of African thumb pianos and Tibetan singing bowls. For the global geography class, he devised something far more ambitious than what the curriculum easily could have been — the identification and memorization of capitals, mountain ranges and major rivers. It was more ambitious, too, than a unit solely on the Holocaust of the sort many states have required.

“The Holocaust is taught too often purely as a historical event, an anomaly, a moment in time,” Mr. Walz said in a recent interview, recalling his approach. “Students understood what had happened and that it was terrible and that the people who did this were monsters.

“The problem is,” he continued, “that relieves us of responsibility. Obviously, the mastermind was sociopathic, but on the scale for it to happen, there had to be a lot of people in the country who chose to go down that path. You have to make the intellectual leap to figure out the reasons why.”

So Mr. Walz took his students — Brandon Bell, the wrestler; Beth Taylor, the cheerleader; Lanae Merwin, the quiet girl always reading some book about Queen Elizabeth; and all the other children of mechanics, secretaries and a town dentist — and assigned them to study the conditions associated with mass murder. What factors, he asked them to determine, had been present when Germans slaughtered Jews, Turks murdered Armenians, the Khmer Rouge ravaged their Cambodian countrymen?

“It was different and unusual, certainly not a project you’d be expecting,” Mr. Hofmann, now 31, of Phoenix, remembered recently of the class. “The biggest part was just the freedom to explore things. No matter how abnormal or far-fetched an idea might sound, you can form an opinion. Instead of just going in and having a teacher say, ‘Here’s information, learn it, know it, you’ll be tested on it,’ it was, ‘Here’s an idea, run with it.’ ”

For nine weeks through the winter and early spring that school year, through the howling blizzards and the planting of the first alfalfa on the plains, the class pored over data about economics, natural resources and ethnic composition. They read about civil war, colonialism and totalitarian ideology. They worked with reference books and scholarly reports, long before conducting research took place instantly online. 

Most, like Mr. Hofmann, had spent their entire lives in and near Alliance. A few had traveled to Washington, D.C., with the school marching band. A few had driven four hours to Denver to buy the new Nirvana CD. Mostly, though, the outside world was a place they built, under Mr. Walz’s tutelage, in their own brains. 

When the students finished with the past, Mr. Walz gave a final exam of sorts. He listed about a dozen current nations — Yugoslavia, Congo, some former Soviet republics among them — and asked the class as a whole to decide which was at the greatest risk of sliding into genocide.

Their answer was: Rwanda. The evidence was the ethnic divide between Hutus and Tutsis, the favoritism toward Tutsis shown by the Belgian colonial regime, and the previous outbreaks of tribal violence. Mr. Walz awarded high marks.

Then summer arrived and school let out. The students did what teenagers did in Alliance over the summer. They water-skied at the reservoir, swam in the Bridgeport sand pits and mostly “cruised the Butte,” endlessly driving up and down Box Butte Avenue.

THE next April, in 1994, Mr. Walz heard news reports of a plane carrying the Rwandan president, Juvenal Habyarimana, being shot down. He told himself at the time, “This is not going to end up good.”

It did not. Over the next three months, militant Hutus killed 800,000 Tutsis and moderate Hutus. The reports reached even The Alliance Times-Herald, the local daily newspaper. Mr. Walz’s students, now juniors, saw their prophecy made into flesh and blood.

“It was terribly chilling,” Lanae Merwin, now 31, of Hastings, Neb., recalled in a recent interview. “But, to us, it wasn’t totally surprising. We’d discussed it in class and it was happening. Though you don’t want a prediction like that to come true.”

Mr. Hofmann remembered having a similar reaction. “It was just strange to know that something was discussed not too long before that could actually happen,” he said. “Just a surreal feeling. To everyone else, it’s 8,000 miles away — no one cares. How can you grasp it? But to us, it was, we talked about it. For us, it was something that reached us directly.”

Years have passed. Mr. Walz left Alliance and moved to his wife’s home state, Minnesota; he is the only active teacher now serving in the United States Congress. His former geography students have moved as adults to Arizona, Nevada, Colorado and New York. Ms. Taylor lived in Poland for a while.

Now, in 2008, April has come again. It is, among other things, the month for genocide remembrance — the month when Rwanda was convulsed, when the Khmer Rouge conquered Cambodia, when Armenians commemorate what they call the Great Catastrophe, when Yom HaShoah, Holocaust memorial day, almost always falls. (Though this year, because of the Jewish lunar calendar, it will be observed on May 1.) The lessons of a classroom in Alliance 15 years ago still matter.

“You have to understand what caused genocide to happen,” Mr. Walz said, with those grim anniversaries in mind. “Or it will happen again.”