ATLANTA—”;Pick your head up, buddy,”; Tom Dunn said to Darius Nash, who had fallen asleep during the morning's reading drills. “;Sabrieon, sit down, buddy,”; he called to a wandering boy. “;Focus.”;

Dunn's classroom is less than three miles from his old law office, where he struggled to keep death row prisoners from the executioner's needle. This summer, after serving hundreds of death row clients for 20 grinding, stressful years, he traded the courthouse for Martin Luther King Jr. Middle School.

The turmoil of middle school turns many teachers away, said the school's principal, Danielle S. Battle. Students' bodies and minds are changing, and disparities in learning abilities are playing out. “;A lot of people will say, 'I'll do anything but middle school,”;' she said.

But this is precisely where Dunn chose to be, having seen too many people at the end of lives gone wrong, and wanting to keep these students from ending up like his former clients. He quotes Frederick Douglass: “;It is easier to build strong children than to repair broken men.”;

The school has institutional architecture that brings prisons to mind, but Battle has warmed it with colorful paint and brighter light. Ninety-three percent of students are black and 5 percent Hispanic; some 97 percent qualify for free or reduced lunch.

“;I just walked in here and fell in love with the place,”; Dunn recalled. His day begins at 8 a.m., when he stands by the school's buzzing metal detector, checking bags, as nearly 600 students file through in a half-hour. It is not a popular job, but he uses the time like a politician working the plant gate at shift changes. Saying hello with a smile, he taps the bags, peeks inside, sends the kids along. But he is also no-nonsense, with a “;hey-hey-hey!”; to pull back the ones who try to slip around the detector. Battle drops by to greet the students.

As a lawyer, Dunn said, he saw his job as “;telling stories,”; to help judges see each client as a human being who may or may not have done terrible things, but who suffered wrongs at trial or earlier in life—and who deserved fairness under the rule of law, perhaps even mercy.

He told clients' stories during his service as defense counsel in the Army Trial Defense Service, in Florida, in New York state and most recently at the Georgia Resource Center, the nonprofit law firm he headed. Though the center does not keep a scorecard, the strategy has resulted in delayed executions, commuted death sentences and even overturned convictions, said Brian Kammer, who took over as executive director.

“;If you're just talking about the legal niceties of the case, you're boring the heck out of the audience,”; Kammer said. “;You're squandering the moral force of your argument.”;

After decades of accumulating such stories, Dunn said, he recognized a common thread: the lack of a supportive authority figure like a teacher, of a helping hand that might have meant “;the difference between a good life and a ruined life.”;

Illness forced his decision to leave the law. In 2006, he ignored a sore throat and worked through two months of grueling hearings in four cases back to back. Bacteria entered his bloodstream, causing toxic shock; the infection caused deterioration in his spine and led to congestive heart failure. He recovered, but not fully; this year, Kammer recalled, Dunn met with the staff and said: “;I have the heart of a 70-year-old man. If I continue to do this work at the level I want to do it, I'm going to die.”;

The same day that he left the center, he showed up at the Atlanta training program of Teach for America. During his training, he focused on special education, recalling that he saw learning disabilities “;in nearly every case”; on death row. He now works mainly in classrooms that blend special education students with the general population.

When he interviewed with the administrators at King, though, he encountered skepticism. “;I was just baffled by why he'd want to come here,”; said Barbara Shea, an assistant principal, standing with Dunn as the hallways cleared and an afternoon class began. “;I tried to warn him—I wanted him to understand it was not an easy job.”;

Across the hall a classroom door opened, and the teacher pulled a tall, angry student out by his arm and asked Dunn for help. “;He's having a Taylor moment,”; Shea said, referring to a girl in the class. “;He wants to sock her in the mouth.”;

The boy walked toward the exit, but Dunn argued him back to a chair where he sat, stormy and silent. Dunn talked softly to him, helping him to settle down.

As Dunn walked back down the hall to his office, he chuckled at the thought that Shea might have thought of him as a dreamer. “;You can't be a starry-eyed idealist and do defense work in capital cases for 20 years,”; he said.

Propped against the wall in the office—actually, a converted teacher workroom that his colleagues pass through to get to a restroom—is a clipboard with a paraphrase of a quote from former Justice Harry A. Blackmun of the U.S. Supreme Court: “;From this day forward, I no longer shall tinker with the machinery of death.”; It was from a dissent in a 1994 case in which the justice argued that “;the death penalty experiment has failed.”;

Dunn was in the office in August when he got word that the Supreme Court had ordered a lower court to reconsider the case of one of his best-known former clients, Troy Davis. At that moment, being out of the game was “;really hard,”; Dunn said.

But in the classroom, there is no hint of regret. In the afternoon, a student, Shamon Nations, abruptly asked, “;What made you come to school and give up your other job?”;

He replied, “;Because I love you guys.”; Somehow, it does not sound saccharine.

Shamon was not satisfied. “;Yeah, but what about the money?”;

“;I made a lot more money last year,”; Dunn acknowledged. “;But it's not about money.”;

Between classes, as he walked down the halls and the class bell rang, he stopped stragglers who might be tempted to keep wandering. “;Hey, buddy,”; he asked one. “;Where are you going?”; He slipped an arm around the boy's shoulder, and used it for leverage to give a gentle shove in the right direction.