The first thing they did a year ago at Public School 15, upon hearing word that the principal had been shot dead, was shut the doors. The killing of Patrick Daly was enough violation for the school in Red Hook, Brooklyn. The Sullivan Street entrance was first, then the exits on Wolcott and Van Brunt and Richards, the four corners of a tiny universe in peril.

No television cameras were allowed in to seek sound bites of heartbreak. The damage would be limited. What was alive and vital inside would be preserved.

"We were worried about the integrity of the building," said Mary Manti, the assistant principal, who has since succeeded Mr. Daly. The doors opened the next day, and 12 months after a senseless killing that threatened the worlds of nearly 1,000 children, that integrity remains intact.

One can still walk in any direction from the faded bloodstain on Center Mall in the Red Hook Houses and trace the lines of devastation. Madeline Daly still won't talk publicly about her husband's death. Florence Russell, the mother of one of the three young men sentenced to long prison terms for the killing, replays the events with as much anguish as anyone else. Many children are still haunted by the memory.

But perhaps the greatest truth a year later is that P.S. 15 has endured, and however cruel and heartbreaking the loss of the man, the legacy he left seems much bigger.

"The unthinkable happened: a meteor hit our school," Ms. Manti said. "And who could believe a school would have to face that?"

"The school is not the same," she said. "No school could or should be. Schools change. It's what they do. But I believe we have had a miraculous year. And we have changed in a very wonderful way."

That growth, with its aches and revelations, passed a milestone on Friday as a memorial Mass was held at Visitation Roman Catholic Church in Red Hook to commemorate the anniversary of Mr. Daly's last day. The 48-year-old principal was killed in a gunfight between teen-agers as he searched the neighborhood for a 9-year-old who had left the building that morning.

"If fear isn't the right word, then there certainly was apprehension after Pat's death," said William Casey, the superintendent for District 15. "It was impossible for any of us to know the toll it would take. But one of the spectacular things about the man and what he accomplished was that there was such direction to his plans. When he was killed, no one had to stop and ask where we went from here."

And so an ambitious program of integrating special-education students into general-education classes is in its inaugural year. And a conflict-resolution effort, teaching children to resolve disputes without violence, has been rethought and expanded, the children asked to carry its principles to their homes.

Paintings by third graders, the dividends of a hard-fought struggle to have a Studio in the School program financed for the first time, hang with an unpolished magnificence in the art room. The community programs run out of the school's basement -- job training, after-school care -- conduct themselves in intimate and affectionate coordination with P.S. 15.

Reading and math scores at the predominantly minority school went up last year. The hallways are spotless and hushed, the classrooms warmed by the soft electric hum of children at work.

As a result of a Dinkins administration initiative, P.S. 15 was designated one of the city's beacon schools and serves as a six-day-a-week, 12-hour-a-day community headquarters. Health workers, Girl Scouts, parents and organizers all swing through its doors. 'Simply Too Precious'

"There is a lot of anger still about the media coverage of Mr. Daly's death," said JoEllen Lynch, the director of the Red Hook Community Center. And the atmosphere "is pretty emotionally fragile," she said.

"The focus was on drugs and violence and another maligning of Red Hook. Our kids, the school's kids, again had to deal with this great perception that their community, their lives, were worthless. And the kids are simply too precious to have to deal with that. They are trying so very hard to grow up."

Mickey Correa, 11, still lives the pain of the process. Like other children and teachers and administrators, he sees a man round a corner and feels his heart race. He sees someone standing or leaning a certain way, that peculiar way the kinetic Mr. Daly did, and he begins to sprint. He stops, of course. But the sixth grader said he doesn't cry so much. Mickey, after all, read his own poem, "Time to Move On," on May 27, the day that P.S. 15 was officially renamed the Patrick F. Daly School.

"In the world right now there is nothing, but he wanted kids to keep struggling," Mickey said in a hallway last week. "He didn't want us to leave education."

Malik Jones, a sixth grader, was tempted to take a break from school this year. He said he didn't have homework when he did. He told his mother that school didn't feel the same. Malik, whose apartment in the Red Hook Houses overlooks the spot where Mr. Daly fell, watched yet another television program with film clips of urban violence and end with his principal's death.

Toni Jones studied her son. She had come to Red Hook with him years before and wound up joining him after school at P.S. 15 in a program to earn her general equivalency diploma. It had been Mr. Daly's idea, and when it had come time to take the test and the Government checks had been exhausted, the principal had shown up with a bag of tokens and $20. Ms. Jones is now an emergency medical technician. Socks in Big Shoes

"I told Malik to remember the gifts Mr. Daly had given him, to walk with those gifts, to carry them in his hands," Ms. Jones said. "The school was there; the teachers were. And Ms. Manti has been unbelievable. Mr. Daly left her big shoes to fill. But she's got some socks in there."

For her part, Ms. Manti wants no extra credit. She has 26 years in at P.S. 15, and she is doing as she and her predecessor always did. She says she feels his absence in the late afternoon when he might have made her a cup of tea and laughed about the day's events. But she feels him with her, with an instinctive, reinforcing instructiveness, whenever there is an education decision to be executed or a phone call to a parent to be made.

"People ask me about following in the footsteps of a saint," Ms. Manti said, smiling. "And they just don't understand. You see, I walked next to him when he was alive. There were no footprints to follow. All I had to do was keep walking."

Florence Russell walks through many days numbed by the events of a year ago. Her son is in prison. Her hopes are modest, even minimal.

"God is going to get everyone through it," she said from Florida before hanging up the telephone.

Jermaine Russell, who will be eligible for parole in 2012, is at Great Meadow Correctional Facility in Washington County, N.Y. He is in the barbering and beauty culture program. He calls his sister on Staten Island every day.

"In the beginning, he talked about Mr. Daly, but not so much anymore," said the sister, who spoke on the condition that her first name not be used. "He said he'd like to apologize to anyone, everyone. Mr. Daly was his principal. He was mine. He knew my whole family by their first name. He used to stand in the afternoons talking with my grandparents. If any of us had been able to see the future, see what happened, no one would have believed it then."

Disbelief still overcomes P.S. 15 occasionally. But it always surrenders to belief -- in the school, in its durability, in the building with its open doors. John Staniszewski, a music teacher in his first year at P.S. 15, calls the environment at the school "beyond anything I could have imagined or expected at a New York City public school."

When that school let out on Monday afternoon, Ms. Manti, ankle-deep in slush, held a child's hand in hers. She took the child home and then couldn't get back fast enough to the squat, not exactly unworn building. She walked past its murals, including the one in progress that will depict Mr. Daly.

"There is a spirit in the building the same as there is a spirit in a person," Ms. Manti said. "I ask myself all the time, do I still feel it? I do. And others tell me they do, as well. The anniversary is a very important time here. And for all the right reasons."

Photos: One year after the shooting death of Patrick Daly, above (NBC News), the principal of Public School 15 in Brooklyn, the school has endured and has been renamed in honor of Mr. Daly. (Ruby Washington/The New York Times); His widow, Madeline Daly, center front, joined teachers, pupils and parents at a memorial service on Friday in Red Hook. (Nancy Siesel/The New York Times) (pg. 45); "The school is not the same," said Mary Manti, the principal of Public School 15 in Red Hook, Brooklyn, who took over after Patrick F. Daly was killed. With her was Mickey Correa, 11, who read his own poem at the renaming of the school in honor of Mr. Daly. (Ruby Washington/The New York Times) (pg. 50) Map shows the location of the Red Hook Houses. (pg. 50)