UVALDE, Texas — The first shots came from the hallway outside the classroom. Arnulfo Reyes, a fourth-grade teacher at Robb Elementary School, quickly remembered the active shooter training he had rehearsed so many times and told his 11 students to lie under their desks and “act like you are asleep.”

A black shadow appeared at one of the classroom doors and a plume of fire flared from the tip of what looked like a rifle. Mr. Reyes felt a bullet piercing his arm, tearing off a chunk of flesh and bone. Then the gunman turned on the children. The rampage was so brutal and so swift, the teacher said, that he did not hear a single whimper from them as their bodies were shredded.

Mr. Reyes lay in a pool of his own blood for what seemed like an eternity until he heard police officers gathering in the hallway just outside the classroom door. His students lay silent, dead or dying; a few other children in an adjoining classroom were still alive, faintly calling for help. The officers will burst through and save us any minute now, he told himself. But the minutes ticked by, and no rescue came.

postponed entering the classrooms where the gunman was holed up — waiting some 78 minutes in a delayed response that a preliminary law enforcement investigation suggests was complicated by a search for a key and a decision to try to protect the lives of the responding officers.

“I kept waiting for someone to come,” Mr. Reyes said. “But when I didn’t see anyone coming in, I just thought, nobody’s coming.”

More than a month after the tragedy, as Mr. Reyes tries to recover from the severe wounds he suffered, the memories of that day play repeatedly in his mind. The day began with a jovial year-end award ceremony, after which nearly half of Mr. Reyes’s 18 fourth-grade students had gone home with their parents. Eleven stayed because they wanted to watch “The Addams Family” movie.

the students who died in his classroom that day, most of them barely 10 years old, he finds himself remembering them not in death, but in life.

Jose Flores, who lived for lunch and recess and was a “corajudo,” meaning he would get flustered each time he failed to understand a lesson or math problem. “He would shut down and I would tell him, ‘Don’t do that.’ And he did, he learned how to control his frustration.” Josecito, as his family called him, was named to the honor roll for the first time on the day he was killed.

And who could forget Jayce Luevanos? He was the popular class clown who reminded Mr. Reyes of the flamboyant movie character Ace Ventura portrayed by Jim Carrey. Jayce liked to wear a T-shirt with the image of an ice chest that read, “I’m a little bit cooler than you.”

On a recent afternoon, Mr. Reyes sat next to a blue folkloric cross given to him by the mother of Tess Mata, one of the victims, and a block of granite engraved with photos of all the victims. A cousin, Belinda Aguilera, stopped by to check on him. “He’s doing better, thank God,” Ms. Aguilera said as she studied Mr. Reyes, who was sitting alone on a couch.

Ms. Aguilera, who lives near the school, said she was one of the people calling Mr. Reyes’s phone in a panic after hearing several gunshots. “You popped on my head because I knew you were there,” she told him, fighting back tears.

“I’m so sorry,” she said. “I feel like my phone call made him do that to you.”

No, no, Mr. Reyes said, trying to reassure her at a time when practically everyone has lost any sense of assurance. This is not on you, he said.