Neither did he have a pulse but that did not stop the doctors from inserting a tube into his groin to replace the blood he was losing, and then to open his chest in the hope of restarting his heart — which turned out to have three or four holes in it, Dr. Goldberg said. She held up a stainless steel rib-spreader.

As the details of Lamont’s story unfolded, one girl struggled to keep her composure. Another hid her face in her friend’s shoulder. Lamont died about 15 minutes after arriving at the hospital, underscoring that prevention of gun violence is a lot better than trying to cure its effects, Dr. Goldberg concluded.

“Who do you think has the best chance of saving your life?” she asked the students. “You do.”

Despite the grisly images, most of the students said afterward that people should still be allowed to own guns for self-defense, although not assault weapons. Mahogany Johnson, 14, said she is in favor of a street ban on semiautomatic weapons like AK-47 assault rifles, which she said should be used “only in the woods.” Jabriel Steward, 14, said, “Everybody should be allowed to have one gun for protection, for self-defense.”

But Feliciana Asada, 14, said more students should be given the opportunity to participate in Cradle to Grave. “Programs like this need to be installed in schools,” she said.