“Asphyxiation games have been with us for generations, but what makes the current generation’s execution of this game different is that more kids are willing to play it alone,” said Dr. Thomas Andrew, the chief medical examiner in New Hampshire, who has consulted on 20 cases around the country where the game was suspected.

Of those 20 cases, most of which were listed officially as suicide, Dr. Andrew said he became convinced that four were really accidental from the choking game, and two others were unclear enough that they should have been changed to an undetermined cause of death. But he said that none of the death certificates, to his knowledge, were changed.

Anxiety about sex is another entanglement in the discussion. In some older teenagers and adults, the game can become associated with autoerotic practices of masturbation or intercourse to intensify orgasms, though Dr. Andrew and other experts say they think sex is not a factor for younger teenagers — and there was also no sex or ejaculation in Levi’s case, his mother said.

For now, most of the new debate is driven by advocates like Scott S. Metheny, an intense police officer from Upper Moreland, Pa., a suburb of Philadelphia, who has done more than 140 antichoking game presentations in the past 18 months on his own time.

He flew to Texas to talk to the students at Navarro, about 40 miles northeast of San Antonio, and to introduce Levi.

“Bringing Levi in was a shock factor,” Kandi Knippa, 18, president of the Drug Awareness Council, a student group. “It was very intense. But if we can save one life, it was worth it.”

Image Above, Kelly Mitchell, 12, left, and Kaitlyn Murphy, 14, students at Navarro, listened to a program about a game that involves choking. Credit... Michael Stravato for The New York Times

About three-quarters of Ms. Knippa’s classmates, girls as well as boys, raised their hands when asked if they had heard of the choking game, which Mr. Metheny said was typical.