BERLIN — It was not his fame as a TV action hero nor his bulging biceps that enabled Carsten Stahl to bring a gymnasium teeming with chatty elementary school children to a rapt silence. It was his own, deeply emotional story.

Speaking the language of the street, in a thick Berlin dialect, Mr. Stahl began his presentation by coaxing the students to shout out the nasty things they say to one another on the playground. At each insult and profanity, the fourth- to sixth-graders packed onto benches in a semicircle around him erupted in laughter.

Then the 46-year-old father of two and former street gang leader told the children about a 10-year-old boy who for months endured insults that grew into threats and then beatings that ended with a group of bullies urinating on him as he lay at the bottom of a nine-foot pit on a bitter Berlin night, choking on his own blood, wanting only to die.

As Mr. Stahl spoke, a boy in a green T-shirt buried his face in his hands, and a girl with a long ponytail choked back sobs. But Mr. Stahl, who has told this story time and again to some 50,000 students across Germany, pushed on, his voice steady, his gaze piercing, and then delivered the well rehearsed climax.