Don’t let that long, fist-shaking title put you off. Although the show is performed by an energetic, fresh-faced cast of 13 teenagers, adults need not fear a series of droning monologues about the injustices and outrages visited upon youth. There is very little dialogue in “Once and for All,” which superficially resembles a free-spirited hour in the rumpus room. Angst-ridden invective is blessedly absent, although you might get assaulted with a little Silly String.

The show, directed by Alexander Devriendt, who conceived it along with Joeri Smet and the cast, essentially begins with the youngsters trooping casually onstage and seating themselves in chairs lined up in a neat row. Five minutes of messy horseplay follow. A couple of the boys pester one another using balloons like rubber bands. Two girls tip their chairs back, fall giggling to the floor and rope in a lanky boy to join their games. Another pair of girls constructs a pyramid from plastic cups, until somebody kicks it down in a fit of destruction. One girl is absorbed in a peculiar rite: burning Barbie’s feet with a cigarette lighter.

Just when the roughhousing threatens to reel out of control, an alarm bell sounds, and the kids scamper offstage, only to return a few moments later and enact precisely the same behaviors all over again. What seemed to be a spontaneous expression of unbridled energy is revealed to be a carefully choreographed ritual, bringing home the telling point that even in adolescence — make that particularly in adolescence — there is no such thing as being totally un-self-conscious.

Although the raucous music track favors loud rock and electronica, “Once and for All” generally presents its ideas gently. Behind its apparently casual, unstructured surface is a shrewd and compassionate understanding of the adolescent mind at work even as it is at play.

Variations on the group games range from the analytical to the abandoned. At one point the actors describe their behaviors rather than perform them. During another vignette they skulk onstage in what is clearly meant to be a state of heavy inebriation, each lost in a private world filled with fanciful or tormenting visions. In another sequence the communal fun becomes charged with the tenderness and anxiety of sexual exploration.

The sense of living your life in a fishbowl is never more potent than it is when you’re a teenager — unless you grow up to be a sports star, a movie idol or, God forbid, Paris Hilton. And so the action in “Once and for All” often jerks to a sudden halt, as the performers direct watchful, wary stares on the audience, the stand-ins for the disapproving parents and guardians. “I have to go too far,” one young woman announces, in one of the few, short monologues. No matter what time curfew is, she’ll be breaking it, she adds. How else to test the waters of adult responsibility?

“I’m confused,” a youngster behind me said, trying to discern a pattern as the kids kept pressing rewind and entering all over again. Well, exactly. Quicksilver changes in mood — from joyful abandon to sullen introspection to earnest thoughtfulness — are the stuff of adolescence, when hormones wreak havoc on the nervous system, and the future is both an open field you want to sprint toward and a black cloud enveloping the horizon. “Once and for All” embraces and emphasizes the contradictions of the developing mind, creating a vivid 3-D X-ray of the psyche in its formative years.

Parents might want to consider the light sexuality and the intimations of drug use in deciding whether to bring children 12 and under. (The show is also a participant in the un-family-oriented Under the Radar Festival of new and experimental theater.) But the tone of “Once and for All” is fundamentally innocent, and it is hard to believe that theater this honest, vital and fresh could do anyone any harm.

Much of the vitality and freshness springs directly from the performers, who are required both to embody the impulsiveness of youth and comment on it at the same time. Collectively and individually they are terrific, the roughhousing and the confessionals coming across as utterly natural. As anyone who has tried to act naturally in front of an audience can attest — this would include anyone who has ever been on a first date — it’s not as easy as it looks.

Of course as true-to-life as these adolescents appear to be, they depart from reality in one pronounced way that parents are sure to note. Unlike actual teenagers, after these kids have made an unholy mess of the place, they clean up after themselves.

ONCE AND FOR ALL

We’re Gonna Tell You Who We Are So Shut Up and Listen

Conceived and designed by Alexander Devriendt, Joeri Smet and the cast; directed by Mr. Devriendt; choreography by Mr. Devriendt and the cast; lighting by Jeroen Doise; sets and costumes by Sophie De Somere; sound by Stijn Degezelle; stage manager, Mary-Susan Gregson. A production by Ontroerend Goed, Kopergietery and Richard Jordan Productions, presented by the New 42nd Street and the New Victory Theater, as part of the 2010 Under the Radar Festival. At the Duke on 42nd Street, 229 West 42nd Street, Manhattan; (646) 223-3010. Through Sunday. Running time: 1 hour.

WITH: Charlotte De Bruyne, Edith De Bruyne, Febe De Geest, Jorge De Geest, Aaron De Keyzer, Christophe De Poorter, Edouard Devriendt, Dina Dooreman, Ian Ghysels, Barbara Lefebure, Fée Roels, Koba Ryckewaert, Elies Van Renterghem, Verona Verbakel and Nathalie Verbeke.