‘Idol’ threat

In the halls of Barnstable High School, they’re beginning to ask themselves what “American Idol’’ fans and judges may be wondering, too, as season nine of the Fox network’s star-making show unfolds.

Has 19-year-old Siobhan Magnus, a 2008 BHS graduate with no formal vocal training and little pre-Hollywood buzz behind her, become a legitimate top 10 contender? One of the favorites to wear the next “Idol’’ crown? What seemed unlikely a couple of weeks ago doesn’t seem so far-fetched today.

“There was a moment when Simon Cowell said to Siobhan (pronounced shuh-VON), ‘You’re a funny little thing, aren’t you?’ ’’ says BHS drama club teacher Ed O’Toole, who directed Magnus in numerous school productions. “Well, she’s got a lot of sides to her. She’s not the giddy little emotional kid up there onstage. America is getting to see that.’’

Magnus received the good news during last Thursday’s broadcast. Another finalist from Massachusetts, 22-year-old Ashley Rodriguez of Chelsea, didn’t fare as well. Considered the more polished of the two, thanks in part to her Berklee College of Music pedigree, Rodriguez failed to make the cut as the field was trimmed to 20.

The most striking difference between Magnus and Rodriguez was the emotional depth each brought to her make-or-break performance. Rodriguez seemed almost robotic while singing Leona Lewis’s “Happy,’’ whereas Magnus tackled “Wicked Game’’ by Chris Isaak, a surprising song choice in many ways, in much more soulful fashion. “Idol’’ judges took note, and so did 24 million viewers.

“The difference was right out there,’’ says MJ Santilli, who blogs about “Idol’’ on mjsbigblog.com. “One picked a really good song that not only showcased her talents, it made her seem interesting. The other picked a terrible song that was really boring.’’ Magnus, who sings again on tonight’s episode, now has a good shot to make the top 12, according to Santilli, which would make her the most successful local “Idol’’ finalist since Ayla Brown in season five.

In a phone interview after her “Idol’’ disappointment, Rodriguez expressed no regrets about her song choice, said she found the judges’ criticism “a little harsh,’’ and heaped praise on her fellow contestants, including Magnus. “Both being from Massachusetts and being in Hollywood together all day, every day definitely brought us together,’’ Rodriguez said. “I’ve watched the show for years, and this is the most talented and diverse top 24 I’ve ever seen.’’

So far, Magnus’s personal story has been largely under wraps as other finalists have gotten the showcase treatment. That, too, seems destined to change should she continue to garner voter support.

A few short weeks ago, Magnus was best known in her hometown for starring in lavishly produced school musicals - she played Dorothy in “The Wizard of Oz’’ her senior year - and for fronting an alt-rock band called Lunar Valve, which plays local clubs and dances in the Hyannis area.

At BHS, where Magnus also performed in several Shakespeare productions, drama is taken as seriously as any varsity sport, maybe more so. Her teachers and peers aren’t surprised that Magnus has appeared comfortable and focused while on a huge national stage. “Singing or acting, Siobhan’s an instinctive performer,’’ says O’Toole. “It’s like watching Willie Mays. She works hard but makes it look easy.’’

Magnus hails from a large, blue-collar, Irish-American family - including three older siblings, two younger ones, and 17 cousins - blessed with artistic talent, according to friends and family members. Two of her uncles are professional musicians: Alan Ware, drummer and coproducer for the Boston-based Ultrasonic Rock Orchestra, and Tracy Ferrie, bass player for the metal band Stryper. Her father, Alan Magnus, has also sung with local bands. Rory, an older brother, is a video animator. (“Idol’’ contestants and their family are under agreement with Fox not to grant interviews.)

In a video essay on the 2008 “Oz’’ production, Magnus says she likes to act “because I can pretend to be somebody else’’ and because it’s “an escape’’ from the more stressful parts of her life. Those parts have included helping to raise two younger sisters while her father was coping with an unspecified disability.

In another video, posted on the “Idol’’ website, Magnus credits her mother, Colleen, with encouraging her to audition in Boston last summer. Figuring she had nothing to lose, Magnus says, she counted on being able to differentiate herself from other contestants by dressing in a somewhat funkier fashion (which she has) and by bringing a blues-soul vibe to her performing (which she also has). Among her musical idols is Janis Joplin, whose songs she’s covered with Lunar Valve.

“Siobhan is incredibly driven; she knows what she can do and prepares herself 100 percent,’’ says Stephanie Gianno, a close friend who joined Magnus in Hollywood last week to provide moral support. “What’s happened to Siobhan already is very surreal to her. She’s still taking it day by day.’’

Ironically, Magnus applied to Berklee last year and was put on the waiting list. But Ware says her lack of vocal training may be an asset right now. “Her singing isn’t being guided into a certain shape,’’ he says. “Siobhan doesn’t put on any airs, either, yet she knows how to deliver a song. She’s not bound by any rules.’’

Watching last Tuesday’s show, Ware was struck by how many female vocalists were criticized for their “pitchiness,’’ a result of being too nervous, perhaps. Magnus showed none. Says Ware, “She’s very mature and won’t let things get to her head either way, criticism or praise.’’

Should Magnus make it through the next several weeks, “Idol’’ viewers will likely pick up more biographical tidbits: that she loves cats, the Red Sox, and ice hockey; that for the past three years, she’s worked as an apprentice glassblower at Morrison Glass Studio in Hyannis; and that she likes gory horror movies and costuming friends as zombies and werewolves for Halloween.

“I have a pretty good tolerance for pressure,’’ Magnus says on one video. “Idol’’ fans will be watching closely as the pressure increases, none more intently than the ones back home on Cape Cod.

Joseph P. Kahn can be reached at jkahn@globe.com.