"To put on a charro suit, it just feels right," says Mr. Escobar Bravo. "It's your roots."

Escobar Bravo stands in the cement courtyard of the School of Mexican Music, the only conservatory in Mexico City that teaches traditional folk music - the Juilliard of mariachi. He's waiting to join a dozen other students ranging in age from teens to seniors for a two-hour workshop. The building, an old silk factory, stands in one of Mexico City's most crime-ridden neighborhoods. But from its pastel-blue walls emanate the sounds of salterios and marimbas - traditional folk music the school hopes to preserve and expand.

It might seem odd that an institution in Mexico - the birthplace of mariachi - needs to promote the genre. But, in fact, that's what it's doing - and, in the process, is somewhat at war with the country's own pop music culture. Mariachi music today is undergoing a worldwide renaissance. Once simple street musicians, mariachis have turned into mainstream pop stars celebrated from Tijuana to Tokyo. They play with world renowned symphonies. In the US, hundreds of public schools now offer mariachi classes.

But along with the music's popularity have come glitzy adaptations, commercialized products, and often embarrassing wannabes. Purists consider some of today's sounds no closer to traditional mariachi music than the rock opera "Tommy" is to "La Boehme." Thus the conservatory's quest to turn out a generation of artists schooled in the old ways.

"Mariachi is getting so modern," says Daniel Garcia Blanco, a sprightly septuagenarian who founded the school in 1990 as an alternative to the classic conservatories of Bach and Beethoven. "We teach it the way it was."

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Students mill about the old warehouse roofed with corrugated metal, their guitars and bongos in hand. Some 200 are enrolled in programs that last from one to three years. Some want simply to be able to play music at home. Others, like Escobar Bravo, dream of becoming professional musicians. Many know they'll never be famous, but see their instruments as their closest companions.

"For we musicians, our instruments are like a girlfriend: They won't respond to nothing, you have to give them care," says Isidro Roman, a student who works part-time at a law firm as a messenger.

The school's mariachi class has all the elements to form an ensemble: violins, Spanish guitar, a small five-string guitar called a vihuela, a guitarrón or bass, and trumpets. The class plays traditional sones (music from the western state of Jalisco) and is at turns both lively and melancholic, depending on the theme: love and unrequited love, war heroes, tragedy, patriotism. Though the image of mariachi is middle-aged men strolling in plazas, many of these students are women. At least half are young.

On a recent evening, Escobar Bravo sits slouched against the wall, as if his parents made him join mariachi class against his will, but his posture belies a deep dedication. At age 14, the most un-Mexican band - the Beatles - made an impression on him, and he asked for a guitar. His mother is a singer, but at age 16 he went to work for his father in an auto-parts shop.

Now, as he tries to balance work and art, he labors in the store from 8 a.m. until 2 p.m. and then heads to school. A third-year student, he takes 20 hours of classes a week, and practices his guitarrón at least two hours a night. He performs in a restaurant with a group on weekends - for free. "You have to sacrifice a lot: going out at night with friends or family events," says Escobar Bravo.

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IN THE PLAZA: Singer Isabel Montero performs with Los Galleros in Guadalajara City, Mexico during the International Mariachi Festival. GUILLERMO ARIAS/AP

Once rejected by Mexico's uppercrust, mariachis became national icons in the 20th century - bolstered by their role in movies. In Mexico City, tourists flock to Garibaldi Plaza nightly, where mariachis have congregated for almost a century. Outside the country, mariachis play everywhere from orchestra halls to children's baptisms. They're contracted for weddings, funerals, and birthdays. Musicologists attribute the genre's global spread to its emotional range.

"It is one of the few music forms that marks the entire human life cycle, from birth to death, and everywhere in between," says Daniel Sheehy, director of Smithsonian Folkways Recordings in Washington and an expert on mariachi.

As more people play, though, the sounds that come out of the vihuelas and violins don't always satisfy the purists. In Garibaldi Plaza, musicians say they're inundated with "imitators" who play poorly and sometimes turn out to be "thieves." "They might be taxi drivers during the week, and then on the weekend they come and put on a charro suit," huffs Juan Manuel Cruz. "I am a son of a mariachi. The pirates humiliate and denigrate us."

Efraín Reyes Perez, general secretary of Mexico City's mariachi union, says his group counts 1,050 members and more than 2,000 imitators. In November, the union will relaunch a program requiring mariachis to hold city-certified credentials, "so that wherever we go, we represent Mexican folklore," says Mr. Reyes Perez, a guitarrón player, "not robbery."

At the conservatory, musicologist José Luis Cerón Mireles complains that arrangers of mariachi today often add faddish twists to traditional compositions. He says mariachis have simply become "adornments" to sell music, which adversely affects young people learning the genre. "They just want to play the successes, the stylish music," he says, "whatever the stars are singing."

The conservatory's goal is to teach basic skills such as reading music, theory, and history and to provide a repertoire of classic music. But even the school doesn't dominate the moral high ground in the debate over what's authentic. Some musicians in Garibaldi Plaza doubt a school, even a well-intentioned one, can teach the art properly. They note it is something that has to be handed down through generations. "You have to feel mariachi to play it," says Mr. Cruz, a freelance musician.

The sound is just different, he insists. "Here, if I kiss a woman, I do it with passion," interjects his colleague, Erik Hernandez, pretending to dip a woman in the air. "In the US it's like this," he says mimicking a peck on the lips.