On-set report: High School Musical 3

Disney's all-singing, all-dancing High School Musical has captured the imagination of children around the world. Starting out as a made-for-television film, it is now a multi-million-dollar brand. As the third instalment comes to the big screen, Craig McLean goes on set to investigate the phenomenon

Sunday night at Salt Lake City's East High school, and it is the final basketball game of the season. In the huge, 2,500-capacity gym the home team, the Wildcats, are facing the Knights. The tiered seats are filled with screaming fans. The cheerleaders are thrusting and kicking, the team coaches gesticulating and shouting. On the court, player number 14 grabs the ball, feints to the left, passes the ball, runs on, catches the return pass, leaps on to a trampette and dives balletically for the hoop. The ball bounces off the backplate. Number 14 hurtles face-first towards the floor. A blue crashmat breaks his fall.

The screaming in the gym reaches ear-shrivelling pitch, and the energy crackles in every direction. Which is remarkable considering that it is some time after 1am and they have been doing this - the screaming, jumping, shouting, shooting, falling - for almost 12 hours. And they won't finish till almost dawn. Thank goodness they are not playing the accompanying music yet. Then, after a quick rub with a towel and a quick spray with a water-spritzer, number 14 does it all over again.

It is June 2008 and on the set of High School Musical 3: Senior Year the filming is reaching fever pitch - not least because this movie is being made on an ultra-tight deadline, with a very fast turnaround, to meet a release date less than five months away. Everyone, cast and crew and extras, is tired but buzzing with exhilaration. The all-powerful, feelgood alchemy of High School Musical (HSM) transforms fatigue into esprit de corps.

'It's been pretty insane hours, but it's good - we're nocturnal,' says a beaming Corbin Bleu, who plays Chad, the number 8 basketball player-cum-skilled chef. 'We did this [song-and-dance] number about three weeks ago and we had 2,500 extras. It was,' he says, 'insanity.' Indeed: the deftly choreographed basketball shot I watch them filming over and over again amounts to approximately 12 seconds of screen time.

Then again, most things to do with this staggeringly successful Disney film series happen at fever pitch. Everyone knows this: the young actors, chief among them Zac Efron (who plays the number 14 basketball hero and Chad's best buddy, Troy) and Vanessa Hudgens (his peachy, maths-champ girlfriend and singing partner Gabriella, who is, seemingly, his off-screen partner, too), who have been catapulted to global fame by HSM; the tween and teen audiences who have made these candy-coloured fairystories about song, dance, friendship, teamwork, love and being true to your school the defining children's pop cultural phenomenon du jour; and the top brass at Disney, who have leveraged what began as seemingly just another made-for-television film into an international, multi-platform, all-conquering, cash-cow brand.

The cast are multi-ethnic and super-cute. Most of the typical school 'tribes' are represented - the maths whiz, the sports jocks, the bitch, the chubby one, the geek, the musos - although none of the notionally negative qualities, of course, are that extreme. The snooty fashion-forward queen-bee Sharpay (played by Ashley Tisdale) is never too bitchy.

While it is not OK for the characters to be too scheming, weird or dysfunctional, it is OK for the actors to be ultra-glamorous: Efron - who has just completed filming a role in Richard Linklater's new movie - has become perhaps the biggest teen idol in the world (even though he is 20 now), and has the biceps and the sexy Rolling Stone cover shoot to prove it. HSM3 is still a children's film, but with the characters being on the cusp of adulthood, Disney can afford for them to appear a little sexier.

The first film in the series, initially broadcast on the Disney Channel in January 2006 and repeated endlessly ever since, was seen by a worldwide audience of 200 million in one year. The accompanying soundtrack was the third bestselling album in the world in 2006. A 42-date concert tour of North and South America, featuring the actors singing songs from the film, grossed $25million.

When HSM2 premiered on the Disney Channel in the US in August last year, 17.2 million people watched - the most viewers ever for a cable TV programme. The original films have been dubbed and adapted for local markets around the world; China and Russia are making their own versions. Aside from myriad merchandise tie-ins there have been three successful touring productions of High School Musical On Ice.

A stage play toured Britain earlier this year and is now playing in London's West End. HSM creator and producer Bill Borden remembers making available the licence for independent theatrical productions of the first film. 'Annie, which is the most popular stage play ever put on by schools or community theatres, has about 400 requests a year,' he says. 'We got 64,000 requests in two weeks.'

With High School Musical 3: Senior Year, the stakes are higher still. Narratively, it is the climax of the trilogy. Our spunky young heroes and heroines are facing the prospect of graduation and college - how will that affect friendships and relationships? 'It's a coming of age story,' says Kenny Ortega, the director of all three productions. 'As it says in the script, "You don't take the girl with you after high school."'

HSM3 is the first of the series to be released in cinemas, which means a whole other level of marketing and strategising - as one Disney executive told me during my set visit, 'Before there was a script there was a release date.' The budget that Ortega has to play with has quadrupled from HSM2's $7million (he had $4.5?million on HSM1) to $30million. 'Detail and dimension matter more,' he says of the leap to the big screen.

Specifically for this 57-year-old choreographer turned filmmaker, this means cramming 14 song-and-dance numbers into the film, many of which reference the icons and talents he has grown up and/or worked with: Gene Kelly, Bob Fosse, Michael Jackson, Busby Berkeley, Fred Astaire. 'We have three or four technical, huge-scale, Broadway numbers, in four minutes of film time,' the production designer Mark Hofeling says.

'I think music's a universal thing,' says Hudgens, who has parlayed her HSM profile into a promising recording career. 'I grew up watching musicals and I loved it because it's a journey that you don't see very often. It's a world where the story is moved along by music and dance. And it's a very magical one. Who doesn't love watching that?'

As one might expect from the global capital of the Church of Jesus Christ of the Latter-day Saints - the Mormons - Salt Lake City is a pristine, clean and polite city. It is also a great filming location: it is only a two-hour flight from Los Angeles; the local and state authorities provide tax assistance to productions; and topographically, it offers everything. As Olesya Rulin (whose character Kelsi is a bespectacled, piano-playing clown/mascot/klutz, but in reality is a ravishing and assured young actress) says, 'We have desert, lake, mountains, sand dunes, salt flats, all 40 minutes away from each other.'

Another local quirk: Utah's original superstars, the Osmonds, set up a studio complex in the nearby city of Provo, which has provided a wellspring of musical and technical talent. 'Our crew is 99 per cent local,' Borden says. The result is that Disney makes, and sets, many films in Salt Lake City. For a change they opted to nominally set HSM in the topographically similar New Mexico.

The location manager Carole Fontana helped Ortega scout the school - he was particularly taken with the size of East High's gym, and the spectacularly tiered cafeteria. 'It's so well suited to the Busby Berkeley idea of making mountains out of people and using environment to its absolute apex,' Hofeling says of the cafeteria in this 'idealised' vision of a school building. 'Which is very Kenny.'

Bill Borden knew Kenny Ortega from way back: they met on the set of Francis Ford Coppola's 1982 cult musical folly One from the Heart. Ortega was a choreographer working with Gene Kelly, Borden a young PA (there is a nod to this first meeting in HSM3 - it features a dance scene set in a junkyard, as Coppola's film did).

Borden went on to become a successful producer - he worked with the director Taylor Hackford on the musicals La Bamba and Hail! Hail! Rock'n'Roll - and a father of three young boys. 'We'd sit down on a Friday night to watch a movie together, and as a family, we kept coming back to The Sound of Music, Hairspray…'

He decided to make a musical that would appeal to his children. 'They liked rock'n'roll, and they liked pop. What they didn't like were Hollywood and Broadway show tunes.' In any case, Borden could not afford to compete with the Hollywood producers, who were buying up Broadway hits such as Sweeney Todd, Chicago and Rent. 'I had to make my own musical, and my own music.'

Most musicals are written by one composer. Borden did not have time for that. He would hire 10 writers from the contemporary pop world to write 10 songs, and he would allow them a month to come up with the goods. Having analysed the architecture of musicals, he gave them strict briefs: he needed an introductory song, a curtain call song, a finale song, two solos (one by each lead), a comedy song and a four-handed song. 'So right away you've got eight or nine songs that are structurally defined by the nature of the story.'

Borden also had the concept of that story: a high-school musical (the working title was so simple and strong that they kept it), and he hired a writer friend, Peter Barsocchini, to flesh it out. It is a genre synonymous with one movie: Grease. Was Borden confident his film could outpace the long shadow cast by that 1978 classic?

'You know, I was not confident. But it really is not a spin-off of Grease. People have asked me that [but] it wasn't one of my influences. Zeffirelli's Romeo and Juliet was more an influence on this movie. I figured if you're going to borrow themes and ideas you might as well borrow from Shakespeare. Romeo and Juliet: couple are together, they're apart, put it into three acts…'

Why did Disney greenlight Borden's idea? The producer cites two reasons. Firstly, in 1991, he made Backfield in Motion, a television film for ABC about American football set in high school. It was a huge hit, and is still broadcast every year during the football season. Gary Marsh was a junior executive at ABC at the time of the original production - he is now the president of Disney.

Secondly, the Disney Channel had had great success with the musical trio the Cheetah Girls, a book series turned film turned touring act. 'And Gary was thinking there was a chance to make money on music.' Borden figured out that one too. 'I knew from the beginning that this type of movie had many platforms - it could go out as music, as stage plays…'

Then there is the contribution of Ortega. Even on a film set teeming with hundreds of teenage extras - and all the noise that goes with them - Ortega is a charismatic and loud figure. In the gym he marshals the bleachers full of teens with fatherly encouragement, even though he is barking it through a microphone. During a run-through of one of the songs he shouts, 'Don't just lip-sync, sing! I wanna see the spit!'

All the cast clearly look up to Ortega. 'Every single detail and every single person matters,' Rulin says. 'You'll hear him say to the extras, "You are just as important in this movie as the main cast or any of the stars." And he does a great job with that. And that's why the movies are so successful - he goes to each of us and gets our opinions and lets us interpret our own themes into it. But he also teaches us to love it and make it our personal goal to make this a hit, too.'

Such detail is crucial to understanding the success of HSM. From the micro to the macro, everything is worked out. 'We cannot wear one costume or pick one hairstyle or say one line that isn't approved on a number of different levels,' Coleman says. 'Disney don't let anything go.'

On HSM2, Troy and Gabriella have a picnic - the sandwich filling (peanut butter and jelly) was chosen by Disney Channel viewers. On HSM1 Zac Efron's voice wasn't deemed strong enough for him to sing alone, so his voice was part-dubbed by Andrew Seeley (Seeley didn't appear in the film but he did take part in the concert tour). 'I think it worked,' a sanguine Efron says, although he adds that 'you can tell' the instances where their voices were blended together.

High School Musical 3: Senior Year finds 'the six' - Troy, Gabriella, Chad, Taylor (Monique Coleman), Sharpay and Ryan (Lucas Grabeel) - leaving school. What happens next to the franchise? College Musical, for example, would suggest a somewhat riskier and rather non-Disney proposition. Enter, instead, plans for HSM: The Next Generation.

Joining the cast of HSM3 are three new, younger characters. One of them is played by Jemma McKenzie-Brown, 14, from Hull. She is a student at London's Sylvia Young Theatre School, and already has a part in the television drama The Amazing Mrs Pritchard on her cv. Borden acknowledges that the idea to audition in Britain came from the president of Disney.

'He knew we wanted to seed the show with some new people, to introduce the new generation in this picture. And he suggested with the popularity of the show in Europe, especially in England, that we look to see if there was an actor that would fit.'

The simple fact that auditions were being held in Britain would increase the buzz in that market. McKenzie-Brown's casting led to the scripted character, Tiara, becoming an English transfer student. 'Jemma had magic,' Borden says. 'In terms of her being an actress and a personality and how she sang and danced, she really was a perfect fit.'

'They are different to how I imagined,' says McKenzie-Brown of HSM's existing stars. 'I thought they would be clichéd celebrities, really diva-ish. But they're all really nice.'

Why does she think British children like the High School Musical movies so much?

'I always like American high schools better because they wear their own clothes, and everything looked funner [sic]. But because the whole movie is about people coming together from different backgrounds, and coming together with theatre, that's why so many countries all over the world like it so much.' Or, as Ortega puts it, 'this is part of America that all the other places can connect to.'

Around 2.30am, as I finally leave the HSM3 set - a cauldron of excitement, volume and hormones - myriad other reasons for the franchise's popularity flash through my head. The diligence and thoroughness of Kenny Ortega, who is still geeing along his extras at this late hour. The catchiness of the songs. The spectacle of the choreography. It all adds up into a winning formula. One that works on many levels.

My five-year-old son and six-year-old daughter love re-enacting the instantly appealing song-and-dance numbers that come along at very regular intervals in the narrative. My 13-year-old loves the excitement, colour, fashion, drama and gorgeous people thrown out by this whirlwind of a secondary school. And I love the sheer entertainment value of this straight-up-and-down fun-fest - no ironic detachment required.

Olesya Rulin, 22, studied marketing and psychology at university and had made five Disney films before HSM. She offers this explanation: 'Disney is like this marketing machine. It's very successful because it markets childish enthusiasm. What nation, what person, doesn't know that? You know what it feels like when you're a kid of three or five, to dance, to run around, and sing and dance grow in your own personal character. That's why High School Musical is so addictive and easy to watch - you kind of forget about reality for an hour and a half. Same with any other Disney movie: it's dreams, it's fairytale, it pulls you away of the idea of, "Hey, we're at war" and all these other issues. For an hour and a half you're happy and you're a kid again and life seems to be OK. And that's what they're so good at.'

• 'High School Musical 3: Senior Year' is released on October 22