In late 2005, executives at the Disney Channel were caught off-guard. The cable channel had high hopes for High School Musical, one of its Disney Channel Original Movies (DCOMs), among the target demographic of so-called “tween” viewers, kids between ages nine and 12. The film, directed by Kenny Ortega, had slick choreography, original pop music, a diverse cast and palpable romantic chemistry between stars Zac Efron and Vanessa Hudgens. But no one, according to a new book on the millennial-beloved cable channel, expected it to transcend kids programming, long considered a cultural backwater both within and beyond Disney. “Despite what some executives later tried to say, that they saw it coming, they did not,” said Ashley Spencer, author of Disney High: The Untold Story of the Rise and Fall of Disney Channel’s Tween Empire. “This caught everyone by surprise.”

Within weeks, High School Musical was a bona fide cultural phenomenon, and a new, unprecedented gold standard for the business potential of kids programming. Along with tweens, younger kids and older teens were obsessed with its stars. The soundtrack topped the Billboard 200 and became the bestselling album of the year of any genre. By the end of 2006, more than 90 million people in more than 100 countries had seen the movie; a whopping 17 million people (myself included) tuned in for the premiere of the sequel. And more crucially for the company, the franchise generated revenue for Disney across 10 different divisions – theme parks, home entertainment, merchandise, a licensable theater show, among others.

Spencer identifies the High School Musical boom as the peak of the Disney Channel’s power – a haphazard, trial-and-error rise that culminated in the kind of cultural ubiquity and cachet any company today would kill for. Concurrently the channel’s talent became synonymous with mainstream, bubbly, at times oppressive stardom – Hannah Montana’s Miley Cyrus, Wizards of Waverly Place’s Selena Gomez, Camp Rock’s Demi Lovato and the Jonas Brothers. “Even if you weren’t a kid then, even if you didn’t have kids then, [Disney Channel] became so big that you know what that means,” said Spencer. “Most people can conjure in their mind an image of a brightly lit sitcom with loud colors and a perky kid. It became ubiquitous, and it created something that a generation rallied around.”

The cultural significance of the Disney Channel is self-evident to anyone coming of age at that time, one deep in viewers’ brains and floating in snippets around social media but not recorded in a serious, chronological business history. “I couldn’t believe it hadn’t been done before,” said Spencer, a former Disney Channel kid from central Florida turned culture journalist. “For a certain age group, it’s so obvious – of course there’s a story to be told here.”

Disney High goes behind the scenes of the erratic rise of the cable channel, featuring interviews with many current and former Disney Channel executives, producers, directors, writers, actors and crew who witnessed the channel’s frictions within the company and its notoriously heavy-handed censorship team in real time. Though it was founded in 1983, Spencer starts the story in 1995, with the hiring of Anne Sweeney, a former Nickelodeon executive, as channel president. Sweeney, then 38, was tasked with turning what was essentially a channel with little kids shows, or musical shows whose talent graduated too early (the Mickey Mouse Club), into competition for the dominant kids network of the era.

Sweeney faced an uphill battle, both within the company, where it was viewed as small potatoes, and in the larger cultural consciousness, where Nickelodeon held kids’ attention as a brash, parent-free zone. “Disney was not a cool brand for a 12-year-old in the 90s,” said Spencer. It was associated with kids’ animated movies and theme parks. “So when you’re 10, 11, 12, and you’re wanting to start to be cool, and you love pop music and you want to watch MTV, but also it’s scary and your parents don’t want you watching TV – Disney Channel smartly tapped into that.”

Despite internal opposition, Sweeney and her team pursued programming that tweens and parents could watch together, with snippets of the pop music zeitgeist at a level deemed safe enough for kids. The channel started playing Britney Spears, ‘NSync and other boy bands’ music videos. It developed light comedic shows with diverse tween protagonists handling mundane coming-of-age struggles – So Weird, The Famous Jett Jackson and Even Stevens. Instead of ad breaks, the channel aired “interstitials” promoting the company’s theme parks, theatrical releases and, eventually, its cheaply produced, highly rewatchable DCOMs such as Zenon: Girl of the 21st Century, Johnny Tsunami and Cadet Kelly.

Disney High delineates its chapters by show and/or movie, as the channel became increasingly defined by its homegrown “triple threat” stars. Hilary Duff, from the seminal series Lizzie McGuire, became a charting pop icon to a certain slice of millennial girls. Raven-Symoné, the Cosby Show child star turned That’s So Raven anchor, broke ground as a curvy, Black sitcom lead, and scored a pre-HSM hit with The Cheetah Girls. By the time the network hired Miley Cyrus, in 2006, to play a regular girl by day, singer by night in Hannah Montana, the wheels had been greased for talent to expand beyond their show, even eclipsing the company’s power as a touchstone for a new generation of pop stars.

Such exposure was a massive burden on young talent, and Disney High recounts the network’s increasing difficulty with (micro) managing its stars. The adults in the room were, in broad terms, ill-equipped to help with increased tabloid scrutiny, near-constant surveillance and internet chatter, from Cyrus’s controversial Vanity Fair cover, to the relentless press Gomez faced for dating Justin Bieber. The final chapter covers Lovato’s well-documented mental health struggles in 2010, which the network seemed loth to address lest she stop working, and which culminated in them severing ties with her after she entered rehab.

Along with Lovato’s documentary Child Star, out this month, Disney High further illustrates the conundrum of child star – big dreams, bigger pressure, great risk and potential when a child becomes a business. “This is such a strange situation for a kid to be in,” said Spencer. “I don’t know how that doesn’t extremely affect your psyche.” Still, “a lot of these kids really want it … They were born to do this. This is what they wanted desperately.”

Across the board, those who worked on Disney’s shows still express pride in what was created during the network’s heyday. “I can’t think of anyone I talked to who had regret or wished they hadn’t done their show,” said Spencer. “Many of them felt like their job working on a kids show was not just to make this content good, but it was also to provide a good experience for these kids who were growing up on set around them.”

And eventually outgrew the network, as did its core viewers. Disney High does not extend past 2010, when channel viewership began swiftly declining as kids’ attention shifted from cable to social media and short-form content online. The fickle magic of generational stardom at a foundational age moved elsewhere, even as the channel eventually relaxed some of its standards and practices and embraced openly queer characters. Even the current Disney-bred stars – Sabrina Carpenter, Olivia Rodrigo, Jenna Ortega, Dove Cameron – didn’t achieve their popularity on the channel; Disney served as training ground rather than a springboard.

“I don’t know that it will ever be replicated again,” said Spencer of Disney Channel’s once inescapable ubiquity. Even Disney’s attention has moved on from its own landmark channel; the book ends with a postscript in which Spencer visits an employee gift shop at corporate headquarters in Burbank, California, where not a trace of the channel could be found. Whether officially acknowledged or not, the legacy of the Disney Channel boom lives in the vast nostalgia for its programming – the idea of a Lizzie McGuire-esque animated character on your shoulder, the longstanding affection for newly minted Disney Legend Miley Cyrus, or the enduring appeal of High School Musical at karaoke.

When you watched Disney Channel, “you were still being molded as a person”, said Spencer. At that age, “you are figuring out who you are. So what you’re exposed to and what you connect with, that sticks with you for life.”