The success of Disney Channel was kind of an accident. The halcyon days of the mid-2000s ushered in “High School Musical,” and the reach of “Hannah Montana” permeated pop culture beyond the tween audience it targeted. But before that, the Disney Channel was bumbling along since its launch in 1983, mostly broadcasting kids cartoons that harked back to the company’s animation renaissance in the early 1990s.

It wasn’t until “Lizzie McGuire,” which starred Hilary Duff in the title role, that network executives realized what they had on their hands. “Hilary and Lizzie were really what changed and shaped what came later with Miley and Selena and Demi,” says Ashley Spencer, author of “Disney High: The Untold Story of the Rise and Fall of Disney Channel’s Tween Empire” — out now. Duff’s star power was undeniable, and the slightly aged-up — at least from the Saturday morning cartoon crowd — tween “Lizzie McGuire” audience hung on her every word.

But, as Spencer contends in “Disney High,” it was a challenge to mobilize all the disparate Disney departments to capitalize on the show and Duff’s appeal. Though the channel paid the price for not signing the stars of “The All New Mickey Mouse Club,” including Britney Spears, Justin Timberlake and Christina Aguilera, to Disney record contracts while they were still on the show, Spencer writes, “they weren’t thinking like that. Yet.

” “Once the Disney record labels started cooperating with.