Forbes has an interview with Judy Taylor who is the person responsible for finding talent at Disney.

Talking about Demi, Judy tells Forbes.com:

In the fall of 2006, I believe, she showed up on a Dallas tape that our casting directors had made. We probably identified half a dozen kids on that search to watch out for or have on the radar, and she was one of them. Then, when we started assembling As the Bell Rings, and it turned out we were going to shoot it in Texas, we figured it would be a great incubator. It's a short interstitial piece, which made it a great place to maybe launch somebody or give them some real technical experience and see how they deliver.

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