The subtext [of the concept of 'miracle schools'] is that poverty and resources are not actually problems for urban schools; if they could just test more often and fire more teachers, the corporate reformers imply, then test scores would soar. This analysis suggests that schools enrolling the neediest students do not need more resources, and it rationalizes the current trend of draconian budget cuts for public education.
Apparently there is a blog evaluating the claims of miracle schools and finding that really they aren't.
Americans like the idea of "miracle schools" for the same reason that we like movies about the underdog baseball team winning or the guy in the mail room running the company. Probably not unrelated is how appealing Americans find the concept of achievement without hard work. In reality, resources matter. Giving too much credence to the ideas of miracle schools because we like the narrative could end up depriving >99% of disadvantaged children of the chance to learn and advance, just because we like the narrative of the <1% who succeed despite the bad odds. And it's way cheaper in the short run, even if more expensive in the long run.