Charter schools as private investment vehicle

This is an article about the appalling trend of charter schools' serving as equity vehicles for private investors.  The most relevant passages of the article for me:

"Too bad the kids in charter schools don’t learn any better than those in plain-vanilla public schools. Stanford University crunched test data from 26 states... Nor does the evidence show that charters spend taxpayers’ money more efficiently... About the only thing charters do well is limit the influence of teachers’ unions. And fatten their investors’ portfolios."