Charter schools are based on exploiting the lovely free market doctrine of externalities, in other words, getting someone else to pay for the losses. In school terms, this means the expensive kids are non starters in the charter school world: special ed, special needs, language learners, the less intelligent, behavioral problems and the like. Kids that require extra psychologists, intervention teachers, SPED and ELL teachers.
Charter schools are just a new segregation, not based on race and poverty explicitly, although this manifests itself in the statistics as well. Through location, stringent rules, the ability to kick out who they want, and targeted marketing, they are excluding the kids who cost too much. They dump the expensive kids back on the public schools as an externality.
Capitalist principles are based on money profit, they are not based on meeting the social needs for everyone. Of course they will fail at educating everyone but that's the point. Bring up a few kids from the working classes to provide a veneer of meritocracy and crush everyone else at the same time. More child labor, more job specific skills with less on citizenry and understanding society.
