There is nothing that the government does that cannot be done better and more efficiently by the private sector. That is all a charter school is a privately managed school that costs less and teaches the children more. Because the staff is held to a higher standard we get better results from the private sector than we do from the government.
The privatization of schools remove the focus of schooling from education to profit. Rather than promoting better teachers, the school is given incentives to find the cheapest teachers possible that are still somewhat effective in order to improve their profit margin. This decreased pay would eventually lead to a decreased quality in education because the brightest and the best will choose better paying occupations.