Charter schools gained traction in the 1990s with parents, teachers and other community members who were frustrated with public-school offerings and wanted an alternative. Such schools secure a "charter"—or a contract with the state or local government—detailing how the school will be run. The schools, which are part of the public school system, are run autonomously by community groups. In exchange, they must show more accountability than average public schools in order for their charters to be renewed—which is usually every five years.
The data on whether charters are working are mixed, at best. A Stanford University analysis … is widely considered one of the most comprehensive studies …. It found that only 17% of charter schools reported academic gains that were significantly better than traditional public schools, 37% of charter schools showed results that were worse than traditional public-school counterparts, and 46% of charter schools demonstrated no significant difference.
Source: here