You're making an assumption that itself needs to be evaluated. My city (Albany, NY) was selected as an early experiment in Charter Schools in the state, as it's the state capital, and the public schools have a bad reputation.

In the media, the message is always about quality of education and high standards -- because the audience is the political class who funds the schools. But the outreach to parents (found in bus shelters, pamphlets, hip hop radio, etc) is a message that usually is around childcare and uniforms. Longer school hours + longer school year == less daycare expenses and arrangements.

In terms of outcomes, it's all over the map. Several charters have closed for poor performance, and some do well.