спасибо

Nearly 3,000 new schools have been launched since state legislatures began passing charter legislation in the 1990s. Chartering is a radical educational innovation that is moving states beyond reforming existing schools to creating something entirely new. Chartering is at the center of a growing movement to challenge traditional notions of what public education means.

Chartering allows schools to run independently of the traditional public school system and to tailor their programs to community needs. While not every new school is extraordinarily innovative and some school operations may mirror that of traditional public schools, policymakers, parents, and educators are looking at chartering as a way to increase educational choice and innovation within the public school system.

http://www.uscharterschools.org/pub/uscs_docs/index.htm

Я думаю, здесь charter в значении хартия.