Eigth-grade teacher Taylor Johnson talks recently with students Jamia Stewart, from left, Belen Ibarra, Rajae Anderson and Marilyn Besler at Paz Elementary school in Chicago. Paz is the lowest performing school in the United Neighborhood Organization charter network. (Antonio Perez, Chicago Tribune / November 29, 2011)

If the past decade was defined by a remarkable expansion of charter schools in Chicago, the next 10 years might ultimately be about accountability.

The state last week released detailed performance data for city charter schools for the first time, revealing that many schools from even the most prominent charter networks struggle to close the achievement gap for low-income students.

In that respect, charters are no different from the traditional neighborhood schools they're often measured against. But the timing of the state's report was interesting, considering the next day, Chicago Public Schools officials announced they are seeking to close two