The Chicago High School Redesign Initiative (CHSRI), a partnership between the Chicago Public Schools (CPS), the Bill and Melinda Gates Foundation, and local foundations, opened 23 small high schools between 2002 and 2007 designed to address high dropout rates and low academic performance. Using CPS administrative records, test score data and responses from a bi-annual survey of all CPS teachers and students, we compare school environments and student outcomes in small high schools to other CPS high schools. Our research on this initiative mirrors most findings from other researchers looking into similar initiatives across the country:  Small high schools foster more personal and supportive contexts for both teachers and students and have a beneficial effect on attendance and graduation rates. Although in Chicago, the graduation benefits were strongest for the most at-risk students, there was no evidence that CHSRI schools improved student achievement test scores or led to different instructional practices.

 Yet we found substantial variation across CHRSI schools in terms of school climate, instructional reform activity and student outcomes. Using qualitative and quantitative indicators across a sample of ten schools, we investigate the characteristics of the most successful CHSRI schools. We identify three conditions found in schools with comparatively high student achievement -- strong teacher professional communities, deep principal leadership, and extensive teacher influence. The findings highlight that how adults work together in small schools is a crucial factor in raising student achievement. In particular, it suggests that collective work on improving instruction is a key lever for raising achievement.  The findings also point to the benefits of balancing the direction and initiative provided by principals with teacher voice and leadership.  Because we know that reducing school size does not automatically lead to such developments, schools will need to intentionally focus on creating these key characteristics.