The University of Chicago Consortium on Chicago School Research and the American Institutes for Research (AIR) partnered to examine five different models initiated by the Chicago Public Schools (CPS) in 36 schools. CPS was an early adopter of dramatic intervention strategies in low-performing schools, and the reforms in this study were implemented between 1997 and 2010. All of the schools were identified as chronically low performing and were reformed in ways consistent with the elements described in the school improvement models recommended by the federal government. The goals of the study were to make clear how school reform occurred in Chicago--showing the actual changes in the student population and teacher workforce at the schools--and to learn whether these efforts had a positive effect on student learning overall. Since 1997, CPS has initiated five distinct reforms that aim to dramatically improve low-performing schools in a short time. These initiatives are Reconstitution (seven high schools), School Closure and Restart (six elementary schools and two high schools), placement into the School Turnaround Specialist Program (STSP) model (four elementary schools), placement into the Academy for Urban School Leadership (AUSL) model (ten elementary schools and two high schools), and placement into the CPS Office of School Improvement (OSI) model (two elementary schools and three high schools). Main findings from the study include: (1) Elementary/middle schools that went through reform made significant improvements in test scores compared with similar schools that did not; however, large improvements did not occur immediately in the first year; (2) High schools that underwent reform did not show significant improvements in absences or ninth grade on-track-to-graduate rates over matched comparison schools, but recent high school efforts look more promising than earlier ones; (3) Schools that underwent reform generally served the same students as before intervention, with the exception of one model of reform; (4) Schools under the Closure and Restart model experienced substantial changes to their student body composition; (5) The vast majority of teachers in schools under Closure and Restart, AUSL and OSI models were not rehired after reform; and (6) The teacher workforce after intervention across all models was more likely to be white, younger, and less experienced, and was more likely to have provisional certification than the teachers who were at those schools before the intervention. School-by-School Changes in Student Achievement are appended. (Contains 1 table, 9 figures and 6 endnotes.)