In 2010, Chicago Public Schools (CPS) was facing a dilemma--how to deliver a consistent sex education program in a complex and diverse school district. Four years earlier, the school board had adopted a policy calling for students in grades 5 through 12 to receive family life and comprehensive sex education. To help support schools in meeting this requirement, CPS purchased access to "HealthTeacher," a popular online K-12 health education program used by hundreds of other school districts around the country as a comprehensive and affordable approach to health education. In this study, the authors evaluate the impacts of a CPS demonstration project to support the implementation of "HealthTeacher" in a select number of Chicago 7th grade classrooms. The evaluation focuses on an enhanced version of "HealthTeacher's" main sex education module for middle school students. As a part of the demonstration, CPS provided teachers in study schools with supplemental training and technical assistance. District staff also monitored the delivery of program lessons through regular classroom observations and teacher feedback. The evaluation was thus designed to assess "HealthTeacher's" potential to meet the district's needs with some extra but sustainable level of program support. This report is divided into five chapters. Chapter I provides a detailed description of the "HealthTeacher" curriculum and briefly reviews prior research on the effectiveness of school-based sex education programs. Chapters II and III describe the study design, data and measures, and analytic methods. Chapter IV presents findings from the impact analysis, and Chapter V summarizes and discusses the implications of the results. The following are appended: (1) Consent and Retention Rates; (2) Data and Measures; and (3) Assessing the Sensitivity of Impact Estimates.