For most of the past decade, the Chicago Public Schools (CPS) have received significant support from the Bill and Melinda Gates Foundation (BMGF) to improve the performance of city high schools. As part of that support, the Foundation contracted with SRI International and the Consortium for Chicago School Research to conduct a comprehensive evaluation of high school reform in Chicago. A major part of those reform measures, the Instructional Development System (IDS), is addressed in this report. The investigation into IDS was initially designed to follow the initiative for 4 years, but the BMGF decided to redirect its resources and end the evaluation after the first round of data collection. This report, therefore, sets forth preliminary evaluative work concerning the implementation and early outcomes of the IDS initiative. Using data collected from school visits in fall 2008 and administrative data, we describe the successes and challenges associated with implementing the IDS initiative, indicate what instruction looked like in the first two waves of IDS schools, and examine early evidence of the initiative’s impact on student performance.