Mayor Bloomberg's Department of Education (DOE) has focused its systemic school improvement efforts on one key strategy -- closing poorly performing high schools. The DOE has privileged school closure as its primary school improvement policy, as opposed to major initiatives to transform struggling schools from within. If this policy continues, more than 65,000 students - more students than the entire Boston public school system - will have had their high school experience marked by school closure. Because the DOE has a responsibility to ensure that those students do not become policy casualties, it must invest as much effort in ensuring a rich, rigorous, college-preparatory education for students in the final years of a closing high school as in developing and nurturing the new small schools they continue to create. This report examines what happened to students in the 21 schools that have completed their phase-out since 2000, when the DOE announced the first school closings, and predicts the destructive impact that school closings may have on students in the high schools that may be at risk of closing next.