In this first of a kind breakdown of data from over 26,000 U.S. middle and high schools, the authors estimate that well over two million students were suspended during the 2009-2010 academic year. This means that one out of every nine secondary school students was suspended at least once during that year. As other studies demonstrate, the vast majority of suspensions are for minor infractions of school rules, such as disrupting class, tardiness, and dress code violations, rather than for serious violent or criminal behavior. The authors are publishing this report because of the serious academic implications these statistics have for students who attend schools with high suspension rates. They believe greater awareness will help produce more effective approaches that create safe, healthy, and productive learning environments, which research indicates is best accomplished without resorting to frequent out-of-school suspensions. Done well, efforts to reduce suspensions should also improve graduation rates, achievement scores, and life outcomes, while also decreasing the rate of incarceration for juveniles and adults. The findings of this report also highlight critical civil rights concerns related to the high frequency of secondary school suspensions. They focus on secondary schools because children of color and students from other historically disadvantaged groups are far more likely than other students to be suspended out of school at this level. Appended are: (1) Data Omissions; (2) Methods and Treatment of Errors; and (3) School District Reports. Individual sections contain tables, figures and footnotes. [For "Out of School and Off Track: The Overuse of Suspensions in American Middle and High Schools. Executive Summary," see ED541731.]