Discussions of teacher turnover usually focus on "how many" teachers leave schools each year, without regard for their performance in the classroom. This oversimplification masks the real teacher retention crisis: not only a failure to retain enough teachers, but a failure to retain the "right" teachers. This executive summary presents findings of a study that examined the real retention crisis through the experiences of a group called the "Irreplaceables": teachers who are so successful that they are nearly impossible to replace. Teachers of this caliber provide more engaging learning experiences for students and help them achieve five to six more months of learning each year than students of low-performing teachers--academic results that can be life-changing. (Contains 5 figures.) [For the main report, "The Irreplaceables: Understanding the Real Retention Crisis in America's Urban Schools," see ED533959. For related report, "5 Ways Principals Can Keep More Irreplaceable Teachers. The Irreplaceables: Understanding the Real Retention Crisis in America's Urban Schools," see ED533961.]