Our nation is squandering one of its most important resources--our best teachers--and children are paying the price. We asked a simple question: "Will our nation's bold efforts to recruit more top teachers and remove the least effective teachers put a great teacher in every classroom?" We ran the numbers and discovered a disappointing answer: No. Even if these reforms were wildly successful, nearly two-thirds of classrooms still would not have great teachers. Why does this matter? Only great teachers--those in the top quartile--achieve the student learning progress needed to close our nation's achievement gaps and raise our bar to internationally competitive levels. Others do not. But approximately 64,000 top teachers leave teaching every year. And the best teachers who stay reach no more children than the very worst teachers. If we add high-performer retention and reach extension to bold recruiting and dismissal, 87 percent of classes could be taught by gap-closing, bar-raising teachers--in a mere half-decade. This outcome is within our reach--but only if we vastly expand opportunities for great teachers by: Building an Opportunity Culture for America's Teachers. Written with support from The Joyce Foundation, this report explores the potential impact of policy initiatives designed to improve student access to great teachers. Current policy initiatives overlook the most obvious, immediate source of improved teaching effectiveness: the great teachers we already have. The top 25 percent of U.S. teachers--more than 800,000 of them--already achieve results that would enable all of our children to meet and exceed standards. (Contains 14 figures and 72 notes.) [For related reports, see "Opportunity at the Top: How America's Best Teachers Could Close the Gaps, Raise the Bar, and Keep Our Nation Great. Summary" (ED539988) and "Opportunity at the Top: How America's Best Teachers Could Close the Gaps, Raise the Bar, and Keep Our Nation Great. Executive Summary" (ED539999).]