Given the challenges facing American public education today, identifying effective teachers is a more vital task than ever before. In the U.S. public school system today, the method used to determine teacher effectiveness--and thus to drive salary, promotion, and tenure decisions--is based on a few external credentials: certification, advanced degrees, and years of experience in the classroom. Yet according to a new analysis of student performance in Florida that two colleagues and the author conducted, little to no relationship exists between these credentials and the gains that a teacher's students make on standardized math and reading exams. The expansive study included all test-taking public elementary school students in the state of Florida over a period of four years. This study, to be published in the peer-reviewed journal "Economics of Education Review," builds on two decades of research from a variety of school systems and confirms a consistent finding: external teacher credentials tell next to nothing about how well a teacher will perform in the classroom. Along with coauthors Jay Greene and Bruce Dixon (professors at the University of Arkansas), the author of this Issue Brief utilized a data set provided by the Florida Department of Education to study the relationship between elementary school teachers' training and experience, on the one hand, and the learning gains made by their students in a given year, on the other. (Contains 10 endnotes.)