For some time educational policy analysts have been predicting that shortfalls of teachers resulting primarily from increases in student enrollment and teacher retirements will make it very difficult for schools to find qualified teachers and, in turn, will hurt school performance. Moreover, analysts have argued that shortages will be worse for particular fields, such as math and science, because of difficulties in recruiting qualified candidates. This paper summarizes what the best available nationally representative data reveal about the rates of, and reasons for, teacher turnover for both math/science and other teachers. The data show that, contrary to conventional wisdom, the problems schools have adequately staffing classrooms with qualified teachers are not primarily due to teacher shortfalls, stemming from either increases in student enrollment or increases in teacher retirement. Rather, the data show that school staffing difficulties are primarily a result of a "revolving door" where large numbers of teachers depart teaching for other reasons, such as job dissatisfaction and in order to pursue better jobs or other careers. These findings have important implications for educational policy. Teacher recruitment programs - the dominant policy approach to addressing school staffing inadequacies - will not solve the staffing problems of schools, if they do not also address the problem of teacher retention. In short, the data indicate that recruiting more teachers will not solve teacher shortages if large numbers of such teachers then prematurely leave.