Contemporary educational thought holds that one of the pivotal causes of inadequate student achievement is the inability of schools to staff classrooms with qualified teachers. The primary sources of the problem of underqualified teachers are, most assume, deficits in the quantity of prospective teachers recruited and in the quality of preparation prospective teachers receive. In this study, I hypothesize that the manner in which schools are organized and in which teachers are utilized can account for as much of the problem of underqualified teaching as do inadequacies in the supply or training of teachers. This analysis specifically focuses on a little recognized source of underqualified teaching--the problem of out-of-field teaching; that is, teachers being assigned by school administrators to teach subjects that do not match their training or education. I use data from the Schools and Staffing Survey, a large, comprehensive, nationally representative survey of teachers conducted by the National Center for Education Statistics. The results of the analysis show that, while most teachers hold basic qualifications, a significant proportion of these qualified teachers are assigned to teach classes out of their fields. The data also show that out-of-field teaching is not primarily due to school hiring difficulties resulting from teacher shortages, as is commonly believed. In contrast, the analysis shows that a number of aspects of the administration and organization of schools are significantly related to out-of-field teaching. For example, school district regulations concerning minimal education requirements for new hires, the quality of principal leadership, the strategies that schools use to cope with teacher recruitment and hiring, and average school class sizes all have an independent association with the extent of out-of-field teaching in schools, after controlling for other factors. (Contains 2 figures, 4 tables and 40 notes.)