The failure to ensure that the nation's classrooms are all staffed with qualified teachers is one of the most important problems in contemporary American education. Over the past decade, many panels, commissions, and studies have focused attention on this problem and, in turn, numerous reforms have been initiated to upgrade the quality and quantity of the teaching force. This report focuses on the problem of underqualified teachers in the core academic fields at the 7-12th grade level. Using data from the nationally representative Schools and Staffing Survey, conducted by the National Center for Education Statistics, this analysis examined how many classes are not staffed by minimally qualified teachers, and to what extent these levels have changed in recent years. The data show that while almost all teachers hold at least basic qualifications, there are high levels of out-of-field teaching--teachers assigned to teach subjects that do not match their training or education. Moreover, the data show that out-of-field teaching has gotten slightly worse in recent years, despite a plethora of reforms targeted to improving teacher quality. The report discusses possible reasons for the failure of these reform efforts. My thesis is that, despite the unprecedented interest in and awareness of this problem, there remains little understanding of a key issue--the reasons for the prevalence of underqualified teaching in American schools--resulting thus far in a failure of teacher policy and reform. I conclude by drawing out the lessons and implications of these failures for the prospects of the No Child Left Behind Act to successfully address the problem of underqualified teachers in classrooms in the coming years. (Contains 1 chart, 2 tables and 4 figures.)