The failure to ensure that all of the nation's classrooms are staffed with qualified teachers is one of the most widely discussed, but least understood, problems facing elementary and secondary schools. In recent years, dozens of reports and reform initiatives have sought to solve this problem. Unfortunately, the array of recent efforts do not address some of its key causes. One of the least recognized of these unaddressed causes is the phenomenon known as out-of-field teaching--teachers assigned to teach subjects for which they have little preparation, education, or background. This practice makes even highly qualified teachers highly unqualified if, once on the job, they are assigned to teach subjects for which they have little background or preparation. This seemingly odd and irrational practice has been largely unknown to the public and to policy makers. One of the reasons the problem has been so little noted was an absence of accurate data. However, in the early 1990s, the release of the Schools and Staffing Survey (SASS)--a major new survey of the nation's elementary and secondary teachers conducted by the U.S. Department of Education--remedied this situation. In this article, the author offers a cautionary tale of his own exploration of this troubling problem in education. He found that simply gathering and analyzing data will not solve entrenched problems in education policy; some rethinking on the part of policy makers is also necessary. (Contains 2 notes.)