The failure to ensure that all classrooms are staffed with qualified teachers is one of the most important problems in U.S. education. Dozens of reports and national commissions during the past decade have focused on this issue, and numerous initiatives have attempted to upgrade the quality and quantity of the teaching force. Reformers in many states have pushed tougher teacher-certification standards and more rigorous academic requirements for teaching candidates. A range of programs to recruit new candidates into teaching have sprung up, including programs for midcareer professionals, alternative certification programs, and Teach for America–like programs to lure the "best and brightest" into understaffed schools.

Although these are all worthwhile reforms, such efforts alone will not solve the problem of underqualified teachers because they do not address some of the key causes. One of the least recognized causes is out-of-field teaching—when teachers are assigned to teach subjects that do not match their training or education. Highly qualified teachers may actually become highly unqualified if they are assigned to teach subjects for which they have little training or education.