Few educational problems have received more attention in recent years than the failure to ensure that elementary and secondary classrooms are staffed with qualified teachers. Severe teacher shortages, education researchers and policy makers have told us, are confronting our elementary and secondary schools. At the root of these problems, we are told, is a dramatic increase in the demand for new teachers resulting primarily from two converging demographic trends - increasing student enrollments and increasing teacher turnover due to a graying teaching force. Shortfalls of teachers, the argument continues, are forcing many school systems to resort to lowering standards to fill teaching openings, inevitably resulting in high levels of underqualified teachers and lower school performance.