Demand for special education teachers grew continuously from the passage of Public Law 94-142 in 1975 through 2005, when this trend reversed. From 2005 to 2012, the number of special education teachers employed by U.S. schools declined by >17%. The primary purpose of this investigation was to determine factors that contributed to this decline. We parsed change in number of special education teachers employed into four constituent elements and found that these recent reductions were fueled by decreases in disability prevalence and the relative ratio of teachers to students in special versus general education, which favored the latter. These changes have important implications for teacher preparation programs' efforts to adequately prepare special and general educators and for policies designed to improve teacher quality.