This paper examines the impact of pre-service preparation and in-service formal and informal training on the ability of teachers to promote academic achievement among students with disabilities. Using student-level longitudinal data from Florida over a five-year span the authors estimate "value-added" models of student achievement. There is little support for the efficacy of in-service professional development courses focusing on special education. However, teachers with advanced degrees are more effective in boosting the math achievement of students with disabilities than are those with only a baccalaureate degree. Also pre-service preparation in special education has statistically significant and quantitatively substantial effects on the ability of teachers of special education courses to promote gains in achievement for students with disabilities, especially in reading.