Professional Development Schools (PDS) have become a widely used vehicle for the educational and professional development of both preservice and in-service teachers. Three key stakeholders are generally identified in the research about PDS--preservice teachers, experienced teachers, and K-12 students. The purpose of this research was to examine the impact of preservice teachers on the students in their assigned practicum classrooms. An experimental design was used to study the student achievement outcomes in classrooms with student teachers compared with classrooms in which no student teachers were present that year. The importance of this research is underlined by Fry and Konopak's (2002) call to action, saying that "while those involved in teacher education have made great strides in developing a coherent and defined knowledge base, there I still much work to be done." (Contains 1 table.)