Analyses of the impact of reform-based teaching practices in Florida International University's program have been previously reported. However, the impact of the field experiences "per se" has not been assessed. Using a cross-case analysis approach, the authors assess the impact of voluntary field experiences with teachers who practice innovative mathematics methods in keeping with school reform mandates on the actual teaching behaviors and beliefs of mathematics teacher candidates. One can infer that the optional supplementary experiences, especially the PAC (Partnership in Academic Communities) experience, either enhanced or reinforced a positive impact on the development of reform-centered and standards-based preservice teacher practitioners. The pre-service teachers who had many more supplemental experiences performed significantly better in constructing standards-based, reform oriented classrooms than those who had fewer such experiences. (Contains 2 tables and 3 notes.)