Recent literature on Professional Development Schools (PDSs) emphasizes outcomes, accountability, and sustainability. This paper addresses themes that influence PDS sustainability, describing the University of South Florida's (USF) examination of three PDS sites, which led to questioning of the impact of leadership transitions on PDS sustainability. Themes of sustainability include the evasive nature of PDS outcomes, collaboration levels, compatible views of pedagogy, staffing considerations, governance structures, reward systems, essential fiscal infrastructures, the role and nature of inquiry, change in teacher education policy/practice, and time considerations. USF developed a nondirectional approach to examining its PDS sites. The three sites discussed here have moved into threshold conditions defined by the National Council for Accreditation of Teacher Education draft standards for PDSs. Focus group interviews with key stakeholders indicated that the standards were an excellent yardstick for documenting the evolution of the PDSs and determining areas needing further development. Data analysis examined: PDS practices that reflected the draft standards, that reflected the draft standards but did not emerge in the data, that were encouraged by the draft standards but were absent from the PDS model, and that were present in the PDS model but absent or vague in the draft standards. Researchers created a visual representation of the data to illustrate significant changes in leadership at the three sites, identifying 16 major transitions over 8 years. The paper summarizes self-reflection from administrators at each site. The survey instrument is included. (Contains 44 references.) (SM)