Professional-development schools are collaborations between universities and public schools to improve the nation's teaching force. Prospective teachers are assigned to K-12 schools for formal instruction, planned experiences in classrooms, and mentoring from master teachers. This paper presents findings of a qualitative study that described the role of the principal in the professional-development school (PDS) in seven elementary schools participating in the Texas Centers for Professional Development and Technology. Data were gathered through site visits conducted in 1994-95, a review of documents, and interviews with key participants in the schools. Findings indicate that the configuration, size, complexity, and staffing of the school had a significant effect on the PDS roles, and consequently, on the probability of institutionalization of the PDS model at the school. The study applied the Miles and Huberman (Miles 1983) model of institutionalization to predict which of the schools would institutionalize the PDS and which would abandon it as external funding was reduced. The paper also offers recommendations for increasing the probability of successful implementation and institutionalization: (1) Provide staff support for principals in schools with large numbers of interns and other students; (2) develop job descriptions and expectations for principals; (3) provide orientation and staff development; (4) offer training in other related areas, such as conflict resolution and communication skills; and (5) provide additional funds for educational technology and communication linkages. Five tables are included. (LMI)