In this article we describe research in which we used focus group data to study the implementation of preschool programs in elementary schools. 20 preschool teachers, 22 kindergarten teachers, and 53 parents from 10 schools in 5 states participated in the focus groups. These data, collected in the spring of 2001, were part of a 3-year multisite study of a comprehensive school reform program, the School of the 21st Century. Participants reported that implementation benefits included opportunities for preschool and elementary teachers to collaborate on and to coordinate curriculum and the needs of individual students, improved transitions to kindergarten for preschool students and their parents, and increased and sustained parent involvement. Reported implementation challenges included negotiating the use of classrooms, conflict in the sharing of resources such as the library and playground, building an understanding and respect for preschool education on the part of elementary school teachers, dealing with salary inequities between preschool and elementary teachers, and protecting preschool from the negative aspects of the accountability environment.