Although the educational community has learned much about better educational practices, less is known about processes for implementing new practices. The standard model of diffusion suggests that people change perceptions about the value of an innovation through communication, and these perceptions then drive implementation. But implementation can be affected by more instrumental forces. In particular, members of a school share the common fate of the organization and affiliate with the common social system of the organization. Thus, they are more able to gain access to each others' expertise informally and are more likely to respond to social pressure to implement an innovation, regardless of their own perceptions of the value of the innovation. This article characterizes informal access to expertise and responses to social pressure as manifestations of social capital. Using longitudinal and network data in a study of the implementation of computer technology in six schools, the authors found that the effects of perceived social pressure and access to expertise through help and talk were at least as important as the effects of traditional constructs. By implication, change agents should attend to local social capital processes that are related to the implementation of educational innovations or reforms.