This article argues that school social capital is crucial for school effectiveness, but it has been disregarded in the traditional school administrative theory. Therefore, this article tries to illustrate the significance of school social capital to school effectiveness. School social capital is defined as the social resources embedded in internal and external school social networks. According to the existing literature, if schools possess more socially embedded resources, the overall school performance will be better. Thus, managing school social capital is important for school to strive for effectiveness. It is suggested that schools can manage school social capital through (a) maintaining the possessed social resources by expressive action and cultural intervention, and (b) acquiring additional social resources by instrumental action and the balance of loosely coupled system and tightly coupled system of school social networks. However, there is no specific theory explaining school social capital and its relationship to school effectiveness. Therefore, it will be contributive to the development of a theory of school social capital. (Contains 1 figure.)