This paper examines how relationships among government and "outside" organizations influenced policy implementation of new dropout prediction data systems. Using comparative historical and network analyses of three cities, I suggest the concept of interorganizational coupling--highlighting how the dependence and (in)formal collaborations among local school improvement organizations affected implementation speed, variation, and constraint. In Chicago, the loosely coupled system influenced slow and varied implementation, sustained by interpersonal relations and challenged by unclear division of labor. In Philadelphia, the tightly coupled system shaped swift and uniform changes, constrained by questions of sustainability. In New York, the tightening system led to fast yet variable transformations, limited by competition among organizations. Broadly, the article contributes to studies of education policies, interorganizational networks, and school improvement.