A curriculum initiative project was implemented in four schools in Singapore over a span of five to six weeks during 2004. The project employed a number of different schools: girls only, boys only and co-educational schools; different levels of performance in a graded situation; multiple teachers and classes within each site; and control and experimental conditions for the curriculum implementation. In conducting research in the diverse schools, there was also an opportunity to study the interactions between action research and multiple site case studies. Though action research and case studies are frequently used in education to research curriculum initiatives, their interactions are seldom explored. Moreover, the practical benefits and challenges of multiple site case studies in action research are little discussed. In this paper, the interactions between action research and multiple site case studies as well as the practical and theoretical benefits and challenges are explored. By examining the particular benefits and challenges presented by this project, it is hoped that this paper will contribute to a better understanding of multiple site case study action research through describing the practical benefits and challenges, as well as the theoretical advantages and disadvantages, of multiple site action research case studies, and the means used to overcome the challenges that arose during the course of the case studies. (Contains 1 table and 1 figure.)