Collaboration between schools has come to be regarded as an important way in which they may find the means to improve their educational performance. Yet little is known definitively about what impact this has for improving pupil attainment. In this literature review, by CMRE Executive Director James Croft, finds that despite the popular rhetoric about the importance of school collaboration, the majority of analysis is qualitative and focuses on staff development and support, rather than pupils' outcomes. In terms of quantifiable impacts for students, we know very little. This report explores the theoretical confusion around the purpose of school collaboration and common methodological problems with much research undertaken in the field. It draws a key distinction between collaboration effects, and chain and federation effects, arguing that the latter suggests that corporatisation may be more important than collaboration for school improvement. Sustainable growth of corporate structures, and more tightly focused and managed school partnerships, are only likely to emerge however, through greater attention to competitive incentives in the schools market.