In the context of the current financial crisis, Public-Private Partnerships (PPPs) have acquired iconic status in the discussions on education reform in both industrialized and developing countries. PPPs, and the associated market rules they introduce, can provoke important equity and accountability problems in education systems. This paper reflects on the shortcomings of PPP programmes in education and on the methodological challenges to analyze them in a rigorous way. Our methodological proposal is grounded on the realist evaluation approach (Pawson). This means, first, any evaluation of PPP programmes needs to start by identifying the generative mechanisms that are being activated by the programme in question (which means that if we want to understand the outcomes of PPPs we first need to understand PPPs). Second, PPPs, as any other education intervention, are embedded in social systems and work selectively. This means that the results of PPPs are very sensitive to the way programmes have been designed, as well as to the strategies, behavior and actions of the subjects that are part of the programme. Based in a realist evaluation approach, the paper will show how specific PPPs programmes do not have the expected effects as defined by education planners and market advocates.