This paper discusses opportunities as well as constraints of evidence based policy and evidence based practice in education. Expectations held by different strands of the public (policy makers, teachers, parents) are discussed as constraint of the underlying educational research. Furthermore, such expectations constrain the communication between researchers and the public (a case of science communication). These relationships between educational research, evidence based policy and communication between research and the public are exemplified by case studies on three topics: The impact of violent computer games, the relationship between class size and students' learning outcomes and the issue of streaming in public schools.