This paper argues that education should become more evidence-based. The distinction is made between using existing research and establishing high-quality educational research. The need for highquality systematic reviews and appraisals of educational research is clear. Evidence-based education is not a panacea, but is a set of principles and practices for enhancing educational policy and practice.

We provide a 'how to' guide to undertake systematic reviews of effects in international development, by which we mean, synthesis of literature relating to the effectiveness of particular development interventions. Our remit includes determining the review's questions and scope, literature search, critical appraisal, methods of synthesis including meta-analysis, and assessing the extent to which generalisable conclusions can be drawn using a theory-based approach. Our work draws on the experiences of the International Initiative for Impact Evaluation's (3ie's) systematic reviews programme.

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The Campbell Collaboration (C2) was founded on the principle that systematic reviews on the effects of interventions will inform and help improve policy and services. C2 offers editorial and methodological support to review authors throughout the process of producing a systematic review. A number of C2's editors, librarians, methodologists and external peerreviewers contribute. The Campbell Collaboration

This paper argues that educational policy and practice has much to gain from systematic reviews and other methods of research synthesis. Different types of reviews are considered, including narrative reviews, vote-counting reviews, meta-analyses, best evidence synthesis, and meta-ethnography. It is argued that systematic reviews allow researchers, and users of research, to go beyond the limitations of single studies and to discover the consistencies and variability in seemingly similar studies. This, in turn, allows for some degree of cumulative knowledge of educational research that is often missing in the absence of systematic reviews. Some limitations of systematic reviews and research synthesis for educational policy and practice are also discussed. The work of the Campbell Collaboration as an international organisation that promotes the use of systematic reviews in educational policy and practice is outlined.