International comparative studies of educational achievement usually have multiple purposes and may have impact on educational policy and practice in various ways (see e.g. Plomp, Howie, & McGaw, 2003).

First, the ‘mirror’ function – descriptive comparisons with other countries might serve to identify particular aspects of a national system that could be considered problematic because they are out of line with what is found in other countries (e.g., the content of a curriculum, achievement levels of target persons). A second function is monitoring, which involves the assessment of educational processes on different levels in the education system with the purpose of making informed decisions about change when and where it is needed. A cycle of regular assessments in target domains that are being monitored to provide trend data is needed to do this. Organizations conducting international comparative studies of educational achievement such as the IEA and the OECD value this function and are committed to cyclical study designs. Third, findings from these studies can contribute to our understanding of differences between or within education systems, which should be helpful in making decisions about the organization of formal learning environments (for instance schools), the deployment of resources, and the practice of teaching. Fourth, variation between educational systems revealed in international comparative studies can be taken as a starting point for research ("the world as a laboratory"), leading to a better understanding of the factors that contribute to the effectiveness of education. Finally, international comparative achievement studies also serve to promote general 'enlightenment'. In this case there is not a direct link to decisions, but rather a gradual diffusion of ideas into the sphere of organizational decision making. In this view, the findings of international studies may contribute to clarifying policy makers' assumptions about what learning environments try to achieve, what they actually achieve, and what is possible to achieve, as well as to enriching public discussion about education.

For this symposium we have invited national research coordinators and national project managers from international comparative achievement studies as well as colleagues working on in-depth secondary analyses in this field to prepare contributions to be included in thematic sessions for which we suggest as umbrella theme: Towards explaining achievement: inferring cause and effect in the context of cross-sectional surveys and in particular the challenges inherent in drawing conclusions, given the complexity of educational systems and teaching/learning environments.

The six papers to be presented in this symposium have been organized in two thematic sessions. This is the proposal for the first session.

Plomp, T., Howie, S.J., & McGaw, B. (2003). International Studies of Educational achievements. In D. Stufflebeam & T. Kellaghan (Eds.), International Handbook on Educational Evaluation (pp. 951-978). Dordrecht, the Netherlands: Kluwer Academic Publishers.