Perspectives on Large scale Studies and students’ achievements in science (PELS) Anders Jakobsson, Eva Davidsson, Peter Allerup, Karl-Göran Karlsson, Helene Sørensen Introduction The background of this project is an interest in increasing the understanding of the outcomes of large international studies such as PISA and TIMSS. We want to explore possible trends concerning Swedish and Danish compulsory school students’ knowledge in and about science since the mid- 90s and, in addition, study these trends in relation to other studies within science education research. This means to conduct critical re- analyses, both quantitative and qualitative, of existing data in order to reveal trends within, for example, students’ achievements concerning conceptual knowledge or students’ contextual knowledge within different subject areas in science. These identified trends will be analysed and compared to relevant research to be able to gain a deeper and more thorough understanding about students’ knowledge in different knowledge domains related to science. The aim of the project is to explore similarities and differences, to analyse and describe Swedish and Danish trends and tendencies of students’ performances in large international studies such as PISA and TIMSS. This also includes  describing changes in students’ achievements during a longer period of time  relating the results to other research studies within science  to conduct qualitative analyses of existing quantitative data but possibly also to collect additional data. Research questions  What trends and tendencies are possible to discern when exploring large scale studies which aim to describe Swedish and Danish students’ knowledge about science, in a longitudinal perspective?  In what ways is it possible to assess the validity of these trends when applying qualitative analysis of quantitative data and in addition, compare these results to other studies within science education?  What factors, causes and explanatory models could facilitate the understanding of the possible trends when it comes to Swedish and Danish students’ knowledge about science, which are revealed in the analyses? Ongoing projects We have two parallel tracks running at the moment. A third will start in relation to a PhD-project.  CBAS When comparing the results of CBAS with PISA paper and pencil, there exist a large gender difference in all three participating countries. The aim of this study is to explore benefits and restrains about using computer-based assessment in science (CBAS) when investigating students’ science competencies. Furthermore, this study aims at investigating possible explanations to the large gender difference concerning students’ achievements on the CBAS test. Preliminary results suggest that the students needed to apply a wide range of competencies such as observing, modelling and reasoning in order to solve the problems. Furthermore, the CBAS test tended to contain gendered bias such as an overweight on physic related tasks and the acting people in the movies were only boys, often “playing around”.  Longitudinal trends in PISA In this part we have chosen to analyse the results from PISA and TIMSS items that are represented in several separate meassurements. Our expectation is that this analysis will increase our possibilities to draw valid conclusions about longitudinal trends on a national level and to conclude what these trend consist of.  Doctoral project This part of the project aims to explore how individual students, as well as groups of students, work with selected PISA items with or without different kinds of means such as computers, databases, and other sorces.