1. 1Faculty of Mathematics and Natural Sciences, University of Groningen, Groningen, The Netherlands
2. 2Department of Science Teaching, Weizmann Institute of Science, Rehovot 7610001, Israel
3. 3Faculty of Education, Bogazici University, Istanbul, Turkey
4. 4Institute of Education, University of Lisboa, Liboa, Portugal
5. 5IPN, Institute for Science and Mathematics Education, Kiel University, Kiel, Germany
6. 6Department of Phyiscs, Helsinki University, Helsinki, Finland