Every three years, the OECD-run Programme for International Student Assessment - or Pisa - publishes results of test that several hundred thousand 15-year-olds around the world have taken in reading, maths and science. And the test scores tend to attract a lot of attention. Not least in Sweden, which has had its share of so called "PISA-shock" and "PISA-crisis".
But scientists have over the years criticised the test and the attention it gets. One of them is Norwegian Svein Sjøberg, a professor emeritus in science education at Oslo University, who says the OECD - the Organisation for Economic Co-operation and Development - has hijacked the way we look at pupils, schools and education.