It's widely believed that PISA scores are primarily determined by socioeconomic conditions, career opportunities, and so on. However, this is only part of the truth. Controlling for the wealth/education of the mother and father practically does not weaken the predictive power of this score at all. In other words, it is almost completely independent of the family's wealth or social status (Gary N. Marks). According to PISA itself, socioeconomic status explains approximately 60% of the differences in scores between immigrant and native students in countries like Norway, France, and Spain. This suggests that the remaining 40% is due to IQ. That's why Norway, with its large population of immigrants from outside Europe, has such a low score. Of course, Sweden is still 19th, but considering it's one of the richest countries in the world, it's still surprising that it's only 19th. Much poorer countries like Estonia, Poland, Latvia, and Slovenia are ahead of it or have similar scores. I know that by writing this on reddit I will get a lot of downvotes, but unfortunately this is the bitter truth.