Nima Sanandaji, via a kind reader:

Swedish fourth graders are leading the world in mathematics, followed closely by those in other developed European nations, at least if we look at students’ reported self-confidence in the subject. Fully 77% of Swedish students at fourth grade express a high level of confidence about their learning, compared to merely 5% who express a low level. In Austria, Germany, Denmark, and Norway seven out of ten students have high confidence about their mathematics knowledge. One in ten or fewer have low confidence. Self-confidence is somewhat less common amongst US fourth graders, where 67% believe that they perform highly in mathematics and 10% express the opposite view. Unfortunately, this confidence – in America and elsewhere – is not backed up by high achievement.
As shown by the Trends in International Mathematics and Science Study, the average US student with high confidence only scored 551 on the test. This is just half a standard deviation from the average score of 500. The phenomenon where many students believe that they are doing well in mathematics – while they are in fact lagging behind other nations – is even more evident in several European nations. In Sweden the average score of the self-identified high achievers is only 514. The sureness of Swedish students seems to rise from a progressive school system. As more focus is put on promoting self-expression and raising self-esteem than on actual knowledge gathering and hard work, students with only slightly higher international scores identify themselves as being high achievers.

Related: www.wisconsin2.org