The main reason is that girls' school results have deteriorated. The pattern is visible from grade 6 to upper secondary school.
"It shows that the development cannot be explained by changes in a particular age group, but that it is a more profound trend", says Sanna Vent, education councilor at the National Agency for Education, in a press release.
In grade 9, the difference between girls' and boys' school results has never been as small as now, notes the National Agency for Education.
Girls' school results have decreased the most in the subject of mathematics, the report also shows.
"There are clear differences between the sexes when it comes to the attitude towards mathematics. Girls are less positive than boys about learning mathematics and have poorer self-confidence in the subject", says Sanna Vent.
It is mainly girls with a Swedish background who have worsened their school results, and this applies regardless of socio-economic background.
There is no straightforward explanation for the trend, but previous studies have shown that girls are increasingly dissatisfied with school and feel increased stress. There are also differences when it comes to access to special support, according to the National Agency for Education.
