Findings of the Trends in International Mathematics and Science Study, TIMSS, which examined students around the world between the years of 2011 to 2015, appear to confirm earlier observations of a decline in test scores by PISA, the Programme for International Student Assessment.
According to TIMSS figures, male students were largely responsible for the worsened results, while girls surpassed boys in all of the subject areas.
Just five years ago the differences between the sexes were virtually negligible, with boys only a little bit ahead.
It was in 2015 that the tested girl students began to do better than boys in the subjects of maths and natural sciences, the researchers said.
Also, the proportion of boys who have excellent skills has declined, and that's the main reason which caused boys' TIMSS scores to go down, according to Jyväskylä University's TIMSS national coordinator Jouni Vettenranta and project researcher Jenna Hiltunen.
Lower overall scores
Overall, Finnish children slipped from third to fifth place in natural sciences and in mathematics they dropped from eighth to 13th place.
Among the leading academic test-scoring countries, Finland is the only one that has seen test results of fourth graders decline for four years in a row.
Vettenranta and Hiltunen said that the TIMSS study shows that the differences between fourth graders' abilities can be seen before they even start school.
Young pupils who have solid reading and math skills before the first grade do much better on the exams than those with weaker basic skills. Children's' educational careers begin at home even before entering the school system.
Adequate learning materials and resources at home - as well as parents' attitudes toward learning - have significant effects on a child's development at school, the TIMSS researchers said.
Some good news in the details
There was some good news for Finnish educators in the new results; the study found that differences of test scores between regions across Finland are minimal - a situation which barely change over the course of the study.
Overall Finland's educational system appears to remain at a good level. Finland is still in second place regarding natural sciences and maths among OECD-nations and far above OECD-nation averages.
The TIMSS study is published every four years, based on tests taken by more than half a million students aged 9 to 14 in nearly 50 countries. In Finland some 5,015 fourth graders from 158 schools participated in the study.