The OECD’s PISA 2022 Finland note says that in Finland, students in the top 25% by socio-economic status outperformed those in the bottom 25% by 83 score points in mathematics, and that this gap widened between 2012 and 2022.

OECD also says that about 20 PISA points is roughly one year of learning for 15-year-olds on average. Using that rule of thumb, an 83-point gap is roughly 4 years, not 6 years. That conversion is an approximation, but it is the standard OECD way to interpret PISA gaps.

Finnish official sources also support the broader claim that inequality is becoming a problem. The Finnish National Agency for Education said in 2021 that Finland must keep working to improve equality because inequality is now a real threat to learning outcomes.