Finns believe that their schools are the best in the world, but in this, as in many other things, they are guilty of what I think of as Finnish exceptionalism, a pervasive problem in Finnish culture. Americans who put their kids in Finnish schools will often tell you how disappointed they were in the schools.
My guess is that the best schools in the world are probably in the US, maybe the UK. What Finland doesn't advertise is that it doesn't have the best schools, it has the best worst schools in the world, a description I originally heard from Helsinki mayor Jan Vapaavuori, and I think is true. Finns strive for equality, not excellence. On average, they have good schools. That is very different from having the best schools. And if you are average, or even, and perhaps especially, below average, Finnish schools are amazing, and make sure everyone rises to an average.