Here are some analyses which try to explain Finlands success in PISA if you are interested. The third book is a very recent report of what can be done to decrease the difference in result between swedish- and finnish speaking schools. The last report is also in swedish.
The Finnish Education system and Pisa
Differences in the results between Finnish and swedishspeaking schools
Jämlikhet och reultat Forskningsresultat som kan användas för att minska skillnaderna
i PISA-prestationer mellan svenskspråkiga och finskspråkiga elever