Immigrants tended to concentrate in certain areas, causing some schools to become much more mixed than others, yet there has not been much change in the remarkable lack of variation between Finnish schools in the PISA surveys across the same period.
This is only because there are still very few immigrants in Finland. In actuality, immigrants to Finland score about 50 points lower on Pisa than Finnish natives (about double the gap in the US).
(For comparison, the gap between Americans of European descent and non-immigrant Finns in Pisa scores is 22 pts, and the gap between European Americans and Greeks (the lowest performing European nation) is 46 pts. )
http://super-economy.blogspot.com/2010/12/amazing-truth-abou...