The decline began in 2006, much before all those “stupid immigrants” could have ruined the system. Immediately jumping to your gut feel hypothesis definitely doesn’t make you a “scientist”.
The immigrants may not be stupid; but they don't, as a rule, come to school knowing finnish. I'd be curious to know how the scores break down based on ancestry of the students.
I find your curiosity curious in this case because it belies the first pass at solving problems involves blaming it on someone else without shame rather than analyzing the system itself.
Try that sentence again; it doesn't scan.
>The decline began in 2006, much before all those “stupid immigrants” could have ruined the system.
The Yugoslav Wars, the Kosovo War and the Second Chechen War were all in 1990s. Many ethnic Bosnians and Kosovarians relocated to Nordic countries during that time.