>>one of the reasons why the Finnish school system seems to do such a good job is that due to still a pretty strong ethnic homogenity, most kids have the chance to learn on their own language<<
Told ya so. Not a big mystery.
Homogenity is one of the reasons American private schools can do better than public schools, even with smaller budgets. American public schools are obliged to take all comers, dysfunctional or not, but private schools just toss out those who don't want to be there. Guess where they end up? (I have a relative who's a HS principal who goes stark raving mad at comparisons of American school public/private test scores.)
Re: Scale. Many American institutions are determined by scale. In a national institution (like public ed) much strategic direction is centralized in Washington. Local direction often deteriorates to rubber stamping the wishes of public employee unions. This creates a certain amount of turmoil at the local level over what is taught and who gets to say so. It's also seen in medical care. Americans ask, "Why can't we have a medical system like France?" "Because," comes the reply, "France is about the size of Ohio."
I think the real reason Finland is a land of peace-loving people is that the females are such stunners that the men are perpetually kinda tired, even the homely ones that an American stunner wouldn't even put on her alternative list. It's Darwinism at work.