Indeed, Finland is a model state in so many ways. That is why they can do with schools stuff that likely won't fit the immediate needs of inner-city US minorities: Finns can have short school times because parents have flexible working arrangements, generous subsidies, free healthcare and so on. Finnish kids go home to solid families that can make time for them without sacrificing their wealth; American kids go home to parents who are overworked, absent, or even addicted -- especially the poorer ones. In that situation, it's much better to keep them in school doing activities for as long as possible.

To be honest, you don't even have to go as far as the US, there are very similar issues in European banlieues and the likes. Long school hours used to be a typical postwar demand of progressive worker-rights movements, because it freed parents (especially women) to pursue career advancement and focused kids on academic achievement. I am a product of that sort of system, myself: from the age of 6 to the age of 12, I would be in school from 8:30am to 4:30pm, 5 days a week - plus an optional extra hour at both ends because my parents couldn't pick me up sooner. Unfortunately, after the social regression of the last 20 years, that kind of system is slowly disappearing in Europe too, and for all the bad reasons (cost-cutting).