Why not Belgium? I mean, it's a largely prosperous, small country. Perfect fit for having a good education system. Belgium has some cultural issues but those don't have to affect the quality of education.

The Dutch cliche about Belgian education is that the Belgians only learn facts. That would result in good test results if the tests focus on that (as I'd suspect they do). The other way around the Belgian cliche would be that the Dutch only learn how to BS. I suspect that there's something to both.