> the Netherlands, parts of Denmark, or perhaps Japan

I think it's far more common than that -- actually, guessing wildly, I suspect most children around the world get themselves to school and that the US is the outlier.

In Germany, where I live, and where my oldest will be starting school in two months, it's common and encouraged for kids to walk to school in their first year (age 6). Admittedly, ours is only a quarter mile away. We've just started letting our son go alone to the bakery downstairs and across the street from our apartment, and while it's not quite typical, it's also not wild here for a 5 year old to do that.