I think it's likely a post code (ZIP Code) lottery. Depending on where you live will determine where you end up. To be fair, my daughter who's only 5 is light year's a head of where I was at her age. But she goes to a faith school where as I just attended a bog standard one.
Re geography, might it be that US citizens tend not to travel abroad? I live in UK which isn't very big and so become more aware of other countries and their locations. The US is frickin massive and contains pretty much all you need (subtropical, desert, grassland, Mountains et etc)