this was at a very well-regarded private elementary school in the midatlantic US (I try not to be any more specific than this on HN, although you can probably figure out the city if you delve deep into my comment history).

I can understand teaching general rules upfront with the expectation that exceptions will be covered later (eg, teaching lower school students that water boils at 212F/100C is okay, they can learn about vapor pressure later). but why would you teach that columbus was the first european to discover north america? not only is it completely wrong, but it's not a practically useful fact, nor does it create a solid basis for deeper understanding.

Because it sounds right to a lot of people.

From experience, this must be true throughout the United States. I went to a very good public school and had similar experiences?