We teach it. At least I remember getting some classes about native populations and even more classes theorizing how human rice arrived in America
Really? Wow, I didn't have any classes on that. Exclusively European history until the 16th century... I grew up in the south, though, so maybe that has something to do with it?
We do have some history classes for the more developed indigenous civilization (maia, astecas, melmecas, etc), but that is one that is more romantized, we almost don't get history about brazilian indigenous population because since they didn't have written history and most of their population either died of disease, killed or turned into european civilization very few of their history survived to be told.
If you think hard about our history classes from elementary school to the end of high school all the pre-written story is covered very fast and generic (talk a little about migration moves, that we originate from Africa, a little about cave paiting, the major age marks like stone age, etc) and them each of the older civilization talked had some form of written language, from what was considered the first civilization to have it at time I was in school (mesopothamian), then egypt, then greek, macedonian, rome, very few of china and mongolia (almost nothing of the rest of eastern civilizations, almost nothing of other africa civilizations)....