I've been discovering that the American History I was taught growing up is not all necessarily accurate. I homeschool my daughter and have been putting off NA History for quite some time as I want to teach her accurately, but am so overwhelmed with information and where to start and I want to be comfortable and confident in what I am teaching her.
I do not think you can go wrong with Charles Mann's 1491: New Revelations of the Americas before Columbus. Here is an NPR interview with the author about the book. It should give you a taste. It is a truly marvelous book aimed at the educated lay person. It's pretty darn good resource for professionals too.