For an excellent discussion of how biased our textbooks are, read Lies My Teacher Told Me by James Loewen. No teacher should claim or believe a textbook is fair and impartial. Not without analyzing it the way Loewen did.
For more on the subject, see The Harm of Native Stereotyping: Facts and Evidence.
P.S. I guess Iowa's schools don't teach proper capitalization or punctuation either. <g>
Below: What kids are still learning today?