A few quick pieces of background information. There are currently 562 recognized Indian Nations ("variously called tribes, nations, bands, pueblos, communities, racherias, and native villages") in the states. (source) All of which, and then some, were around during the 20th century. While there is overlap, each nation has its own language, culture, and society. So, the nature of the change for a given community depended on a number of factors including their proximity to European Americans, population size, and philosophy around assimilation versus isolation. In effect, a great deal of the 20th Century for American Indians was about avoiding genocide and extinction.

That message around trying to stay alive can be found in the writings about Native Indian parents making choices about sending their children to federally-run Indian Schools. Tribal leaders praised the boarding schools for preparing indigenous children for life in America despite the harsh conditions while parents feared what would happen if they didn't send them. (Coleman, 2006)

In 1938, the US Department of the Interior asked Lewis Meriam to study the history and current state of education for Native Indians in the country and his report, known as The Meriam Report, details the abuse and indignities white Americans subjected the country's indigenous people to in the name of "progress." (Fraiser, 2014) His report strongly advocated for providing educational opportunities for children back with their families and spoke of different approaches for different communities. He wrote, "Indian tribes and individual Indians within tribes vary so greatly that a standard content of education and method of education, no matter how carefully they might be prepared, would be worse than futile."

Hope this helps give a sense of the big picture, if not specifics!

Source: Fraser, J. W. (Ed.). (2014). The school in the United States: A documentary history. Routledge.