The correct answer to this open question is the following.
The reason why Native American children were sent to Indian schools in places like Carlisle, Pennsylvania was to make Indians accept white culture by cutting ties with their own culture.
Carlisle Indian School in Pennsylvania was the main Indian boarding school from 1879 to 1918. The government sent children to this kind of schools because it wanted to incorporate them to the American culture. The government wanted the children to forget their Indian and tribe past and roots to better incorporate into American society, culture, and customs. Some people thought that Indians were hindering the country to evolve to a much modern America and in that time, one way to change them was through American education.