With only 2 to 5 percent of children currently speaking Lakota, Thomas Short Bull, president of the Oglala Lakota College, said the time has come to raise the alarm.

As the day begins at the Lakota Language Immersion School, a young boy passes an abalone bowl of sage to each child sitting on the floor in a circle. Children from kindergarten through third grade gather for the morning ceremony with prayers, songs, and a short discussion of things to know and remember...