http://www.sedl.org/pubs/sedletter/v11n01/3.html

A New Mexico principal tells the story of an American Indian kindergartner.
When shown pictures of four common objects during an assessment of early
reading skills, the child described the objects vividly without ever using
the names of the objects. That the child was able to do so reflects the
powerful oral tradition of his native language, Keres, and his fluency in
that language.

Coming from an oral tradition means the child is likely to have received
less exposure to print than a child whose primary language is oral and print
based; this background is an indicator that he might have difficulty
learning to read English. The principal wants to ensure this child’s reading
success, but also wants the student to maintain and preserve the language of
the tribe. His dilemma is one shared with educators across the United States
who teach an increasingly diverse student population.