This paper discusses the contribution of school-based mother-tongue literacy to the maintenance and renewal of endangered languages, with Navajo as the case in point. Although Navajo claims the most speakers among U.S. indigenous languages, the absolute number and relative proportion of Navajo speakers have declined drastically in the last 30 years. Language usage varies across the Navajo Reservation, depending on individual community histories and contact with English. English dominates the print environment, although other forces reinforce the primacy of oral Navajo. Historically, the single most harmful factor for language maintenance was forced English-only schooling. Following a shift in federal policies, the Rough Rock Demonstration School in Arizona was founded in 1966 as the first tribally controlled school, one that reinforced Navajo language and culture in the classroom. After years of fluctuating funds and services, Rough Rock's bilingual program has been reinvigorated by a cadre of local bilingual educators. The K-6 two-way bilingual program develops children's oral and written Navajo and English proficiency and features high-quality exposure to spoken Navajo, teacher-developed Navajo texts, summer literature camps, and the involvement of elders as teachers and counselors. Such practices elevate the moral authority and practical utility of the language. Navajo literacy remains confined primarily to the school but supports a sociocultural environment in which young and old share language experiences. Rough Rock evaluative data demonstrate the academic success of bilingual students with a solid foundation in mother-tongue literacy. It remains to be seen whether program graduates pass Navajo to their children as their mother tongue. (Contains 26 references.) (SV)