This paper examines the growth and development of the Arapaho immersion program and discusses language revitalization strategies and methods used on the Wind River Reservation (Wyoming). Following a community request for an Arapaho language and culture program in reservation public schools, a test class of kindergarten students received an hour of Arapaho instruction daily for 18 weeks. After 12 weeks, 80 percent of students had mastered 162 words and phrases. These favorable results plus information from Hawaiian immersion programs led to implementation of a half-day immersion kindergarten class in September 1993. A belief in the need to increase students' language contact hours led to a preschool immersion class; a summer program; and finally, a 6-hour-a-day school immersion program. Although children in the expanded school program greatly increased their mastery of Arapaho, they did not come close to fluency because they lacked the ability to independently use and manipulate new speech forms. In 1996, a trainer from the Hawaiian language immersion system was hired to guide and train staff in proven immersion techniques, and a second immersion class was begun on another part of the reservation. Both classes made astonishing progress, but fluency was again elusive. To achieve fluency, children must be systematically exposed to a full array of speech forms by a well-trained teacher with a clear understanding of language acquisition. Thus, effective teacher training remains a critical issue for language immersion programs. Implications of the enormous success of Maori immersion efforts are discussed. (SV)