Ninety miles east of downtown Los Angeles in the San Bernardino Mountains, a school for Native American children peers down onto its main benefactor, a glittering, Las Vegas-style casino and hotel owned and operated by the Morongo Band of Mission Indians. Millions of dollars spent in the casino by gamblers playing the slots, shooting craps, and wagering on poker hands are flowing into the Morongo School and fueling what could be the tribe's most important enterprise yet: taking control over the education of its own children.

The Morongo School—which opened in 2010 on this 35,000-acre reservation tucked into a narrow pass between the San Bernardino and San Jacinto mountains—is the Morongo tribe's biggest bet at the moment. After nearly 20 years of stunning economic development and the virtual elimination of poverty for its 1,000 members, the tribe is investing millions of dollars in education in the hope of reversing decades of low academic achievement, high dropout rates, and low rates of college attendance and graduation for its children.

On a drizzly October morning on the reservation, school bus No. 5 rolls up in front of the beige portable buildings that house the Morongo School's lower grades. Principal Mason Patterson and faculty members greet the stream of children and lead them through an open courtyard with expansive views of the mountains, covered with red oak, creosote bushes, and pinyon pine. The entire student body is 140 children, ranging from preschool through 9th grade. Older students now either attend public high schools nearby or use an independent-study program to earn their diplomas. The Morongo School will graduate its first class in 2017.

No class has more than 15 students, and every teacher in the lower grades has an aide. The school has adopted the Common Core State Standards, and its classrooms are outfitted with up-to-date educational technology, including iPads and Apple TVs. Completely funded by the tribe and available at no cost to children with a parent who is an enrolled member, the school operates mostly free of state and federal requirements around academic standards and accountability.

"We didn't want any government money," Mr. Martin says. "We didn't want the curriculum controlled by anyone else, and we know we are fortunate to be in that position."

"I think our small class sizes are so important," says 4th grade teacher Christina Alaniz, who grew up on the reservation and wentto public schools.

"We really know our students, and they really know each other well, too." Twice a week, tribal elders spend the day with Morongo students, teaching them the nearly extinct Cahuilla (ka-wee-yah) and Serrano languages and cultural traditions unique to the Cahuilla people, a broader group of Native Americans that includes the Morongo tribe.

Most of the language instruction comes through the teaching of traditional "bird songs," which tell stories, often from the perspectives of birds, of journeys that the Cahuilla people would take from their desert and mountain homes and about the creation of the natural world.

Bridging cultural distances between the students and their heritage—which grew as tribal members' married outside the community and moved from the reservation—was another driving force behind the tribe's push to create its own school, says Mr. Martin, the tribal-council chairman.

California is home to more Native Americans than any other state, and most tribal children are enrolled in public schools scattered across cities, suburbs, and rural areas—often with few other Native peers. In Riverside County, where the Morongo reservation is located, American Indian students make up less than 1 percent of public school enrollment, even though there are 12 federally recognized tribes in the county.

For Morongo children, most of whom attended the public schools in nearby Banning before the Morongo School opened, that disconnection from their heritage contributed to feelings of isolation and low self-esteem, Mr. Martin says. Tribal leaders believed that young people were not getting enough meaningful exposure to the history and experience of California tribes, which was affecting their achievement. And those youths were increasingly facing a new stereotype: the rich Indian.

"I saw it happen with my own daughter," Mr. Martin says. "She wanted to quit school in the 9th grade because of negative comments she heard a teacher make about Indians. We had to enroll her in independent study so she could finish."