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 went to 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.”

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Morongo Casino Resort and Spa during sunrise.

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A scene from California's Morongo Indian Reservation: A coyote skin lays atop a stop sign.

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Jisella Martin (left), 6, plays rock, paper scissors, with Angelina Martin, 6, during recess at the Morongo School.

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Mason Evans, 9, front, and Pedro Hernandez, left, 4th grade, and Daniel Marcotte, 4th grade dance with their classmates during the bird songs at the Morongo School.

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Mason Patterson, the principal of the Morongo School, a pre-K-9th grade school run by the tribe, talks about his school with a reporter. Mr. Patterson got his start with the tribe as a tutor working with Morongo students attending regular public schools nearby.

As Indian gaming has expanded rapidly across the U.S. over the past 25 years, some tribes like Morongo have been sinking their newfound resources into education programs and taking advantage of their sovereign status to build schools, hire teachers, and create a curriculum that they believe best serves their children.

For the Morongo tribe—with a sophisticated business portfolio that now includes a bottled-water operation, skilled-nursing facilities, and agriculture—raising a new generation of entrepreneurs and well-trained leaders is critical to sustaining its enterprises.

“We’d known for years that the public schools weren’t equipped to teach most of our children, because our kids were failing,” says Robert Martin, the longtime chairman of Morongo’s tribal council.

“We wanted to take control of how to educate our young people,” he says.

The Morongo tribe is among the wealthiest and most influential in both California and the nation. It was the tribe’s 1987 U.S. Supreme Court case, Cabazon v. California, that produced a ruling that state and local authorities could not shut down bingo operations and other gaming ventures on reservations. That led to federal legislation that threw open the doors to the gaming industry for tribes across the country.

More than 230 tribes operate about 400 casinos now, says Steven Andrew Light, a co-director of the Institute for the Study of Tribal Gaming Law and Policy at the University of North Dakota in Grand Forks.

“If you look at gaming as an economic-development tool, nothing has impacted tribal communities more,” Mr. Light says. “And tribes across the United States have made their own decisions on how to allocate their revenue, but the key pillars for investment have been housing; public services such as roads, police, and fire protections; and education programs.”

Having started with a modest bingo parlor in 1983, the Morongo tribe opened a $250 million casino and hotel in 2004 and now employs roughly 3,000 people in the region. Its business enterprises—primarily the Morongo Casino, Resort, and Spa—are estimated to generate $3 billion in economic activity annually, according to an economic impact study commissioned by the tribe.

Enrolled members of the tribe receive regular “per capita” payments—Morongo leaders will not disclose how much—that provide most families with a comfortable living. Since 1996, the tribe has required members who turn 18 to earn a high school diploma or a GED credential before they can receive the payments.

On the reservation, though, many people are loath to forget the hardships that dominated the tribe’s existence for generations. Families have built new, multilevel homes right next to the dilapidated houses and rundown trailers that sheltered them in more difficult times.

Yet economic success did little to move the needle on academic achievement for most of the tribe’s young people, even though they were growing up in far more privileged circumstances than their parents and grandparents enjoyed.

Tribal leaders know only anecdotally that graduation rates were low and that too few young people were enrolling in college and earning degrees, even though the tribe covers all college and living costs for its students who enroll. (The tribe also fully pays for other postsecondary options, such as trade schools.)

The tribe had already been running a preschool for 3- and 4-year-olds, right on the reservation. And it had created and expanded a successful tutoring program in the late 1990s.

Working closely with the Banning school district, tutors hired by the tribe went into the schools with Morongo children to offer them supports, both in the classroom and outside of school, says Mr. Patterson, the Morongo School’s principal, who began his career with the tribe as one of those tutors.

Tutors came to know students and their teachers, and provided a link between reservation families and the local schools. Graduation rates for Morongo students started to rise.

So when the tribe began serious discussions about starting a school, the community immediately bought into the idea, Mr. Patterson says.

“There was a lot of trust already that the tribe itself was in the best position to educate its own children,” he says.

In 2012, the school received a three-year accreditation from the Western Association of Schools and Colleges, the regional accreditation agency.

Growth in mathematics and reading performance has been strong, according to the school’s own data. At the end of 2011, the school’s first year, only around 30 percent of students—at the time, there were 23 students in grades K-6—were reading and doing math on grade level as measured by their performance on the Stanford Achievement Test. Two years later, 61 percent of students were performing at grade level in math; 51 percent were doing so in reading.

For tribe member Norman Toro the school offers the promise of radically changing his family’s education trajectory in one generation.

Forty years ago, Mr. Toro was an 8-year-old boy living in a crowded, ramshackle house on the reservation with his extended family. He was a high school dropout before he turned 16.

“I spent a lot of time up in the canyons hunting with my uncles,” Mr. Toro says, “but when it came to my education, I didn’t spend too much time thinking about it.”

Now his 8-year-old daughter, Vanessa, is a 3rd grader at the Morongo School. Mr. Toro marvels at how much she loves school and how quickly she is absorbing the Cahuilla bird songs and language that he never learned.

“If I had had this school,” he says, “I think I would have had a shot at graduating.”