WARM SPRINGS, OR—Members of the Confederated Tribes of Warm Springs have decided to spend nearly $11 million to build a new school. The vote was essentially a re-do of a referendum that failed in May due to inadequate voter turnout.

Nearly three quarters of the tribal members who cast a vote in that first election favored the plan. Still, it failed due to a provision in the tribes’ constitution that requires at least 33 percent of all members over the age of 21 cast a ballot. Just by comparison, only 22 percent of registered voters turned out in Multnomah County for the May primary. And that p...