This article reports on an obstacle to achievement that seems particularly pronounced among Native American students high mobility. The turnover rate for one school, North Middle School in Rapid City, South Dakota, was 50 percent overall last year--meaning that half the school's 468 students came or went after the start of the school year. Many of them were Native Americans. And instability carries a cost. The steady coming and going of students is one reason the school has always failed to make adequate yearly progress, or AYP, goals under the federal No Child Left Behind (NCLB) Act. To improve student achievement, North Middle has launched new teaching strategies, after-school tutoring, and family-outreach efforts that--if successful--could hold lessons for other urban and low-income schools with high student turnover.