BISMARCK, N.D. -- Saje Beard's half-hour commute to class is the envy of her four classmates at a one-room schoolhouse just south of here. Most mornings, the third-grader makes the trek on Ruth the mule. "She's called many things, but Ruth is what we call her in public," Saje said of the 4-year-old gray mule. "Actually, that's my dad's joke. She's really nice and gentle. And she sure is smart." Saje, 9, is an old hand at maneuvering mules. She's been doing it since she was in first grade. "I feel more safe with her riding a mule than having...