In 104 acres of boulders, trees and grassy meadows, science teacher Brent Osborn hadn't seen his students for about 15 minutes. He stepped over fallen logs, hiked up steep rises and meandered through thickets, covering a lot of ground at the Pinecroft Natural Area Preserve in Spokane Valley, a fenced-in "biological island" west of the YMCA. But his 60 students remained scattered out of sight on a sunny school day.