The study that is the subject of this document focused on how fifth-graders' knowledge and thinking about the westward expansion of the pre-Civil War United States was affected by students' participation in a curriculum unit on the topic. A stratified sample of 10 students was interviewed before and after they participated in the unit to determine, first, what they knew (or believed was true) about the subject and second, what they learned about it. Prior to the unit, students' knowledge about U.S. history was focused on events that occurred east of the Appalachian Mountains, except for what they may have remembered from a unit on Michigan history that they studied as fourth graders. Through the unit, students learned a great deal about the Wilderness Trail, the Louisiana Purchase, the Lewis and Clark expedition, the war against Mexico, the California gold rush, and the transcontinental railroad. While there were few outright misconceptions on such topics among the students, they had not yet developed a rich context of background information within which to assimilate what they were learning about westward expansion of the new nation. In particular, they could have used more information about the pioneers' tools and supplies, the federal role in westward expansion, and the fate of various Native American tribes whose traditional lifestyles came under increasing pressure as frontier lines advanced. (Contains 22 references.) (Author/LBG)