How can new historical interpretations be more valid than older ways of understanding the past? Objective As a result of this lesson plan, students will… 1. Determine key information in historical texts. 2. Analyze the impact of the inclusion and exclusion of specific details in a text. 3. Infer the author’s purpose and extrapolate the impact of the historian’s decisions. Background Historians' work involves investigating the past by analyzing different kinds of evidence to get as complete an understanding as possible, much like how detective work involves seeing how different clues all fit to Duration: 60 Minutes.