Beginning teachers in Northern Ireland and the United States conducted structured inquiry projects in which they investigated elementary children's understanding of history and social studies. Interviews with the teachers and analysis of their written assignments indicate that these investigations challenged their beliefs about children's prior knowledge and their own instructional techniques. Teachers initially believed that inadequate cognitive development and lack of background knowledge limited children's ability to understand history and social studies; however, after taking part in these projects, they developed a new appreciation for children's prior ideas and a clearer commitment to their own role in building on that knowledge. These findings suggest that structured investigations, focused on specific disciplinary content, have the potential to encourage beginning teachers' reflection on their students' cognition and to enhance their own sense of professional responsibility.