This chapter focuses on the project Concepts of History and Teaching Approaches (CHATA) which studied the understandings of historical concepts of enquiry of children between the ages of 7 and 14. The authors focus on the development of children’s ideas on historical explanation and outline three main aims of the chapter. First, they suggest the broad method of development and aspects of children’s notions of historical explanations. Secondly, they discuss the ‘seven-year gap,’ mainly discussed in math and science, which also exists in the study of history. The gap refers to how some seven-year-old students appear to have the same level and sophistication of knowledge as those students who are seven years older. Lastly, the authors aim to offer evidence that students can independently develop ideas about causal explanations of history. The authors begin the chapter by discussing the background and research design of Project CHATA. The authors use the rest of the chapter to discuss and analyze the four phases of results of students’ understanding of historical explanations. They focused on the models of progression, explanation of the outcomes of action, causal structures, rational understanding and the seven-year gap. They conclude by discussing how understanding children’s ideas about history can help in the development of history education, especially moving from an aggregation model to one focused on progression.