The two chapters which comprised part I of this book advanced arguments for adopting a developmental perspective towards everyday physics. In particular, these chapters tried to show that a developmental perspective should generate material of great relevance to both psychological theory and educational practice. However, while the appropriateness of developmental research was strongly defended, the chapters in part I did not advocate investigation across the full age range. They argued that the minimally verbal techniques favoured by some developmental psychologists would probably not permit unambiguous answers to the significant problems. Follow-up questioning would almost certainly also be required. However, the use of questioning with the preschool-age group could generate difficulties. At this age level, command of language is not necessarily secure. Moreover, the key issue with regard to preschoolers is of the presence vs. absence type, meaning that the danger of distortion due to language problems is particularly acute. With school-age children, language skills are obviously more advanced, and the key issues at this age level rest on language being used in one way rather than another. Acknowledging this, part I advocated research with school-age samples.