Every year since then we have made a point of looking into these questions, at first with little hopes of success because, as we quickly discovered, the time relationships constructed by young children are so largely based on what they hear from adults and not on their own experiences. But when, after trying to apply the idea of ‘groupings’ to the development of the child’s conception of number and quantity, we went on to apply it to the concept of motion, velocity and time, we discovered that the problems of duration and temporal succession had become greatly simplified. The results are presented in this volume.