Learning mathematics means being able to interpret mathematical structures and discover relationships within them. Modern mathematics instruction, therefore, is not limited to conveying procedures and rules; it aims to enable children to construct mathematical knowledge independently and actively. But how can learning processes be designed so that children gain insight into mathematical structures? This book addresses this question within the research tradition of Heinz Steinbring, where the individual development of mathematical concepts is not confined to series of tasks for independent work, but rather interactive encounters between children are seen as central to the further development of mathematical knowledge. It is precisely these discussions about mathematical problems that provide the foundation for the development of individual understanding.