Initially,children model the action and relations in problems, reflecting the distinctions portrayed in the analysis of problem types. Over time, these physical modeling strategies give way to more efficient counting strategies, which are generally more abstract ways of modeling a problem. Eventually children come to rely on number facts, but the learning of number facts is not necessarily a rote skill. It can build upon an understanding of number relations, which are supported by a foundation of number sense developed through using modeling and counting strategies. Chapter 4 portrays a similar picture of the development of multiplication and division concepts. In Chapter 5 , we return to the notion of problem solving as modeling and examine it in a broader context. Chapter 6 addresses the development of base-ten number concepts and multidigit algorithms. We end with two chapters that discuss how Cognitively Guided Instruction can be applied in the classroom and an Appendix that describes the research basis for this approach