ABSTRACT
Competence with rational numbers greatly contributes to later mathematical achievement. Competence with rational numbers is also important at workplace. This chapter presents two review papers that discussed difficulties of learning rational numbers from the perspective of the integrated theory of numerical development. It also presents the seven inherent features of fraction and decimal arithmetic that make them hard for many children. The chapter summarizes some empirical data on the difficulties of learning rational numbers among children with mathematics difficulties (MD). It reviews successful interventions on improving magnitude knowledge of rational numbers and discusses implications of the integrated theory of numerical development. Many of the successful interventions on rational numbers share a common feature: a focus on magnitude knowledge of rational numbers with the number line representation. Successful interventions on rational number magnitudes provide hopes for improving rational number knowledge in general and also highlight the use of number lines in representing rational number magnitudes.
