Number and operations serve as the "cornerstone" of the K-12 mathematics curriculum in many countries. Solving problems in the mathematical domains of algebra, geometry, measurement, and statistics is often closely connected to student knowledge of number and operation (Griffin, 2005). Although considerable knowledge exists regarding the development of number and operation for typically developing children, less is known about the development of children who struggle in mathematics. Moreover, children enter school with considerable differences in their understanding of number and operation. While most children, through exposure to various informal and formal tasks, develop a deeper understanding of number and operation, this development is delayed for some children. These children do not achieve levels of proficiency required for higher mathematics. ...Therefore it is critical that difficulties in mathematics are addressed before they become chronic, pervasive, severe, and difficult to remediate" (Fuchs, 2005, p. 351). ...In some studies, concerns regarding student retention of learned concepts, and success generalizing and transferring mathematical ideas to other mathematical situations or domains were noted. Yet it is unclear why these mixed results occurred. ...Therefore, they strongly recommend that, "future research should be directed at the role of individual differences in the development of early numeracy and the characteristics of children's learning responsible for these differences" (Van Luit & Schopmann, 2000 p. 35).