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Arithmetic and cognitive skills of children with mathematical difficulties (MD-only), with comorbid reading difficulties (MD-RD), with reading difficulties (RD-only), and normally achieving children were examined at 3 points from Grades 3-4 to Grades 5-6 (age range, 9-13 years). Both MD groups displayed severe weaknesses in 4 domain-specific arithmetic components (factual, conceptual, procedural, and problem-solving skills) during all 3 measure points. Telling time and approximate arithmetic were also problematic for children with MD. Both MD groups displayed a small weakness related to visual-spatial working memory, and the MD-RD group also displayed small weaknesses related to verbal short-term memory, processing speed, and executive functions. The 4 groups developed at similar rates within all domain-specific components as well as basic cognitive functions. These findings demonstrate that children identified as having MD when they are 9 years old do not catch up with their normally achieving peers in later school grades, when they are 13 years old. They also continue to lag behind their peers with respect to the domain-general cognitive system.
Supplemental materials: http:dx.doi.org/10.1037/a0016838.supp
