Several neurocognitive abilities, including visual–spatial and language-based processes, attention, and fine motor/finger skills, are thought to play important roles in mathematical development and disability. Evidence for relations of specific neurocognitive skills and mathematical development and disability is presented, with a particular emphasis on findings from longitudinal studies. Why these particular neurocognitive skills are related to math is also discussed. We suggest that mathematics learning in children with congenital and acquired neurodevelopmental disorders, including children treated for cancer, is particularly vulnerable to disruption because these disorders often affect one or more of the neurocognitive systems that support math learning and performance. Implications for assessment of and interventions for math difficulties are discussed. The article ends with implications for mathematical functioning in children treated for acute lymphoblastic leukemia and brain tumors. Pediatr Blood Cancer 2014; 61:1729–1733. © 2014 Wiley Periodicals, Inc.