Although there are exceptions, procedural skill and conceptual understanding usually are highly correlated. One source of evidence for this view is cross-national studies. For example, comparisons of Korean and American elementary school children have revealed parallel national differences in conceptual and procedural knowledge of multidigit addition and subtraction. Fuson and Kwon (1992) asked Korean second and third graders to solve two and three digit addition and subtraction problems that require carrying or regrouping.