The cutoff method was used on longitudinal data in more than one content domain in a study attempting to determine whether the effects of schooling are general or limited. Conservation of number, an informally acquired skill, and mental addition, a formally acquired skill, were evaluated among older kindergarten children, younger 1st-grade children, and older lst-grade children. Older kindergarten children and younger 1st-grade children were about the same age; younger and older lst-grade children had the same amount of schooling. The conservation data indicated that improvements in performance were due primarily to age rather than schooling, and improvements in the accuracy of mental addition were due primarily to schooling rather than age. This pattern of results has three implications: (1) young and old children are equally ready to benefit from the kinds of counting and arithmetic operations that are emphasized in school; (2) schooling seems to have relatively specific effects on performance; and (3) the cutoff method can be quite useful for discovering which kinds of skills are acquired as a function of schooling or age, and for addressing questions about children's readiness for acquiring certain kinds of knowledge. It is concluded that as results accumulate, priority should be given to the construction of a coherent picture of the effects of early schooling on cognitive and academic development. (RH)