Research on learning disabilities (LD) depends upon a conceptual framework that specifies what it should explain, what kinds of data are needed, and how these data are to be arranged in order to provide a meaningful explanation. An argument is made that LD are no different in this respect than any other form of human illness. In this article, a theory of LD based on weak normativism drawn from the philosophy of medicine is presented. This theory emphasizes that cultural values (norms) determine which aspects of human experience and function are instances of ill health. Thus, ill health is fundamentally normative. However, the experiences and behaviors themselves arise out of the natural world and therefore can be explained by a culturally neutral natural science. Data from a longitudinal study of specific language impairment are used to show that academic achievement is culturally evaluated, that low achievement is disvalued, and that therefore actions are taken to help the poor achiever. Spoken language abilities in kindergarten are associated with judgments of the adequacy of fourth grade academic achievement and are mediated by reading prior to fourth grade and also via a path that is independent of reading. It is argued that poor academic achievement may be viewed as a disvalued state consistent with an illness, whereas language and reading skills can be viewed as basic causal systems that can explain the child's learning performance. Properties of this causal system are value free, except that they can inherit disvalue by their association with poor achievement. It remains to be determined whether the notion of LD is to be equated with poor achievement and therefore serve as a type of illness or whether it is to be viewed as a particular cause of poor achievement and thus functions as a type of disease associated with poor achievement. The conceptual framework lays out the alternative meanings for LD and the choice between these alternatives will ultimately depend on how it is used in the LD research community.