This paper proposes an approach to diagnosing learning disabilities that measures the intrinsic processing or capacity weaknesses that are presumed to underlie academic performance problems. This approach is contrasted with the "diagnosis by exclusion" method currently used. The paper discusses: (1) a definition of intrinsic processes with distinctions between them and other kinds of mental processes; (2) evidence for intrinsic processing weaknesses as the cause of specific learning disabilities; (3) advantages of a processing approach to diagnosis over current discrepancy-based approaches; (4) difficulties involved in using direct assessment of intrinsic processes to diagnose learning disabilities; (5) alternatives to classification based on assessment of intrinsic processes; and (6) threats to the concept of specific learning disabilities at the levels of science and educational practice arising from a decision to eschew the assessment of intrinsic processes as part of classification procedures. The paper also addresses the consequences for the field of learning disabilities of changing the procedures for classifying these children. (DB)