Diagnosis, as applied to reading, is defined as a systematic and rational explanation of an individual's inability to make anticipated progress in learning to read. And, it is noted that diagnosis can be made at four levels: (1) identification of difficulty, (2) classification of disability, (3) determination of specific reading needs, and (4) detection of causal factors underlying the individual's disability. Application of diagnosis to the classroom is shown through the use of school history, objective data, informal inventories, and observation of individuals requiring remediation. An explanation is given of the nature of disability cause and of the techniques of diagnosis. Diagnostic techniques are applied to a group of second-grade children, and means of identifying their reading needs are shown. Application of procedures in the individual diagnosis of a second-grade child with a reading disability is also explained. (WB)