A retrospective analysis of the case records of 60 pupils at a Speech and Language Unit was used to examine the predictive power of a diagnostic classification system based on deviance and delay. In addition to showing that neither early age of admission nor long duration of stay were associated with favourable outcomes, and that girls were more likely than boys to suffer from additional handicaps, the study identified three major assessment dimensions and linked diagnostic category with both severity of disorder and response to the treatment programme.