The purpose of diagnosis is to classify the problem within the context of other known behavioural clusters or disorders for the purposes of being able to draw on clinical knowledge regarding potential aetiology, course and treatment alternatives. The purpose of assessment is to diagnose the nature of the problem to ensure that the most appropriate treatment can be selected. There are three questions that need to be answered by the clinician after the assessment:What are the characteristics of the child’s problem?How should the problem be evaluated?What are appropriate intervention strategies?The diagnostic method can be used to predict what types of measures might be selected. Classifying child disorders can be done by using the categorical classification system or the empirical/dimensional classification system. The diagnostic and statistical manual of mental disorders (DSM) and international classification of diseases (ICD) rely on the medical model (i.e. disorder is absent or present). CATEGORICAL CLASSIFICATION (e.g. DSM)Bases of classificationConceptualization of disordersStrengthsWeaknessesObservation (1), matching symptom criteria (2), medical model and diagnostic categories (3) and structured and semi-structured interviews (4).Present or absent (1), qualitative and distinct entities of homogeneous features (2), mutually exclusive distinct boundaries (3).Widespread usage (1), tested using clinical trials (2), comprehensive documentation of disorder features (3).Subjectivity (1), dichotomous (2), mutually exclusive and comorbid disorders (3) and reliability and validity issues (4).DIMENSIONAL CLASSIFICATION (e.g. BASC)Multirater scales (1), factor analysis (2), dimensions/levels/degrees (3), multirater rating scales (4). Continuum or degree of disorder (1), adaptive to maladaptive range (2), empirically based normative benchmarks (3), multirater format (4), focus on syndromes of co-...