Goddard established one of the largest training schools for the mentally disabled (i.e. extremely low IQ) but did much to harm the attitudes towards these people. There were several obstacles that prevented child psychopathology to become a unique discipline:

1. The nature-nurture debate about the origins of a child’s problem.
2. The shift in emphasis from treatment to identification (i.e. identified from an adult perspective).

Developmental psychopathology defines a system on human development as holistic (i.e. the whole child needs to be looked at) and hierarchical (i.e. moving toward increasing complexity). Recently, emphasis has been placed on finding protective and risk factors for the development of maladaptive behaviours in children.

To diagnose a child, information is necessary from several sources (e.g. school, home environment, sport team) to get a holistic image of this child. A case formulation refers to a hypothesis about why problem behaviour exists and how it is maintained. This formulation should be based on the longevity of problems (1), consistency of problematic behaviour across situational contexts (2) and family history (3).

To understand whether a behavioural pattern is normal or abnormal, it is essential to have an understanding of the range of behaviours normal at a certain age. Comparing behaviour to normal expectations can be done by using the four d’s, namely deviance, dysfunction, distress and danger.

1. Deviance
   This refers to determining the degree that behaviours are deviant from the norm. This can be done using both informal testing (e.g. interview) or formal tests (e.g. test batteries). Classification systems can be used to determine degree of deviance.
2. Dysfunction
   This refers to assessing the relative impact of a disorder after the disorder has been identified (e.g. impact on academic achievement).
3. Distress
   This refers to assessing the distress that a disorder causes. This is difficult to assess in children so extra forms of information (e.g. teachers) may need to be used.
4. Danger
   This refers to assessing whether there is risk for self-harm (1) and risk of harm to others (2).

Clinical decisions are often based on measures of the intensity (1), duration (2) and frequency (3) of the behaviour relative to the norm. The developmental stage of a child needs to be taken into account.