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.

Neurobiological theories look at the impact of biological and genetic factors on individual differences. Psychodynamic theories emphasize the need in developing skills in self-regulation of impulses and enhanced awareness of others. Cognitive theories look at the relationship between thoughts and behaviours and how faulty assumptions can impact social relationships. Social cognitive theories emphasize the importance of social interaction in the development of a child. Cognitive behavioural theories emphasize associations between thoughts and behaviours.

Behavioural theories state that behaviour is shaped by associations (i.e. contingencies) resulting from positive and negative reinforcement.

A behaviour is in excess if there is externalizing behaviour (e.g. too much of something) or a deficit if there is internalizing behaviour (e.g. too little of something). It is often more successful to increase certain behaviour than to reduce behaviour.

According to Erikson, children develop through psychosocial stages with socioemotional tasks that must be mastered to allow for positive growth across the lifespan (e.g. trust vs. mistrust). The adaptation theory states that early attachment relationships has an impact throughout the lifespan. Triadic reciprocity refers to the dynamic system between the person, environment and behaviour where all three influence each other.

Family systems theory states that the family is a system made up of subsystems (e.g. parent and child). Behaviours in a system are aimed at maintaining or changing boundaries, alignment and power. A family’s degree of dysfunction can thus be determined by boundaries that are poorly or inconsistently defined.

Equifinality states that several developmental pathways may produce the same outcome (e.g. ADHD). Multifinality states that similar factors may produce different outcomes (e.g. neglect can lead to aggression or withdrawal). Reciprocal determinism refers to the bidirectional nature of influence (e.g. child influences a parent and a parent influences a child).