The differential impact of social services on young people's resilience.

Differential Impact Theory (DIT) can help explain which services and supports work best for which young people at which levels of risk exposure. As a complement to a growing understanding of how a child's genetic and phenotypic traits influence treatment outcomes, DIT focuses attention on the relative impact of a child's environment on psychosocial development. In this article, three principles of DIT will be discussed: (1) demands of higher level systems compel individuals to adapt; (2) the factors that influence individual change the most depend on the individual's degree of risk exposure; and (3) the more complex the challenges an individual faces, the more complex the systems required to improve functioning. Two detailed case studies based on interviews and multiple file reviews will be used to illustrate these principles of DIT. Both case studies were drawn from a study of young people (average age 16.1 years) who were clients of multiple social services. While support for DIT requires further study, findings presented in this paper demonstrate the potential of the theory to explain the differential impact of services and supports on young people's developmental trajectories where there has been exposure to high levels of risk. The application of DIT to service design is also discussed.