Mentally deficient was a term used for much of the twentieth century to describe people with intellectual disabilities.
In 1920, the Mental Deficiency Act, which established a Mental Deficiency Board to oversee the classification and management of people with intellectual disabilities, gave the term legal force. The Act also established the State Psychological Clinic which diagnosed children and adults as mentally defective.
The term mentally defective appears in case files kept by the Mental Deficiency Board. It also appears in the case files of state wards diagnosed with intellectual disabilities.
Children diagnosed as mentally defective often did not have an intellectual disability. Challenging behaviour, inadequately managed physical disabilities such as deafness, educational disadvantage, an institutional upbringing, and poverty, neglect or abuse could all lead to this diagnosis.
Prepared by: Caroline Evans
Created: 25 October 2011, Last modified: 5 March 2015