 O’Brien (2011) states that Wolfensberger's 1972 book, The Principle of Normalization in Human Services, made clear his intention to lead a process of social change to develop community settings and adaptive service practices that would significantly improve the lives of mentally retarded and other impaired people and their families, as well as contribute materially to the longer term process of making deep positive changes in the social perceptions of such people.He was willing to test his theories by putting them into practice at the provincial, state, and local levels.Between 1971 and 1973, Wolfensberger was a visiting scholar at the National Institute on Mental Retardation in Toronto, Canada, where he revolutionized thinking about human services and used his “change agentry” strategies to teach a new generation of human service leaders and potential leaders in both the US and Canada.