This is partly a biography and partly a useful history of the intellectual and political battles over the disabled. (I found the book classified in my library as Dewey Decimal 362: social problems and services to groups of people.) It's a complicated book about a complicated topic, and can't be summarized.
Although other authors have told the history of the eugenics movement and the evils it enabled, such as anti-immigration laws and standardized intelligence testing, Green's book is useful for its focus on the helping professions (medicine, psychology, social work, education) and their participation in both the destructive movement and criticism of it.
Like many institutions, the school that Fernald founded, and that later was named after him, started with progressive values and adequate funding. Part of its degeneration was caused by overstuffing it with people who were diagnosed improperly, and the decline in funding so commonly seen in social services. As Green points out, Walter Fernald's natural empathy and humanity battled within him with racism and prejudice against the disabled.
The book ends by showing that the abuses of the past are still with us, although there is much less institutionalization.