He helped develop the new topic of clinical psychology, in 1911 helped to write the first U.S. law requiring that blind, deaf and intellectually disabled children be provided special education within public school systems,[citation needed] and in 1914 became the first American psychologist to testify in court that subnormal intelligence should limit the criminal responsibility of defendants.

His father was gored by a bull when the younger Goddard was a small child, and he eventually lost his farm and had to work as a farmhand; he died of his lingering injuries when the boy was nine years old.

The younger Goddard went to live with his married sister for a brief time but in 1877 was enrolled at the Oak Grove Seminary, a boarding school in Vassalboro.

During his youth he began an enduring friendship with Rufus Jones, who would later co-found (in 1917) the American Friends Service Committee, which received the 1947 Nobel Peace Prize.

After seeking jobs in the Oakland area for several weeks, he was surprised to receive an offer of a temporary position at USC, and there he taught Latin, history and botany.

][4] At the May 18, 1910, annual meeting of the American Association for the Study of the Feeble-Minded, Goddard proposed definitions for a system for classifying individuals with intellectual disability based on intelligence quotient (IQ).

He had studied the background of several local groups of people that were somewhat distantly related and concluded that they were all descended from a single Revolutionary War soldier.

While the book rapidly became a success and was considered for making into a Broadway play, his research methods were soon questioned; within ten years he came to agree with the critics and no longer endorsed his conclusions.

Although he believed that "feeble-minded" people bearing children was inadvisable, he hesitated to promote compulsory sterilization – even though he was convinced that it would eliminate intellectual disability – because he did not think such a plan could gain widespread acceptance.

The purpose of the program was to identify "feeble-minded" persons whose nature was not obvious to the subjective judgement of immigration officers, who had previously made these judgments without the aid of tests.

[8] He also noted that the population he studied had been preselected, omitting those who were either "obviously normal" or "obviously feeble-minded", and stated that he made "no attempt to determine the percentage of feeble-minded among immigrants in general or even of the special groups named – the Jews, Hungarians, Italians, and Russians"; however, he immediately followed this up by stating that "the figures would only need to be revised (reduced) by a relatively small amount" because "[very obviously high-grade intelligent immigrants] were so small a part of the group [of Ellis Island immigrants] that they did not noticeably affect the character of the group."

The untrue claim that this referred to findings made by Goddard in respect to the greater population of Jewish, Hungarian, Italian and Russian immigrants has been widely publicized.

He devoted the later part of his career to seeking improvements in education, reforming environmental influences in childhood, and publicizing better child-rearing practices.