In 1943, Clark graduated from Columbia with a PhD in psychology, making her the first black woman to do so.
But it was the work she did with Kenneth, namely the Doll Test, that has had the most lasting impact on the field of psychology and on the Civil Rights Movement. The Doll Test looked at 253 black children aged three to seven years old: 134 of the children attended segregated nursery schools in Arkansas and 119 who attended integrated schools in Massachusetts. They each were all shown four dolls: two with white skin and yellow hair, and two with brown skin and black hair. Each student was asked to identify the race of the doll and which one they preferred to play with.
The majority of the black students preferred the white doll with yellow hair, assigning positive traits to it. Meanwhile, most discarded the brown doll with black hair, assigning it negative traits. The Clarks concluded that black children formed a racial identity by the age of three and attached negative traits to their own identity, which were perpetuated by segregation and prejudice.
Leading up the 1954 ruling in the Supreme Court ruling of Brown v Board of Education, Clark and Kenneth testified in many school segregation cases in the South. one particular case, Clark was called to testify in the desegregation case of Davis v County School Board of Prince Edward County Virginia to rebut the testimony of none other than her former advisor, Henry Garrett. He testified in favor of segregation, arguing that black and white children were innately different. Clark argued against his testimony directly, and the court ruled in favor of integration. That was last time Clark and Garrett would meet.
In regard to the Brown ruling itself, the NAACP lawyers asked Kenneth to pen a statement that described the social psychology research that supported school integration, which included the Clarks’ research and the Doll Test. Rutherford says that the work “was quite influential as part of the integrationist case in the Brown v Board decision. It was also the first time social science research was used in a Supreme Court Case.” Yet while history books often credit Kenneth with the Doll Test, even he acknowledged that “The record should show [The Doll Test] was Mamie’s primary project that I crashed. I sort of piggybacked on it.”