In the first episode of G, Radiolab’s miniseries on intelligence, we went back to the 1970s to meet a group of Black parents who put the IQ test on trial. The lawsuit, Larry P v Riles, ended with a ban on IQ tests for all Black students in the state of California, a ban that’s still in place today.

This week, we meet the families in California dealing with that ban forty years later. Families the ban was designed to protect, but who now say it discriminates against their children. How much have IQ tests changed since the 70s? And can they be used for good? We talk to the people responsible for designing the most widely used modern IQ test, and along the way, we find out that at the very same moment the IQ test was being put on trial in California, on the other side of the country, it was being used to solve one of the biggest public health problems of the 20th century.

This episode was reported and produced by Pat Walters, Rachael Cusick and Jad Abumrad, with production help from Bethel Habte.

Music by Alex Overington. Fact-checking by Diane Kelly.

Special thanks to Lee Romney, Chenjerai Kumanyika, Moira Gunn and Tech Nation, and Lee Rosevere for his song All the Answers.

Radiolab’s “G” is supported in part by Science Sandbox, a Simons Foundation initiative dedicated to engaging everyone with the process of science.

Support Radiolab today at Radiolab.org/donate.