This paper proposes one potential explanation for 100 years of rising population mean IQ in the United States associated with historical changes in access to schooling and educational practice. A neurodevelopmental-schooling hypothesis is forwarded based on evidence of growth in the population's access to schooling early in the last century and the increasing cognitive demands of mathematical curricula from mid-century onward. The fact that these educational changes have been widespread, affect individuals early in the lifespan, and are uncorrelated with genetic propensity for IQ makes them particularly well suited to produce large environmentally driven gains in intelligence between generations in the face of high heritability for intelligence. Future directions for research that would test the neurodevelopment-schooling hypothesis are described.