Lead (Pb) is a potent neurotoxicant, but few studies have evaluated its effect on neurobehavioral measures that can be used in multiple species including humans. We investigated the effect of prenatal and childhood Pb exposure on children's rate of forgetting using a delayed matching-to-sample (DMTS) task among children 6 to 8 years of age. Blood Pb was measured during pregnancy (second and third trimesters) and at 4 to 6 years of age. A nonlinear modified power function was used to predict the forgetting rates on the DMTS task, using separate models for prenatal and childhood Pb. Higher childhood Pb [median (interquartile range), 1.7 (1.3) (μg/dl)] was associated with a faster rate of forgetting (β = -0.05; 95% confidence interval: -0.09, -0.01). Higher maternal intelligence quotient and child's age were significantly associated with a slower rate of forgetting. We validated a unique power function statistical approach for rates of forgetting using Pb exposure.