We construct a unique individual-level dataset linking preschool blood lead levels with third grade test scores for Rhode Island children born 1997-2005. Using two identification strategies, we show for the first time that reductions of lead from even historically low levels have significant positive effects. A one-unit decrease in average blood lead levels reduces the probability of being substantially below proficient in reading (math) by 0.96 (0.79) percentage points on a baseline of 12 (16) percent. Since disadvantaged children have greater exposure to lead, lead poisoning may be one of the causes of continuing disparities in test scores.