Children with higher exposure to Black Carbon (BC) and greater near-residence traffic density in mid-childhood had greater problems with behavioral regulation as assessed by classroom teachers. Investigators from the Harvard Clean Air Research Center examined the association between BC and PM2.5 and scores of the Behavior Rating Inventory of Executive Function (BRIEF) and the Strengths and Difficulties Questionnaire (SDQ), administered by parents and teachers of 1212 children in the project VIVA cohort, followed from before birth to a median age of 7.7. PM2.5 exposures were associated with scores, but not after controlling from covariates. Parent-administered scores were not associated with exposures. Prenatal and early childhood exposure to traffic-related pollution did not predict greater executive function or behavior problems, suggesting that mid-childhood may be a more sensitive exposure period for these effects. However, exposure to BC during the third trimester was associated with fewer problems of metacognition and behavioral problems. A nonlinear relationship between exposure and effects was observed, which might indicate a potential threshold for adverse neurodevelopmental effects around 0.5 μg/m3 ambient BC concentration