Educational Benefits of Reducing Lead Exposure

Click here for a larger version the graph.

The Issue:

It can be difficult to trace a link between improving environmental quality and improving children’s educational outcomes. Poor environmental quality tends to be more prevalent in lower-income, minority neighborhoods, which complicates disentangling the impact of pollution from other factors associated with poverty. However, the switch from leaded to unleaded fuel by a major automotive racing organization, the National Association for Stock Car Auto Racing (NASCAR), provided a natural experiment to isolate the impact of an environmental factor on learning. In our research we measure how reducing airborne lead exposure improved children’s test scores at schools located near NASCAR race tracks. The results highlight the importance of environmental quality as an input to education — as well as the benefits of reducing lead exposure, even in locations with comparatively low levels of existing contamination.

Even small amounts of lead exposure, repeated over time, can have large and economically significant effects on student outcomes.

The Facts:

• Lead poisoning can have large negative effects across all ages. Higher lead exposure as adults can cause increased mortality and decreased fertility. Early-life exposure can lead to lasting consequences for impacted children, including neurological damage, increased impulsiveness and self-control problems linked to criminal behavior, and hindered learning. 
• Although the use of leaded fuel has been largely abolished in the United States, exceptions remain. Despite early evidence of lead’s harmful effects, leaded gasoline was common in the early years of personal automotive transport. Since then, countries around the world have banned the sale of leaded gasoline for on-road automotive use. However, the phaseout of lead from gasoline is incomplete. In the United States, and in many other countries, the use of leaded gasoline continues in piston-engine aircraft and automotive racing, among other uses. 
• Races using leaded fuel emit large quantities of lead causing detectable changes in ambient air concentrations. Prior to shifting away from leaded fuel, a single three-hour NASCAR race emitted as much lead as the average airport does in an entire year. Jointly, all the NASCAR races in a year would emit an estimated 2 million grams of lead, accounting for roughly 0.5% of all annual U.S. lead emissions (see here). Starting in 2007, NASCAR switched from leaded to unleaded fuel, generating a permanent and detectable decrease in nearby ambient lead concentrations. This lowered the rates of measured lead poisoning in children living within 50 miles of racetracks. 
• In our recent paper, we study the causal effect of early life lead exposure on children’s education, using scores on Florida mathematics and reading tests for grades 3-5 as our measure of learning. Since the fuel change happened independently of any changes in economic, demographic, or other such factors that might impact children’s academic achievements (such as trends in socioeconomic status, nutrition, and school characteristics), the policy shift allows us to explore the causal effect of lead exposure without bias from such confounding issues.
• Higher levels of lead exposure reduced academic performance for elementary school children. We see that average test scores for schools closer to racetracks improved relative to their counterparts farther-away after NASCAR shifted away from leaded fuel (see chart). While test score trends were similar earlier on, after deleading, test scores increased for the average 3rd-5th grader going to school near a racetrack by 0.079 standard deviations, and the likelihood of achieving the state standard for proficiency rose by 2.221 percentage points, with the largest improvements happening in math scores. 
• Duration of exposure matters, and even small exposures can add up over time. We find that, for a given amount of lead exposure, damages appear greater when exposure occurs over an extended time – multiple small doses may be just as bad, if not worse, than a large, one-time hit. The children exposed to leaded races for more years had lower test scores than children whose exposure was shorter — even if the total accrued amount of lead to which they were exposed was the same. This may be due to key stages of development occurring throughout childhood. Development of working memory is largely linear up to around age 13, and the abilities to process multiple sources of information and efficiently tackle defined tasks have a critical development stage closer to ages 7 through 9. Being exposed to lead during multiple crucial development stages may lead to worse outcomes.
• The negative effects of lead on learning impact students at all levels of achievement. We find the average lifetime NASCAR lead exposure for schools closer to racetracks reduces the school-level share of students in the highest test score achievement levels by just under 1 percentage point each, and increases the share of students in the lowest achievement levels by about 1 percentage points each, indicating an overall shift from higher to lower achievement levels. Negative effects are larger in counties that have a higher share of residents that are black and counties with a higher poverty rate, suggesting lead exposure is an environmental justice issue. 
• The benefits of reducing lead exposure are large and comparable to the educational benefits from making substantial improvements in school-based inputs such as teacher quality or class size. For students at schools that are located 1 mile away from a racetrack, removing the average NASCAR lead exposure had an effect comparable to reducing class size by 3 students; increasing school spending per pupil by $750; or 25% of the effect of avoiding an instructor with no previous teaching experience. By converting test scores into expected changes in lifetime earnings, we find that the average affected third grader gained 0.92% in lifetime earnings, a present value of $5,200 over their lives (calculations based on findings from this research).