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Every kid hates the school bus. The seats are uncomfortable, the ride is jarring, the bus driver is probably a closet fascist based on the way he so relishes screaming, every other kid on the bus is kind of a jerk, and the back of the bus reeks of fumes. Turns out, those fumes, or at least the general pollution that comes from old diesel engines, may have a significant impact on children’s health and their academic performance.

At least, those are the findings of a recent study conducted by Georgia State University researchers who looked at a decade of test scores in Georgia and compared the results to which school districts retrofitted their school buses to reduce emissions by up to 95 percent.

The results: emission-reducing retrofits are correlated with higher English scores, but only marginally improved math scores. The study says the academic improvements are about equivalent to replacing a first-year teacher with a five-year veteran.

You may be reading this and thinking this is a blatant case of correlation does not equal causation. But, in a blog post for the Brookings Institution website, the authors address this concern:

One might worry that districts that retrofit buses are different in some way than those that do not. For example, they may care more about student health—and implement other initiatives, perhaps unrelated to buses, that improve health. Our research design dealt with this in two ways. First, by observing changes across districts over time we removed anything about districts that doesn’t vary over time, like preferences for health or general teaching quality. Second, we employed a placebo test by also checking for changes in students’ body mass index (BMI). If retrofitting districts were just getting healthier anyway, we would also see changes in BMI. We wouldn’t, however, expect bus retrofits to directly affect BMI.

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Despite strong outcomes with test scores and health performance, the authors didn’t find any effect on BMI, supporting the link between school bus emissions and academic outcomes.

Further, because different districts retrofitted varying percentages of their bus fleets—some retrofitted 10 percent, others half, and still more didn’t retrofit any at all—it provided another robustness test for evaluating how much of the effects they saw were due to the bus emissions issue.

Georgia, like most states, underwent numerous changes to their standardized testing protocols from 2007 to 2017, the time frame studied, including a notorious cheating scandal. But Daniel Kreisman, one of the study’s authors, told Jalopnik via email that this wouldn’t have impacted the results because they used a model that removed any year-specific effects, such as a new test.

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“Another way to think about this is that we’re comparing retrofitting districts’ relative performance on the test to non-retrofitting districts,” Kriesman wrote. “Whether the test changes simply means that we’re comparing across these districts on a (slightly) different test.”

Pollution resulting in lower test scores or worse health for children is hardly a shocking finding. In fact, a separate study found that students in schools near highways and other major streets with higher traffic pollution also experience drops in test scores along with more absences and behavioral issues.

The good news is retrofitting buses is not particularly expensive, especially when compared to other methods of increasing test scores or making children healthier. The authors note that the cost of retrofitting 10 percent of the average district’s bus fleet amounts to a mere $90,000. Georgia’s 2020 budget for K-12 public schools is $10.6 billion.

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It shouldn’t take a rigorous cost-benefit calculus to determine it’s actually good to stop poisoning our children with diesel fumes, but here we are.