How our new study concluded that London’s Low Emission Zone has improved the exam performance of school pupils

Sefi Roth explains the methods and results of a new study that concludes that air pollution regulations in the form of a Low Emission Zone have improved exam results in London at the end of Key Stage 2 and have the potential to significantly reduce educational disparities.

Last week co-authors and I published a new working paper that found the exam results of 11-year-old school pupils in London had improved as a result of the introduction in 2008 of the Low Emission Zone (LEZ). Our paper, Putting Low Emission Zones (LEZs) to the test: the effect of London’s LEZ on education, has attracted interest from the London Evening Standard, The Sunday Telegraph and other media. Here I provide a summary of our results.

There is already strong evidence that air pollution can have a wide range of impacts on children’s health and well-being, including damage to their attendance and performance at school. For instance, a study published earlier this year found that reducing the air pollution from power plants has increased nationwide test scores for school students in the United States.

Despite the well-documented link between LEZs and air pollution concentrations, and between air pollution and educational achievement, there has been no thorough evaluation of the effect of LEZs on standardised exam results.

The London LEZ was introduced in February 2008 to charge heavy diesel vehicles that did not meet minimum standards for emissions of particulate matter. The LEZ was expanded several times and now covers most of Greater London.

In our study, we examined the effect of the London LEZ on standardised Key Stage 2 results from tests on pupils at age 10 and 11, between 2005 and 2015. Our analysis showed a statistically and economically significant improvement in test scores for students located within the LEZ compared with those in a control group. Importantly, we also found that the LEZ policy has larger positive effects in low-performing schools, demonstrating its potential to significantly reduce educational disparities, and growing positive impacts over time.

We were able to go further than identifying a simple correlation to describe compelling evidence for a causal effect. We did this by using state of the art econometrics techniques to deal with possible confounding factors, such as the fact that London is inherently different to other cities.

Of particular importance is our use of a ‘difference-in-differences’ method that compared London with other large English cities before and after the establishment of the LEZ. In other words, we compared the differences in test scores between London and the other cities before and after the LEZ was established. This method relies on several assumptions, but the key one in our study is that, apart from the introduction of the LEZ, there were no other factors that were unaccounted for that changed the trend of academic performance in London compared with other cities following the introduction of the policy. We conducted several robustness tests to address such potential concerns as much as possible, including using a matching algorithm to select the control group (the other cities), and directly addressing the potential effects of the ‘Pupil Premium’ policy (grant funding to improve the educational outcomes of disadvantaged state sector pupils), which started in the 2011–12 school year.

Overall, we found robust evidence that there was a statistically significant difference in the improvement in test scores of pupils inside the LEZ compared with test scores of pupils in the other cities.

We also examined the impact on schools just outside the LEZ (within a 20 kilometre-wide buffer) and compared them with our control group. Our results show a relatively modest positive impact on the test scores of schools situated just outside the LEZ, which was less than one-third of the positive impact observed in the schools directly inside the LEZ boundary. However, this difference was not statistically significant.

There are several potential mechanisms that could explain the observed relationship between the implementation of the London LEZ and improved test scores. For example, previous studies show that reduced air pollution may directly enhance cognitive performance and cognition. Additionally, by lowering air pollution, LEZs likely reduce respiratory-related school absences, enabling students to attend more consistently, which can enhance academic performance. Future research should aim to provide clearer insights into the underlying mechanisms of this newly documented relationship between LEZs and educational outcomes.

Much of the work for this study was carried out by my co-author Antonio Avila-Uribe for his recently completed PhD, which was funded by the La Caixa Foundation in Spain. The paper was reviewed by two senior researchers at LSE and we are in the process of submitting it for publication in a leading economics journal. As the publication process for economics journals can take a long time, we have published our study as a working paper to inform other scholars and decision-makers who are interested in the impacts of LEZs on educational attainment.

Read the paper at www.lse.ac.uk/granthaminstitute/publication/putting-low-emission-zones-lezs-to-the-test-the-effect-of-londons-lez-on-education/.