Reducing air pollution levels could boost children's working memory by 6%, the equivalent of four extra weeks of learning time per year, research suggests.
Modelling by the University of Manchester found that a reduction of 20% in air pollution levels in and around school grounds can improve a child's learning ability by 6.1%.
The research, carried out on behalf of charity Global Action Plan, suggests up to 500,000 children may be being exposed to harmful levels of air pollution.
The findings are part of a year-long research project conducted by the Clean Air for Schools Programme and have been released as part of Clean Air Day 2020.
The project looked at how air pollution affects children in schools across the UK and Ireland, and includes additional research from 19 schools totalling approximately 6,000 students across Greater Manchester.
Professor Martie van Tongeren, professor in occupational and environmental health at the University of Manchester, said that improving local air quality should be a priority.
"Pollution of indoor and outdoor air affects the health of our children," he said.
"The available evidence indicates that it affects their cognitive development, which may affect educational attainment.
"Studies that investigate the link between exposure to air pollution during early life and effects of educational attainment and brain health at later life are urgently needed and policies should be set out by ministers to tackle this urgent challenge, immediately."
Global Action Plan says up to 2,000 schools and nurseries are close to roads with levels of air pollution above the baseline level used in the model, meaning at least 500,000 children are exposed to levels of pollution that could affect their working memory.
Chris Large, co-chief executive of Global Action Plan, said:
"This year-long research project has uncovered the effects air pollution has on our children's ability to learn, as well as their health.
"Given lockdown restrictions have already impeded learning time, we must give all children a fighting chance, especially those in pollution hotspots who are also likely to be victims of the attainment gap."
It comes as air quality data by the Department for Environment, Food and Rural Affairs (Defra) shows that air pollution decreased by up to 40% on average across the UK in peak national lockdown during April and May 2020 compared with the same time last year.
Global Action Plan says it is viable to maintain a 20% reduction around school grounds through actions included in the Clean Air for Schools Framework.
Steve Marsland, head teacher at Russell Scott Primary School in Denton, Manchester, said: "Until the University of Manchester surveyed the air quality prior to the project we had no idea how poor the air quality was.
"Our school is in a particularly polluted area because of the numbers of roads, retail park and two motorways running past us that you almost accept that this is your lot and you learn to live with it.
"The Clean Air Project has proven that we don't have to live with it."
A spokesman for Defra said: "We know that air pollution is a major public health risk and poses the single greatest environmental risk to human health.
"That's why we are continuing to take urgent action to curb the impact air pollution has on communities across England through our ambitious Clean Air Strategy and the delivery of our £3.8 billion plan to clean up transport and tackle NO2 pollution.
"We work closely with Public Health England and advisory bodies such as the Committee on the Medical Effects of Air Pollutants and the Air Quality Expert Group to keep abreast of research on the impact of air pollution on public health.
"However, further research is needed to fully understand any links between air quality and children's cognitive development."