Exposure to high levels of aircraft noise may affect children's reading skills, researchers claim.
Many children were also exposed to aircraft noise at home
A team from Barts and the London NHS Trust looked at data on more than 2,800 children living near Heathrow and other airports in Spain and the Netherlands.
The Lancet study found each five decibel increase in noise level was linked to children being up to two months behind in their reading age.
A US expert said the study supported previous research findings.
The children, all aged nine or 10, attended schools near to London's Heathrow Airport, Schiphol in the Netherlands and Barajas in Spain.
But the researchers said their findings applied to the area around any airport.
Exposure to aircraft noise was associated with impaired reading comprehension, even after factors such as socio-economic differences between schools were taken into account.
Reading age was delayed by up to two months per five decibel increase in noise levels in the UK children studied, who attended schools in the boroughs of Hounslow, Hillingdon and Slough, and up to one month in the Dutch children.
A similar comparison could not be made for the Spanish children studied as there is no national data on reading age available.
Long term effects 'unknown'
Overall, the researchers found a difference of around 20 decibels between children exposed to the lowest and highest levels of aircraft noise.
This translates to a delay of up to eight months in a child's expected reading age.
The researchers say that while this is significant, it is much lower than the two year reading age delay seen in children with learning difficulties.
They suggest that children exposed to noise learn to tune it out - but this can mean they also tune out other external noise, such as teacher's instructions.
Increased levels of exposure to both aircraft and traffic noise was associated with additional stress in children and a reduced quality of life.
However, exposure to traffic noise alone did not have an effect on reading age and, unexpectedly, was found to improve recall in memory tests.
Professor Stephen Stansfeld, who led the research, said: "These exposure-effect associations, in combination with results from earlier studies, suggest a causal effect of exposure to aircraft noise on children's reading comprehension.
"In practical terms, aircraft noise might only have a small effect on the development of reading, but the effect of long-term exposure remains unknown."
He said the results were relevant to the design and placement of schools in relation to airports and to the formulation of policy on noise and child health as well as the wider consideration of the effect of environmental factors on children's development.
Schools which already existed near to airports should be properly insulated to give children as much protection as possible from the effects of aircraft noise, said the researchers.
Writing in the Lancet, Dr Peter Rabinowitz of Yale University School of Medicine, said this latest research backed up previous analyses.
He highlighted one study which looked at children living near to the old Munich airport in Germany, before and after it was closed down.
"Children attending schools near the airport improved their reading scores and cognitive memory performance as the airport shut down, while children going to school near the new airport experienced a decline in testing scores."
The London Borough of Hounslow said that, in light of the research, it had launched an investigation into the impact of aircraft noise on local schools.