Study objective: To examine the effects of chronic exposure to aircraft noise on children's school performance taking into account social class and school characteristics. Design: This is a cross sectional study using the National Standardised Scores (SATs) in mathematics, science, and English (11 000 scores from children aged 11 years). The analyses used multilevel modelling to determine the effects of chronic aircraft noise exposure on childrens' school performance adjusting for demographic, socioeconomic and school factors in 123 primary schools around Heathrow Airport. Schools were assigned aircraft noise exposure level from the 1994 Civil Aviation Authority aircraft noise contour maps. Setting: Primary schools. Participants: The sample were approximately 11 000 children in year 6 (approximately 11 years old) from 123 schools in the three boroughs surrounding Heathrow Airport. Main results: Chronic exposure to aircraft noise was significantly related to poorer reading and mathematics performance. After adjustment for the average socioeconomic status of the school intake (measured by percentage of pupils eligible for free school meals) these associations were no longer statistically significant. Conclusions: Chronic exposure to aircraft noise is associated with school performance in reading and mathematics in a dose-response function but this association is confounded by socioeconomic factors. P revious studies examining the association between chronic noise exposure at school and at home, or both, with standardised reading and other intellectual achievement tests have found preliminary evidence of a relation between environmental noise exposure and school performance.1-6 Green and colleagues, 7 in the most comprehensive study to date, analysing a large database of school achievement tests, studied 8240 grades from children in years 2-6 of 362 schools (geo-coded into five aircraft noise bands) around airports in New York City. They found a dose-response relation that indicated that the percentage reading below grade level increased as noise level increased. Two limitations of this study will be addressed in the present study. Firstly, the reading outcome was a dichotomous variable (above/below grade level), which is not as sensitive as a continuous performance measure taken at the individual level. Secondly, the performance outcomes in the analysis did not take account of the clustered nature of the data by using performance scores at the individual level.The results of previous studies examining the effects of aircraft noise on child cognitive performance raise further questions, two of which will be addressed in this study. Firstly, were associations found previously confounded by social class and school characteristics?It is possible that previous noise effects may be confounded by school effects and by social deprivation. 8 9 A school effect means that the characteristics of individual schools may have a more powerful effect than noise exposure on school performance. School quality and social deprivation ...