By Pat Hagan

A study of almost 2,000 pupils at schools in southern California showed some were up to four times more likely to miss classes due to respiratory illness than those from smoke-free homes.

The finding comes just days after the British Medical Journal published a controversial paper questioning the risks of passive smoking.

Anti-smoking groups reacted angrily to the publication of the BMJ study - partly funded by the tobacco industry - which suggested the link with heart disease and lung cancer was considerably weaker than thought.

A spokesman for the charity Action on Smoking and Health told the BBC the latest research confirmed the social as well as physical damage that passive smoking causes.

"It does not surprise us at all that it affects not only children's health but their development as well," said researcher Naj Dehlavi.

"We already know that around 17,000 children a year under the age of five end up being hospitalised with problems like glue ear or respiratory complications as a direct result of passive smoking."

Little research

Although the impact on the health of young children is well known, little research has been carried out to see if their education is affected too.

Researchers from the Keck School of Medicine at the University of Southern California studied 1,932 fourth grade pupils and questioned each one on whether their parents or other family members smoked.

Records were then examined to see which children had been off school with chest problems in the previous six months.

The results, published in the American Journal of Epidemiology, showed kids from smoking homes were at least 27 per cent more likely to have been off sick.

The risks rose considerably if there was more than one smoker and if the child had a history of asthma.

For example, asthmatic pupils with two or smokers at home were four times more likely to need time off than healthy youngsters whose parents were non-smokers.

Dr Frank Gilliland, who led the research, said: "Environmental tobacco smoke exposure is associated with increased respiratory-related school absenteeism among children, especially those with asthma."

A spokeswoman for the UK's National Asthma Campaign said other studies showed the incidence of asthma is increased by 60 per cent in children of smokers in the UK.

She added: "We would encourage any parent whose child has asthma to keep them away from smoky atmospheres as this can be harmful to growing lungs."