It is a question that keeps some parents awake at night. Should children be allowed to take mobile phones to school?
Now economists claim to have an answer. For parents who want to boost their children's academic prospects, it is no.
The effect of banning mobile phones from school premises adds up to the equivalent of an extra week's schooling over a pupil's academic year, according to research by Louis-Philippe Beland and Richard Murphy, published by the Centre for Economic Performance at the London School of Economics.
"Ill Communication: The Impact of Mobile Phones on Student Performance" found that after schools banned mobile phones, the test scores of students aged 16 improved by 6.4 per cent. The economists reckon this is the "equivalent of adding five days to the school year".
The findings will feed the debate about children's access to mobile phones. In the UK, more than 90 per cent of teenagers own a mobile phone; in the US, just under three quarters have one. Head teachers' attitude towards the technology has hardened as it has become ubiquitous.
In a survey conducted in 2001, no school banned mobiles. By 2007, this had risen to 50 per cent, and by 2012 98 per cent of schools either did not allow phones on school premises or required them to be handed in at the beginning of the day.
However, some schools are starting to allow limited use of the devices. New York mayor Bill de Blasio has lifted a 10-year ban on phones on school premises, with the city's chancellor of schools stating it would reduce inequality.
This view is misguided, say the researchers. They found the ban improved test scores among students, with the lowest-achieving students gaining twice as much as average students.