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Head teachers in England are more likely to face problems with pupils bullying online and misusing social media than in any other developed country, an international study says.
A report from the OECD think tank reported the experiences of more than 250,000 teachers in 48 industrialised countries and regions.
It showed particular problems with cyber-bullying in England's schools. The OECD's education director called for more regulation of social media, rather than leaving individual heads to try to cope.
The study, from the economics think tank the Teaching and Learning International Survey, looked at the working lives of teachers around the world, with England participating but not Scotland, Wales or Northern Ireland.
The survey, carried out every five years, indicated an increase in bullying in England's schools - driven by online bullying and harassment and problems caused by social media.
Of the heads in England surveyed:
In France, mobile phones have been banned from school - and the OECD education expert said education systems had to find a way of dealing with the impact of social media and internet use on young people.
He warned of a lack of regulation in England, which left schools having to find their own response.
For help with cyberbullying: