A row over sexting has erupted after a minister called for teachers to look through pupils' mobile phones to delete sexual photos.
Norman Baker, a Home Office minister, said young people had to be taught about the risks of sending intimate photographs of themselves by text, email or instant messaging.
He told the House of Commons: "We have given teachers stronger powers to tackle cyber-bullying by searching for and, if necessary, deleting inappropriate images or files on electronic devices, including mobile phones.
"It is critical to educate young people about the risks of sending intimate photographs."
However, unions said it was not the job of teachers to police the contents of pupils' devices.
Chris Keates, General Secretary of the NASUWT, said: "It is completely inappropriate for teachers to be placed in the position of 'policing' pupils' phones.
"Schools can make a valuable and important contribution to advising pupils on how to keep safe when using the internet and social media but it is not teachers' responsibility to scrutinise and censor phones."
The Internet Watch Foundation revealed last year that as well as being shared on teens' smartphones, tens of thousands of explicit selfies taken by teenagers are ending up on websites viewed by paedophiles.
Children's charity ChildLine also warns that young people are taking huge risks by taking and sending the sexual images.
Some are being driven to the brink of suicide when photos sent to one person they think they can trust become widely shared online.
Tory MP Sarah Wollaston called for the government to go further and ban children from using smartphones altogether if they are caught using sexting images to bully other pupils.
She said: "Many young people have been pressured into sending intimate photographs of themselves only to find that those images are sometimes posted, distributed or shared without their consent, which is an important form of bullying and harassment."
She asked Mr Baker: "What measures have been taken, and do you support measures to prevent smart phone use by those who are not mature enough to understand that it can result in an important form of bullying?"
But Mr Baker insisted: "There are numerous laws in place that can be used to deal with those who behave in this appalling manner."
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