'Schools should have consistent policy on phones'
Pupils in schools where smartphones are banned like being free of the associated pressures, says England's Children's Commissioner Anne Longfield.
Ms Longfield said schools across England should have a consistent approach to the use of mobile phones.
She told the Commons Science and Technology Committee that every school seemed to have its own policy on whether pupils could use phones.
She said schools could help families if they took a "bold approach".
The select committee was taking evidence about the impact of social media and screen use on young people's health.
Appearing as a witness on Tuesday, Ms Longfield said research from her office had shown that children's social media use increased dramatically when they made the transition between primary and secondary school.
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She said children spoke to her about an "avalanche of pressure", particularly in the first year of secondary school, to be popular and successful on social media.
"The huge message for me out of that was to prepare children in Year 6, at primary school.
"I've seen some really good examples where you've got secondary-school-age children going back to primary schools and saying, 'If I'd have known this, then this would have really helped', and I think the peer education is a really important part of the whole solution as well."
'Every school has its own policy'
Ms Longfield said schools took very different approaches over the use of smartphones during the school day.
"Every school is different, every school will have some kind of policy.
"Some of it is, 'Keep it in your bag if you can', some are quite off-hand with it, some say, 'No smartphones in school', but they allow the old brick phones in, you know, a little £10 phone so you can make phones calls.
"But I've been to schools where they don't even allow that during school time.
"There's a school in north London that does this and the children I spoke to - they worked with teachers and worked with parents on this - actually like that time in school where they don't have those pressures.
"I would like there to be a commitment that there is consistency across schools in that it isn't relying on the will of the school or the interests of the school."
She added: "It couldn't be something you could impose without being able to bring people with you to really make it effective, but I think there's a real role here for school to be brave and bold and have that leadership with families about access to screens in schools."