The chief inspector of Ofsted is backing head teachers who ban mobile phones to prevent bad behaviour.
In a speech, Amanda Spielman is expected to blame technology for making "low-level disruption" more common and endorse tough behaviour policies.
"The place of mobile phones in the classroom seems to me dubious at best," she will say.
Her speech comes after Culture Secretary Matt Hancock also called on head teachers to ban phones.
Ms Spielman is due to tell the audience at the Festival of Education at Wellington College that it was "entirely appropriate" for schools to use sanctions such as writing lines, detention or "community service" punishments such as picking up litter.
She will say: "I fundamentally disagree with those who say that taking a tough stance on behaviour is unfair to children.
"Quite the opposite, there is nothing kind about letting a few pupils spoil school for everyone else."
Her speech says that the educational benefits of mobile phones are unproven, but they do distract pupils in class and make teachers' jobs harder.
"There's no doubt that technology has made the challenge of low-level disruption even worse, which is why I also support recent calls to back heads who have decided that the way to improve behaviour is to ban mobile phones in their schools," Ms Spielman will say.
"I'm not the target audience, but nevertheless I am yet to be convinced of the educational benefits of all-day access to Snapchat and the like."
Ms Spielman will say that she wants Ofsted to respond to the importance that parents attach to behaviour by giving it a prominent place in inspection reports.
"I want to see behaviour get the attention it deserves in our inspections, probably through a separate behaviour and attitudes judgement," she will say.
Hidden from inspectors
Low-level disruption which gets in the way of pupils' learning will be taken as seriously as incidents such as bullying, she will pledge.
The chief inspector's speech also says that Ofsted will examine whether schools are trying to conceal badly behaved students during inspections to get a better grade.
"I want to address once and for all, the constant rumours we hear about badly behaved children being hidden from inspectors, perhaps on conveniently timed school trips," she will say.
Ofsted's research and analysis teams are devising a way to assess how often such incidents happen and how inspectors can respond.
According to the Department for Education, 95% of schools now control the use of mobile phones in some way.
Some schools insist that they are kept switched off and out of sight during the whole school day, others restrict their use to break time and some allow them to be used in lessons for specific educational activities.
A Snapchat spokesman said parents and teachers should have regular conversations about the appropriate use of technology, including the company's app.
He said: "We don't recommend that young people use it all day while at school."