JFS, the largest Jewish school in Europe, has banned the use of mobile phones by students, saying it is concerned about the devices' impact on "mental health and well-being".
For 18 months, the school experimented with letting children to use phones in class as an educational tool at the discretion of teachers.
But a spokesman for the school said this had, in practice, led to wider use of phones.
Pupils will now have to store phones in lockers during the school day rather than keeping them on them.
The JFS spokesman said: “While we acknowledge the positive impact that technology can bring to society and specifically to learning environments, we are also aware of the deep and long-lasting effects of the excessive use of mobile devices can have on the mental health and well-being of children.”
The new policy was designed so technology “can be used responsibly by all”, he added.
In an email to parents, new headteacher Rachel Fink thanked them for their “overwhelming support”.
“I am confident that this change is in the best interests of our students both in terms of their learning experience and their wellbeing,” she said.
“It is interesting to note that students themselves are taking this seriously with conversations in the corridors about adapting to ‘life beyond my phone’!”
But she suggested there needed to be an effective deterrent, as many students needed help to persuade them to switch off their mobiles.
The school would continue to provide children with digital devices for educational use, the JFS spokesman said, but other devices should not be brought into school with the exception of those permitted for children with special needs.
He said JFS planned to introduce the policy before the chief inspector of Ofsted, Amanda Spielman, supported mobile bans.
“There’s no doubt that technology has made the challenge of low-level disruption even worse,” Mrs Spielman said in a recent speech.
“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; and the place of mobile phones in the classroom seems to me dubious at best.”
