Banning phones in schools should be a decision for head teachers and not "imposed nationally by the government", England's children's commissioner has said.
Nine in ten secondary schools restrict the use of smartphones, according to a survey of 19,000 schools and colleges commissioned by Dame Rachel de Souza.
Dame Rachel said children were racking up hours of screen time at home instead, and that "the people with the real power here are the parents".
Her comments come as the general secretary of the UK's largest teaching union said a government ban on phones would "take the pressure off schools".