A student in Puerto Vallarta, Mexico, in February.

A Taliban security officer using a mobile phone in Kandahar, Afghanistan, last year. Civil servants and members of the country’s armed forces have been told not to bring smartphones to work.

The mother of Jimmy, 12, said she tried to build relationships with families that share her concerns about social media and to nurture his interests in activities that don’t involve screens.

Using a smartphone in Sydney, Australia, last year. In December, the country banned social media for those under 16.

People exchanging World Cup stickers in Buenos Aires last month.

A teenager using a smartphone in Vienna. Some participants in a phone ban experiment felt more connected to their families and hobbies, while others struggled without the instant digital stimulus.