Pupils from secondary schools have been told not to wear their blazers while walking home due to the risk of planned “disorder” between children from different schools.
Essex Police said teenagers had been using social media to organise anti-social behaviour in the south of the county.
Genevieve Mullen, a parent who is also a BBC producer, said her son was sent home with a letter outlining the action police had taken to try to prevent any violence.
“It’s worrying to receive a letter like that and to hear that your children have been [specifically] told not to bring in weapons to school,” she said.