Robbers are targeting Oak Cliff students leaving school in the afternoons.

Three students were robbed outside of L.V. Stockard Middle School on Friday afternoon, according to a parent who posted about it on Facebook. In that case, a man pulled up in a black Chevy Impala with tinted windows and demanded their phones at gunpoint.

Dallas ISD told the parent this wasn’t an isolated incident, and the district sent out a letter warning parents of a series of robberies targeting students walking alone or waiting at bus stops.

The letter encourages students to stay in groups, avoid dimly lit areas and keep their cellphones out of sight.