A pupil at secondary school near the German city of Dortmund has been killed by a fellow classmate, according to police.
Reports say a 15-year-old student stabbed a 14-year-old boy.
The attack happened at around 08:00 local time (07:00 GMT) at the Käthe Kollwitz comprehensive school in the town of Lünen.
One teenager has been arrested on suspicion of murder. Pastors are at the school to support pupils and parents.
Police say they are investigating and have not released any further details.
German media say both the victim and the suspect are German citizens, while the latter also has a Kazakh passport.
Officials in North Rhine-Westphalia have recently vowed to tackle the problem of youth violence in Germany’s most populous state.
According to police, one in five offenders in 2016 was under 21.