This video was taken by a cell phone and posted by one of the students. It was later posted on Dutch website GeenStijl.
The ugly event took place in a classroom where most pupils have a foreign Third world background. Some of them do not even speak Dutch. The fact the teacher has a broken arm did not make any difference for the African pupil (Refugee? Asylum seeker?) to trash the poor teacher over and over again. His friends in the background encouraged the offender in Arabic to finish him.
In the neighbouring classroom we see through the glass partition two persons who are not doing the slightest effort to help the poor man.
Via Vlad Tepes: