A year seven student gave the Nazi salute to taunt one of his classmates amid a series of anti-Semitic incidents at an inner west high school.

Two students were suspended after a teacher witnessed the incident at the Balmain campus of Sydney Secondary College, a state high school, early last week, the Herald has learned.

But the anti-Semitic bullying had gone on for at least a month before then.

The parents of 18 year seven students - both the bullies and their victims - were contacted during the investigation sparked by the June 25 incident.

Most of the harassment is understood to have been propagated by the two ringleaders, who were suspended.