BERLIN—Solomon Michalski loved going to his new school on a leafy Berlin street because it was vibrant and diverse, with most students from migrant families. But when the teenage grandson of Holocaust survivors let it slip that he was Jewish, former friends started hissing insults at him in class, he says. Last year some of them brandishing what looked like a gun took him aside and said they would execute him.

It was no isolated occurrence. The police registered 1,453 anti-Semitic incidents in Germany last year, more than...