Not long after administrators learned a group of teens at Albany High School had been giving each other Nazi salutes in the halls and making racist posts on social media, anti-Semitic incidents spread to Piedmont High School, prompting an assembly and letter to parents this week.

“There was an incident with kids forming a swastika as part of a dance routine. There have been German words and salutes in the hallways, swastika graffiti and stuff,” said Rabbi Mark Bloom, whose son is a junior at Piedmont High.

The incidents — which also included racial slurs, anti-Semitic slurs and offensive gestures — had been happening for several months and were brought to the attention of school officials on April 24, according to an email sent to parents Monday.

At a school-wide assembly that day, four students read letters about how prejudice and bullying had affected them and their peers, with each letter centered around the theme of a particular type of bigotry, exploring prejudice against black, Asian, Jewish and LGBTQ students, Piedmont Unified School District Superintendent Randall Booker told The Chronicle on Thursday.

He added that he thought the students at the school had been moved by the assembly, which was intended to be “by students, for students.”

“You could literally hear a pin drop in the gym. And that’s a testament to the real culture at Piedmont High School,” Booker said.

The recent incidents involved a group of fewer than ten students, and they were disciplined with suspensions, according to Booker.

Bloom said he sees the problems as part of a bigger trend.

“There’s definitely an uptick, nationally and locally,” he said of anti-Semitic incidents. “It’s everywhere and it’s really disconcerting.”

“It’s definitely affecting teens more than it ever has. Ten years ago, maybe even five years ago, I’d ask confirmation classes of tenth graders, have any of you ever experienced anything [anti-Semitic] personally, and the answer was usually no. Today, the answer is usually yes,” he continued.

Booker said that over his 15 years working in the school district, the Internet has created new challenges.

“There’s so much unfiltered information available at the push of a button,” he said. “That’s what has changed the most.”

Some former students weren’t surprised to hear of the recent upheaval.

“I saw racist graffiti in the bathrooms, knew kids who were too afraid to come out as queer, heard too many anti-Semitic remarks played off as jokes,” one recent graduate observed on Facebook. “Instances like this are absolutely NOT new here.”

Bloom doesn’t think the students involved are earnest neo-Nazis, and suspects the incidents stem from kids making insensitive jokes fueled by social media and Internet culture. He praised the school district’s handling of the situation.

“I think they’re trying very hard and actually doing a good job — but they’re obviously going to have to do more to solve it,” he said. “But I have no idea what that is.”

School districts face pressure from all sides in dealing with hate incidents. At Albany High School, several students were suspended in connection with a racist Instagram account, and their return to school was protested by their peers, who staged a sit-in. Four of the students who were suspected are now suing the school district, charging they were wrongly disciplined and that their First Amendment rights were infringed.

Piedmont High School is launching a new tool, the Highlander Hotline, allowing students to easily report abuse and bullying online, Booker said. With the school year in its final weeks, administrators are meeting intensively with students and are working with police and community groups to devise a strategy for the fall.

“We’ve worked for years making the number one priority the social and emotional health of our students,” he said.

Filipa Ioannou is a San Francisco Chronicle staff writer. Email: fioannou@sfchronicle.com Twitter: @obioannoukenobi