Young people with masks or scarves covering up their faces storm buildings, attempting to plant posters and flags with vulgar slogans that announce their dominance. Boys and girls lie on the ground, bleeding, while police try to get a handle on the situation. This is how Cologne students celebrated the end of their high school career in 2016.

Originally, the prom wars were an extension of graduation pranks, a last hurrah of sorts for graduating students. For several years, they have used social networks to arrange the prank attacks on rival schools. The students of the targeted schools play the role of defenders, using water pistols and paint balloons.

On YouTube, various student groups have posted videos in preparation for the "prom wars" that show them waving their school's flags. While the tone of the short films is rather martial, the official message is not.

One video posted by student's of Cologne's Hansa School comes with the call for a "fair, non-violent 'Abikrieg' without any material damage."

It was published on March 12, the weekend before events spiraled out of control.

"This time of year is a transition period for graduating students, the last week in their familiar environment before the great unknown begins," explained Katrin Bauer, a cultural scientist at the LVR Museum for Applied Geography and Regional History.

Bauer wrote her master's thesis on German graduation pranks and told DW that it's not unusual that graduating students strongly align themselves with their schools before they leave their friends and familiar environment behind. But hospitalized students and police investigations spell a new level of escalation, Bauer said.

One student could go blind

Over the past years, the "Abikrieg" confrontations have turned more and more violent with teachers and police calling on the students to exercise restraint.

One student who was part of the "Abikrieg" in 2013 said there were troublemakers in his year as well.

"I realized that other schools were taking it way too seriously," the student, who wanted to remain anonymous, told DW. "In our video, we were aiming bananas and cucumbers at the camera. They were using air-guns or stun pistols. That's a huge difference in my opinion."

This year, two students suffered serious head injuries on the night between Monday and Tuesday, when a large group tried to storm Humboldt High School in Cologne. Some 200 hundred students were involved in the clash, according to police.

"The injuries of the victims indicate that firecrackers and bottles were thrown," said Cologne police spokesman Dirk Weber.

One of the victims was treated for skull fracture; the other suffered a face injury. According to media reports, he could go permanently blind. Both of them are 18 years old.

The police also seized drugs, baseball bats and a bike chain, all allegedly used by students in previous days.

Violent individuals, not a dangerous mob

A group of students who said they were from the Humboldt school denounced the violence on social media.

"We, the 12-graders of Humboldt, hereby end the 'prom-war,'" they wrote. "This has gone way too far. We were pelted with glass bottles, firecrackers, eggs and stones."

The statement also stressed that the "prom war" tradition has been hijacked by violent individuals who were looking for a fight.

Criticism from other social media users, however, does not distinguish between individuals. All over Germany, people are voicing their shock and anger about the Cologne events.

"The 'Abikrieg' should really prompt us to discuss our education system," this Twitter user wrote, calling the events "sad and embarrassing."

The 2013 graduate DW spoke to doesn't see anything wrong with 200 students blowing off steam in a water fight. But he also says that "some idiots abuse these moments to live out their aggressive fantasies."

"You either have to make sure that everyone is very clear about the rules, or you have to end this tradition altogether."

Cologne-specific problem

Graduating students in Germany usually dress up for different themes every day for the last week of school: "Hollywood-Style" on Monday, mafia boss suits on Thursday and a big party during school hours with too much alcohol on Friday. The worst thing that happened in this reporter's graduating class in northern Germany was an indoor-smoking controversy - in the end, the class had to pay for the auditorium's floors to be renewed. Aside from some bad hangovers, no one got hurt.

Bauer: Violence is the exception, not the rule

Soon-to-be graduates are looking forward to the end of high school everywhere, but Cologne seems to be the only city where violence broke out, said Katrin Bauer. One possible reason is the large number of high schools in a relatively small area.

Just a few student generations ago, big celebrations didn't take place at all. In the 1960s, German graduates were simply sent their high school diplomas in the mail and there usually weren't any big, student-organized events surrounding graduation. The '70s and '80s saw the first small pranks.

"It was in the '90s that things got more expensive, more professional," Bauer said about the graduation shenanigans. Students started organizing theme weeks and parties, and lining up sponsors for prom dances in fancy hotels.

Diplomas not in peril

Whether students who fought in the Cologne "Abi-Krieg" this year will have a prom remains to be seen. Cancelling such a popular event is one of the few immediate consequences school officials can impose.

No student can be excluded from final exams for reasons that aren't directly related to in-class instruction or the student's grades. That means that all students on track to graduate this year will do so, "prom wars" notwithstanding. But they might have to go to court and could end up with a criminal record.