Thirteen suspensions were handed out at Calgary's St. Francis High School. (CBC)

Thirteen high school students in Calgary have been suspended after a red-headed teen was beaten because of the colour of his hair.

The Grade 10 boy was attacked in the locker room of St. Francis High School after gym class Thursday, students told CBC News.

The victim was taken to hospital for examination, and a spokeswoman for the Calgary Catholic School District said Friday he sustained "some minor bruising" to his upper body.

Calgary police are looking into the assault as a possible hate crime.

"The fact of the matter is from a policing perspective, it is a hate crime, and this individual was targeted because of the fact they have red hair," said police spokesman Kevin Brookwell.

CBC News has also learned that two red-haired, Grade 7 girls at St. Alphonsus Elementary/Junior High School were swarmed and kicked repeatedly by older girls on Thursday. Board spokeswoman Janet Sutherland said two students have been suspended in that case.

The attacks came on a day promoted by a Facebook group as Kick a Ginger Day. The Facebook group urged members to kick people with red hair — referred to as ginger kids — on Nov. 20.

The phenomenon appears to be linked to South Park, an animated TV show. An episode of the satirical show that originally aired in 2005 dealt with one character's mindless prejudice against red-haired people.

One student admitted kicking red-haired friends at school as a joke but says things went too far. (CBC)

Calgary police said they were aware of the campaign but decided not to issue any warnings.

"We didn't want to bring any more profile to this campaign to the city or the students and so the decision was that we would just see what happened," said Brookwell.

Ken Logel, a Grade 12 student at the northwest St. Francis High School, admitted kicking some classmates had been a running joke all day.

"I have a few buddies with red hair. You just kind of kick them lightly just as a joke. But when it gets carried way, that's not cool," he said Friday.

His friend, Simon Burke, added: "Some kids took it too far in the locker room yesterday and ended up really hurting one of the kids at our school. It's really hard to hear about it and I'm pretty disappointed in the kids that did it.

"Mostly, kids at the school are pretty good people and don't really expect people to be hurting other ones just for having red hair. It's just pretty ridiculous."

The high school is also investigating.

"From what I understand, he was targeted based on the colour of his hair," said Sutherland. "Regardless of why the incident happened, I think it's important to note that violence in school is never tolerated."

This week, schools in Manitoba and Newfoundland and Labrador sent warnings to students and parents about the prank.

Twenty students from a Vancouver Island middle school were sent home Thursday after they kicked red-haired schoolmates.

With files from Peter Akman