SURREY, B.C. -- It happened back when she was in middle school.

It was a fundraising event during which students were bought and sold as "slaves," former student Layla Mohammed said.

The so-called "Slave Day" happened back in 2007 at Rosedale Traditional Middle School in Chilliwack, B.C., now called Rosedale Traditional Community School.

"The thing that really stands out most is remembering a specific teacher putting a leash and a collar on a student and walking them down the hallway, telling them to walk like a dog, crawl on the hallway floor while all the other students were laughing and making a mockery of it," Mohammed told CTV News Wednesday.

"At the time, it didn't mean much to me. I just thought it was strange," she said, adding she had supressed the incident in her mind for years.

Mohammed has been taking part in anti-racism rallies in Vancouver, and says she now understands just how wrong that school event was.

Another former student and friend of Mohammed says she also thinks it was wrong.

Cassie Robertson was one of the students who both bought slaves and was bought by others.

"It is showing us a sense of systemic racism that was taking place in my hometown, unfortunately, and it was something we didn't recognize at the time, but looking back now I see the issues with it and it was not OK," Robertson said.

"It just leaves me absolutely gutted. I had no idea anyone at our school could feel that way about this and that shows my own ignorance. And I feel extremely sorry for any the students that feel any disrespect," Robertson said.

"I really extend my apologies to Layla and any of the other students because I was part of the leadership that put that on at the time."

The now-principal of the middle school has posted an apology on the school website.

"We acknowledge that this did take place. We also acknowledge that it was wrong. I want to reassure our community that this event no longer takes place and has not for some time," wrote Paula Joran, principal at Rosedale Traditional Community.

The Chilliwack school board's superintendent, Rohan Arul-pragasam, has also issued an apology, saying slave day "is wrong. And just as it is wrong today, it was wrong then. We take responsibility for that and I unreservedly apologize on behalf of the district for that event."

Social media posts about the former "slave day" sparked anger online.

Robertson said she thinks the teachers involved didn't know better at the time.

"Both of them were both genuine, whole-hearted people. Racist? I would never put that label on either of them," she said.

But Mohammed says the teachers should publicly apologize or lose their jobs.