Caitlin Prater-Haacke had been sent a message on Facebook telling her to kill herself.
"I read the post and honestly I felt like throwing up," said the teen's mother Nicole Haacke. "The words that were used, they're not words I use in my own house."
Instead of replying to the message, Prater-Haacke took out a marker and some small pads of paper.
She decided to fight back by posting positive messages on every locker in her school.
"Little simple messages like, 'You're beautiful' [and] 'You shine bright like a diamond,'" she said.
School changes tune
But officials at George McDougall High School didn't like the idea and told her it was littering, which didn't sit well with the community.
City council then declared Oct. 9 as Positive Post-it Day.
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"What's come out of it is 100 times better," said Prater-Haacke, adding she can't believe the support she has received.
The school is now filled with the sticky notes, and this time the school says the colourful messages can stay.
But it wasn't just among students, as other Airdrie residents also embraced the movement.
"I think it put a smile on everyone's face this morning and I think it gave them that little bit of extra oomph for the morning to get them going," said resident David Jones.
The campaign has taken off online. A Facebook page was started and the Twitter hashtags #caitlinhaacke and #PositivePostit have started trending.